Inherited cardiovascular disorders

Subaortic stenosis

roblib — Mon, 29 Mar 2010 15:58:47 +0000

What is ... ?:

Subaortic stenosis is a common, potentially devastating birth defect of the heart in dogs. It consists of excessive tissue that partially blocks the path for outflow of blood from the heart to the circulation, creating a partial obstruction. The result is an increase in strain on the main pumping chamber of the heart, the left ventricle, as the heart works harder to maintain a normal circulation. In severe cases, subaortic stenosis can be fatal, but in mild cases it produces no problems (no symptoms, no need for treatment) in the affected dog. Subaortic stenosis is almost always inherited, so all affected dogs, whether mild or severe, should be removed from the breeding pool.

How is ... inherited?:

In virtually all cases in dogs, subaortic stenosis is inherited from the sire, the dam, or both. The degree of severity is highly variable, and a mildly affected individual may produce offspring with severe subaortic stenosis, or no subaortic stenosis at all (silent carriers). In Newfoundlands, subaortic stenosis has an autosomal dominant mode of inheritance, with variable expression. This means that if one parent has it, most of the offsrping will have it, but to a degree of severity that reaches across the spectrum, from undetectable to life-threatening.
The two major challenges for breeders and veterinarians are: 1) to identify affected dogs and exclude them from the breeding pool, which can be difficult with very mild subaortic stenosis (overlap with normal, athletic hearts); and 2) to avoid overreacting and culling too many individuals (the "if there's a heart murmur, don't breed" mentality), which leads to excessive elimination of good breeding stock, a smaller gene pool, and inevitably, the emergence of other inbreeding-related problems later on. Therefore, an accurate confirmation of subaortic stenosis, and judicious breeding decisions, are essential.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

The degree of concern and of impact on an individual dog depends on how much of an obstruction the subaortic stenosis is causing; i.e., on the degree of severity of the obstruction. Dogs with mild subaortic stenosis will generally experience no adverse health effects and have a normal life expectancy. With moderate to severe subaortic stenosis, symptoms and effects on health are variable. In general, some degree of exercise restriction in these cases is wise: at higher heart rates, the extra workload imposed on the heart is poorly tolerated and life-threatening complications can occur. Therefore, dogs with moderate or severe subaortic stenosis should avoid "adrenaline rushes" (sympathetic surges) such as sprinting or jumping. Rather, controlled, steady walks (on-leash) are much safer for the heart and still allow a dog to be outdoors and exercising. Reduced exercise tolerance -when a dog just seems to run out of steam- or fainting, due to inadequate blood supply to the brain, are signs of excessive physical activity that is outstripping the heart's capacity; physical activity should never reach a point where it causes such symptoms because a dog may collapse and not survive this degree of strain on the heart.

In response to the obstruction to blood flow caused by subaortic stenosis, the heart muscle tissue becomes thicker over time (left ventricular hypertrophy), crowding out the space in the heart available for blood. Over time, dogs with severe subaortic stenosis can have serious limitations in heart function, and symptoms such as difficulty in breathing, fits of uncomfortable coughing, and/or poor growth (in puppies) are possible. Any of these symptoms warrants a visit to the veterinarian, as the problem may be life-threatening and medications may need to start to be given immediately. At its worst, subaortic stenosis can cause changes in the heart muscle tissue that trigger an erratic, unstable heartbeat (cardiac arrythmias), which can be fatal.

How is ... diagnosed?:

Subaortic stenosis is almost always first suspected based on a heart murmur detected by the veterinarian. This presents a dilemma, because many other reasons exist for heart murmurs, many of which are harmless. Subaortic stenosis is a common cause of heart murmurs, but many dogs with normal hearts and no subaortic stenosis have heart murmurs as well. The dilemma cannot be resolved just by listening to the heart: even the most experienced veterinary cardiologists cannot confirm or eliminate subaortic stenosis just from listening to the heart. Therefore, tests are necessary to identify subaortic stenosis. The diagnostic test of choice is an echocardiogram, also called cardiac ultrasound or sonogram of the heart. The severity of subaortic stenosis depends on the degree of narrowing it is causing; this is assessed by measuring the pressure gradient across the aortic valve (between the left ventricle and the aorta) using Doppler ultrasound. Such testing is best performed by a veterinary cardiologist, and general practitioner veterianrians can refer their patients to one of these specialists for a confirmatory opinion (directories are available at www.acvim.org and www.ecvim-ca.org for veterinary cardiologists in North America and Europe, respectively).

It is important to realize that a grey zone exists between being clearly normal and being clearly affected with subaortic stenosis. Occasionally, dogs can have features that are neither convincing for subaortic stenosis nor convincingly normal, even on cardiac ultrasound. In these "indeterminate status" dogs, where subaortic stenosis is neither confirmed nor definitively eliminated, a moratorium may be imposed on breeding, but the dog should not be spayed or castrated. Rather, a follow-up examination several months or a year later may reveal a result that is clear.

Finally, dogs that are affected to a degree that they show overt symptoms, such as laboured breathing or collapse/fainting, generally require an electrocardiogram (EKG/ECG), a blood test (complete blood count, serum biochemistry profile), and thoracic radiographs (chest X-rays) to stage the problem and make decisions regarding starting medications.

How is ... treated?:

In dogs with mild subaortic stenosis, there is no treatment required. The dog should not be used for breeding, and littermates should be carefully screened.

With moderate to severe stenosis, the dog's exercise should be restricted: vigorous running and jumping are examples of activities that put a great deal of strain on the heart and could be permanently damaging; therefore, such activities shold be stopped or minimized, seeking the best balance between safety for the heart and enjoyment of controlled, mild to moderate physical activity. Beta-blocking medications such as atenolol, metoprolol, or carvedilol are often warranted with moderate or severe subaortic stenosis. These medications are given every day and they have a protective effect: they minimize the strain on hypertrophied cardiac tissue.
In dogs showing overt symptoms due to fluid retention in the lungs, treatment may include diuretics (such as furosemide) and ACE inhibitors (such as enalapril, benazepril, ramipril, imidapril, or lisinopril). These medications are given by mouth every day at home and help to alleviate the symptoms.
Various surgeries have been attempted to alleviate the obstruction of subaortic stenosis. These are never required in cases of mild subaortic stenosis, but may be useful for moderate or severe cases. The most promising at present is cutting-balloon valvuloplasty, a minimally-invasive (catheter-based) procedure that partially opens the narrowing caused by subaortic stenosis. Surgeries of this type are available in limited numbers of secialized veterinary facilities, and general practitioner veterinarians can arrange a referral to a specialty institution for this purpose.

For the veterinarian:

MURMUR: systolic, left hemithorax commonly radiating to the right (due to aortic root malposition) and possibly into thoracic inlet and up the neck; PMI left heart base (3rd to 4th intercostal space), may be equally loud or louder at right heart base.
ECG: often normal in mild or moderate cases; over time, ECG may show evidence of left ventricular enlargement (e.g., tall R waves in lead II), possibly evidence of myocardial hypoxia via ST segment depression or elevation, possibly ventricular arrhythmias. Overall, these changes are highly variable from one case to the next, and ECG is a poor screening test for subaortic stenosis.
RADIOGRAPHS: in severe cases, radiographs may show evidence of left ventricular enlargement, cranial aortic enlargement, left axis shift. Pulmonary vasculature is normal. Overall, these changes are highly variable, and radiographs are a poor screening test for subaortic stenosis.
ECHOCARDIOGRAPHY: diagnostic test of choice. Results include an increased left ventricular outflow tract velocity and left ventricular : aortic pressure gradient. Left ventricular hypertrophy, a subvalvular fibrous ring, and poststenotic dilation of the ascending aorta are possible in some cases.
OTHER: On physical exam in dogs with severe subaortic stenosis, the arterial pulse may be of reduced intensity and slow to rise ("pulsus parvus et tardus") and the systolic murmur may radiate such that it is audible on the dorsal surface of the skull.

Breeding advice:

Affected individuals should not be used for breeding, and littermates should be carefully screened.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Oyama MA, Sisson DD, Thomas WP, Bonagura JD. Congenital heart disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1250-1298.
Belanger M-C. Subaortic stenosis. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 1057-1059.

Atrial septal defect (ASD)

roblib — Tue, 30 Mar 2010 14:19:47 +0000

What is ... ?:

In dogs, as in people, the heart is made up of 4 chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle. As the name implies, an atrial septal defect is a defect or hole in the muscular wall -the atrial septum- that normally separates the right and left atria. It is often referred to in layperson's terms as a "hole in the heart," which is correct but potentially misleading: there is no hole causing blood loss out of the heart, but rather just an opening between two regions within the heart that should normally be separated from each other.

The result of an atrial septal defect is unnecessary recirculation of blood inside the heart. An atrial septal defect can therefore be considered a needless shortcut: part of the blood meant to go out to the circulation instead returns within the heart. This disturbance is inefficient, and the workload on the heart increases in order to maintain an adequate circulation. With large atrial septal defects, the result may be exhaustion of the heart and congestive heart failure, but with small atrial septal defects, dogs often do not know they have it and there is no long-term adverse consequence.

How is ... inherited?:

The mode of inheritance is not known for atrial septal defects, but many congenital cardiac defects are believed to have a polygenic mode of inheritance, with variable expression. This means that many individual genetic contributors must exist to result in an atrial septal defect.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

The main determinant of the impact of an atrial septal defect is its size. A small defect usually will be of no significance to a dog, and indeed most dogs with small atrial septal defects live normal lives.

With larger defects, however, there will be abnormal blood flow from the higher pressure left side of the heart across the defect to the right side. This causes more work for the heart , which can eventually lead to congestive heart failure. Signs may include respiratory difficulties, fainting, tiring with exercise, abnormal cardiac rhythms, and abdominal swelling due to fluid retention from the disrupted circulation.

How is ... diagnosed?:

Often, as with most heart defects, the first indication of a problem is when the veterinarian hears a heart murmur during a puppy's first physical examination for vaccinations (8-10 weeks of age). In the most serious cases, with very large atrial septal defects, there may be visible symptoms, such as exercise intolerance or respiratory difficulties, that prompt a visit to the veterinarian, where an atrial septal defect is discovered.

A heart murmur alone is never conclusive for atrial septal defects, because many other cardiac defects cause similar murmurs, and many pups may have healthy hearts and a murmur that goes away after a few weeks as part of normal growth. Therefore, if the features of a heart murmur make the veterinarian suspicious of the possibility of an atrial septal defect, then he or she will recommend tests, especially thoracic radiographs (chest X-rays) and an echocardiogram (also called cardiac ultrasound or sonogram of the heart). These noninvasive tests can identify clearly whether an atrial septal defect is present, and if it is, whether there is reason for concern (and whether treatment is necessary).

How is ... treated?:

In humans, surgical closure of an atrial septal defect is commonplace, and can be undertaken either with open-heart surgery or with minimally-invasive catheter-based interventions. In dogs, such operations are challenging and rarely undertaken. In the absence of symptoms, most dogs with atrial septal defects do not receive treatment. Thankfully, most dogs with atrial septal defects have small defects that are of no consequence. Dogs whose atrial septal defect is sufficiently large to cause symptoms receive oral medications at home to alleviate the symptoms rather than treating the underlying cause.

For the veterinarian:

MURMUR: classically, soft, mid-systolic ejection murmur; loudest in pulmonic area, left cranial thorax. The murmur is due to overcirculation -left-to-right shunting ASD- through a normal pulmonic valve, causing a murmur of relative pulmonic stenosis. Audible splitting of the second heart sound is possible but often very subtle.
ELECTROCARDIOGRAM: often normal; evidence of atrial enlargement (abnormally large P waves) is possible.
RADIOGRAPHS: may be normal with small defects; with larger defects, evidence of left and right atrial enlargement is common; evidence of right ventricular hypertrophy, and pulmonary overcirculation, also are variably present dependent on magnitude of shunting.
ECHOCARDIOGRAPHY: diagnostic test of choice for confirming presence and magnitude/size of atrial septal defect, and ruling in or ruling out concurrent defects.

Breeding advice:

Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Wey A. Atrial septal defect. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 113-115.
Oyama MA, Sisson DD, Thomas WP, Bonagura JD. Congenital heart disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1250-1298.

Dilated cardiomyopathy

roblib — Tue, 30 Mar 2010 14:27:20 +0000

What is ... ?:

Cardiomyopathy refers to disease of the heart muscle tissue (the myocardium). In veterinary medicine, there are 3 main types of cardiomyopathy:

Dilated cardiomyopathy. This is by far the most common type in the dog, and is the subject of all the sections, below. With dilated cardiomyopathy, there is dilation of the chambers of the ventricles of the heart, caused by an inherent weakness in the muscle structure of the heart. The heart itself becomes enlarged, bloated, and unable to contract adequately, severely hampering the circulation.
Hypertrophic cardiomyopathy. In this form of cardiomyopathy, there is a tremendous increase in the mass of the heart muscle tissue, with a resultant decrease in internal heart chamber size. While it is very common in the cat, hypertrophic cardiomyopathy is very rare in the dog.
Restrictive cardiomyopathy. In this form of cardiomyopathy, the heart appears normal but infiltration of stiff, inelastic tissue within the walls of the heart severely restricts the heart's ability to fill adequately. Restrictive cardiomyopathy occurs with some frequency in cats but has never been identified in dogs.

With any type of cardiomyopathy, the heart and circulation are forced to work harder to maintain blood perfusion to the organs of the body. If it is severe enough, cardiomyopathy may disrupt the circulation, causing fluid accumulation in the lungs and body cavities (congestive heart failure), or may give rise to erratic, unstable rhythms to the heartbeat (arrhythmias) that are potentially fatal.

How is ... inherited?:

Dilated cardiomyopathy can be transmitted genetically from parent to offspring, as evidenced by the high prevalence in certain specific giant breeds of dogs (see below). The exact mode of transmission is unknown, but a sex-linked mode may exist given the higher occurrence in males than females.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Dilated cardiomyopathy is a potentially severe, debilitating, but painless, disease of adult dogs (typically between 5 and 10 years of age). Overall, it almost always worsens over time, beginning with an asymptomatic period where dogs (and their families/breeders) have no way of suspecting that it exists: there are no symptoms or detectable abnormalities. This asymptomatic period, where the condition is referred to as "occult dilated cardiomyopathy" because it remains hidden, can last for years. Indeed, one of the reasons dilated cardiomyopathy spreads so widely within breeds is that it may only be detected long after a dog's breeding career is underway and the condition has been passed on to subsequent generations.
Dilated cardiomyopathy usually is first suspected when symptoms emerge, including respiratory difficulty (even severe breathlessness/unrelenting gasping for air), loss of appetite, sudden decrease in willingness or ability to exercise, weakness, episodes of collapse, and/or a bloated, pot-bellied abdomen. Prior to the appearance of such symptoms, no medication has been convincingly shown to help prolong quality of life or lifespan. Once these kinds of symptoms occur, however, medications (given at home, daily, as oral tablets or capsules) are indispensable for survival. When Doberman dogs develop these symptoms, the outlook may be very serious: even with medication, approximately one-third may not survive for more than a few days; about one-third improve and feel well for several weeks before worsening despite medication and either beign euthanized or dying; and the remaining one-third do well for months to a year or more.

In addition to the symptoms outlined above, a distinctive feature of this disorder in Doberman pinschers and boxers is that abnormal heart rhythms may originate in the heart and can be quite serious. These arrhythmias (atrial fibrillation, ventricular tachycardia) can worsen over time and may cause the heartbeat to be unstable. This is perhaps the most suddenly devastating aspect of dilated cardiomyopathy: that it can cause immediate, collapse (like a person who has a heart attack) and that a dog may not survive.
When a dog is suspected of having dilated cardiomyopathy, the most important first step is confirmation, because this heart disorder can be so serious. An echocardiogram (also called ultrasound of the heart or cardiac sonogram) should be performed by a board-certified veterinary cardiologist. This painless, noninvasive procedure lets the cardiologist examine the heart in real time, and assess its structure and function. The abnormality of dilated cardiomyopathy may be subtle, and there is much overlap between normal and early dilated cardiomyopathy. For this reason, a skilled specialist should be consulted.
If dilated cardiomyopathy is confirmed, treatment may or may not be necessary depending on the degree/stage of the problem. The outlook depends on findings obtained in diagnostic tests (see below).

How is ... diagnosed?:

As stated above, the test of choice for confirming dilated cardiomyopathy is an echocardiogram: an ultrasound of the heart. The echocardiogram cannot rely only on left ventricular fractional shortening for providing the diagnosis; it must include absolute left ventricular dimensions and, if there is any uncertainty (given the large area of overlap between normal athletic hearts and early dilated cardiomyopathy), it needs to include left ventricular volume calculations using Simpson's method of disks. This is usually best accomplished by a veterinary cardiologist, and general practitioner veterinarians can refer their patients to these specialists (directories are available at www.acvim.org and www.ecvim-ca.org for North America and Europe, respectively).
Thoracic radiographs (X-rays of the chest) are appropriate in all suspected cases of dilated cardiomyopathy. In affected dogs, an enlarged heart silhouette is a common abnormal finding, and there may be evidence of fluid retention within the lung tissue (pulmonary edema) or surrounding and collapsing the lungs (pleural effusion).
An electrocardiogram (ECG, EKG) may be performed if an irregular heartbeat, or arrhythmia, is detected by the veterinarian when listening with the stethoscope.

If dilated cardiomyopathy is suspected and results from all routine diagnostic tests are normal, a 24 hour ambulatory electrocardiogram (Holter monitor) is often recommended. The unobtrusive monitor is worn by the dog during normal daily activities, and it records irregular heart rhythms.
When dilated cardiomyopathy is confirmed in a dog, routine blood and urine tests (complete blood count, serum biochemistry profile, urinalysis) are run prior to beginning medications, in order to identify any other problems that could interfere with treatment, and to establish a baseline for future comparison when monitoring the effects of medications.

How is ... treated?:

Treatment for dilated cardiomyopathy consists of medications given one or more times a day. Initially, if severe symptoms are observed, the medications may need to be given in teh hospital for the first 1-3 days, where some of the medications can be given by injection. Ultimately, home treatment consists of giving the medications orally, avoiding strenuous exercise, avoiding salty foods or treats, and monitoring for any return of symptoms that woud prompt a recheck visit and adjustment of medications. Commonly-used medications include a diuretic such as furosemide (Lasix), spironolactone, or torsemide (Demadex); a type of medication that vasodilates, or decreases the resistance to outflow of blood from the heart, thereby easing the heart's workload (ACE inhibitors such as enalapril [Enacard], benazepril [Fortekor], ramipril [Vasotop], or imidapril [Prilium]); digitalis (digoxin, Lanoxin); and inodilators such as pimobendan (Vetmedin). It is common for dogs to need to be on all 4 of these classes of medications, which demonstrates that close attention and medication administration at home is essential, and that treatment may become costly, especially in the largest breeds (since the amount of medication given is based on body weight). Dogs that respond well to medications usually do so within days or 1-2 weeks of starting treatment, and show an often dramatic improvement in their energy level, appetite and overall demeanour.
Decisions about initiating (and later, adjusting) treatment are based on several factors: whether the dog is showing symptoms such as weakness or collapse, whether arrhythmias are seen on the electrocardiogram, and whether there is fluid retention in the tissues due to disruption of the circulation. There is no surgery to correct dilated cardiomyopathy in dogs.

For the veterinarian:

RADIOGRAPHS (CHEST X-RAYS): may show generalized cardiomegaly with evidence of left atrial and ventricular enlargement predominating. In Dobermans, only left atrial enlargement may be evident.
ELECTROCARDIOGRAM: atrial fibrillation is seen in 75 to 80 per cent of giant-breed dogs with dilated cardiomyopathy. Premature ventricular complexes and/or ventricular tachycardia also are very common. There may be subtle changes such as tall R waves or wide QRS complexes (both consistent with left ventricular enlargement), or wide P waves (suggesting left atrial enlargement).
ECHOCARDIOGRAM: diagnostic test of choice. Left ventricular dilation is the earliest change (increase in left ventricular volume as measured by Simpson's method of discs; increase in absolute left ventricular diastolic diameter and E-point-to-septal separation as measured on M-mode). Reduced left ventricular contractility is observed last (=least reliable) and there is a great deal of overlap between LV fractional shortening in normal athletic dogs and early dilated cardiomyopathy. Left atrial enlargement and right-sided chamber enlargement also are common.
PHYSICAL EXAM: occasional to frequent premature beats, pulse deficits, paroxysmal tachyarrhythmias or a totally irregular ventricular rhythm, variability in femoral pulse strength.

Breeding advice:

Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening.

How can cardiomyopathy be controlled?
There are promising ways to approach the control of this disease. Although signs of heart failure are often not evident until middle or older age, abnormalities on the electrocardiogram are often apparent earlier. In affected breeds with a family history of cardiomyopathy and in ALL Doberman pinschers, breeding animals should be evaluated yearly for evidence of cardiac arryhthmias, using echocardiography with left ventricular volume measurement whenever possible, or an ambulatory (Holter) monitor otherwise. Asymptomatic dogs in which dilated cardiomyopathy has been identified through this type of screening (i.e., "occult dilated cardiomyopathy") should not be used for breeding.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Prosek R. Dilated cardiomyopathy. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 309-312.
Meurs KM. Myocardial disease: canine. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1320-1328.

Mitral valve dysplasia

roblib — Tue, 30 Mar 2010 14:43:57 +0000

What is ... ?:

In dogs as in people, the heart contains 4 chambers: 2 atria and 2 ventricles. The atrioventricular (AV) valves ensure that the blood flows from the atria to the ventricles when the heart beats. A defect in the mitral valve (the left atrioventricular valve) causes backflow of blood into the left atrium, also called mitral regurgitation or mitral valve insufficiency. This type of "leak" means the workload on the heart is increased to keep up with the demands of the circulation in the body. While mitral valve insufficiency is the most common adult-onset heart problem in older dogs, it may also occur from birth if the heart valve is malformed during embryonic growth. The term "mitral valve dysplasia" refers to this exact situation, where from the moment a pup is born, its mitral valve does not seal properly, and therefore imposes an increased workload on the heart.

How is ... inherited?:

Mitral valve dysplasia does occur more commonly in certain breeds, implicating a genetic basis. The exact pattern of inheritance has not been defined.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

The importance and impact of mitral valve dysplasia depend mainly on the degree of malformation of the heart valve. A mild degree of mitral valve dysplasia usually means no symptoms and a normal life, whereas severe mitral valve dysplasia can produce life-threatening symptoms even in the first year of life. Therefore, if mitral valve dysplasia is suspected, it is important to neither overreact nor underreact because dogs may do better or worse than expected: many dogs with mitral valve dysplasia do not show any outwardly visible symptoms and a good cardiac evaluation is necessary to determine whether there is cause for concern.

How is ... diagnosed?:

In the vast majority of cases, mitral valve dysplasia first emerges as a consideration based on the detection of a heart murmur with the stethoscope during a visit to the veterinarian. Most dogs show no external symptoms initially. Since may different situations can cause heart murmurs, it is important to investigate heart murmurs in order to be able to confirm or eliminate mitral valve dysplasia as the underlying cause. The best tests for assessing the possibility of mitral valve dysplasia are thoracic radiographs (chest X-rays) and an echocardiogram (also called ultrasound of the heart or cardiac sonogram). These tests are noninvasive and can be done on an outpatient basis. It is often necessary to have a referral to a veterinary cardiologist to have the tests done in the most reliable fashion (directories available at www.acvim.org and www.ecvim-ca.org for North America and Europe, respectively).

How is ... treated?:

Mitral valve dysplasia is treated with medications, given daily at home, if a point is reached where overt symptoms such as laboured breathing start to occur and radiographs (X-rays) confirm that this is due to the heart's dysfunction. These symptoms can happen over time, and the symptoms occur only in moderate or severe cases, when the circulation can become affected to such a degree that pulmonary edema (fluid congestion in the lungs) occurs. Therefore, medications like diuretics help to eliminate retained lung fluid if it is present. Surgical replacement of the heart valve with an artificial, prosthetic valve, as is done in humans, is not feasible currrently in dogs.

For the veterinarian:

MURMUR: soft to loud, harsh, regurgitant, holosystolic - loudest at left apex (5th to 6th intercostal space) over the mitral valve area.
ELECTROCARDIOGRAM: commonly shows evidence of left atrial enlargement (wide P wave) with or without evidence of left ventricular enlargement (depends on severity). Atrial arrhythmias, especially atrial fibrillation, are common.
RADIOGRAPHS: evidence of moderate to marked left atrial enlargement with or without left ventricular enlargement. Pulmonary veins are often enlarged.
ECHOCARDIOGRAPHY: confirmatory test of choice. Typically shows abnormal location, shape, motion, or attachment of the valve apparatus in moderate or severe cases. Doppler assessment, especially colour-flow Doppler, will show an abnormal flow (regurgitant jet or valvular stenosis or both) in all clinically-significant cases.

Breeding advice:

Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Oyama MA, Sisson DD, Thomas WP, Bonagura JD. Congenital heart disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1250-1298.
Orvalho J. Mitral valve dysplasia. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 727-728.

Patent ductus arteriosus (PDA)

roblib — Tue, 30 Mar 2010 15:30:39 +0000

What is ... ?:

At birth, mammals must adapt from living in a fluid environment (the amniotic fluid in the mother's uterus) where they acquire oxygen through the mother's blood, to breathing air and acquiring oxygen through their own lungs. The ductus arteriosus is very important in the adaptation process. The ductus arteriosus is a normal, small communicating blood vessel beside the heart, connecting the pulmonary artery (which carries blood to the lungs) and the aorta (which carries blood to the rest of the body). Before birth, most of the blood from the fetal heart bypasses the fetal lungs via the ductus arteriosus. At birth, the blood supply from the mother is terminated when the umbilical cord is cut, the dog (or other mammal) begins breathing on its own, and blood flow through the ductus arteriosus is no longer necessary. Within a few days, the ductus shrinks and closes off completely.

Where the ductus arteriosus does not close within 24-48 hours after birth, the dog is left with a patent ductus arteriosus (PDA). PDA causes unnecessary recirculation of blood through the heart, greatly increasing the workload of the heart and potentially causing terminal heart failure in time if the PDA is not closed via surgery. The extent to which a PDA affects any given dog depends on the degree of patency, or size, of the ductus.

How is ... inherited?:

There is a sex-linked genetic predisposition for PDA: females are three times more likely to be affected than males, and PDA occurs disproportionately more often in specific breeds (see below), further indicating a genetic basis for the disorder. The exact lesion is hypoplasia of the smooth muscle of the wall of the ductus arteriosus; therefore, medications that cause ductal contraction (as used in children) are ineffective for PDA in dogs because the muscle tissue is missing from the wall of the ductus arteriosus.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

With very few exceptions, PDA causes such a significant increase in the workload of the heart that without surgery, it causes congestive heart failure before a normal lifespan -- and often in the first year or two of life. Therefore, a suspicion of PDA requires confirmation (see below) and treatment via surgery. Dogs never "outgrow" a PDA, and most dogs are fully asymptomatic when they have it: PDA causes no symptoms until very late in its course, when permanent damage to the heart has occurred.
The speed and degree of damage caused by PDA varies, depending on the magnitude of the defect. This cannot be known from physical examination alone; tests are needed to identify the size of the PDA (larger is worse) and the corresponding impact on the heart and the rest of the body's circulation.
Most commonly with PDA, there is a shunt from the left to the right side of the heart, with blood from the higher pressure aorta continuously shunted to the main pulmonary artery. This means an increased volume of blood to the lungs which results in fluid accumulation in the lung tissue (pulmonary edema) and volume overload of the left heart. Left unchecked, these consequences may lead to life-threatening overt symptoms such as breathlessness/very laboured breathing due to poor oxygenation, severely reduced tolerance of exercise, and even fainting or collapsing.

Much less commonly (about 2% of PDA cases), there is a right-to-left shunt. This may be the case from birth, or it may develop because the PDA is so large that the pressure in the lungs, and resultant resistance to this pressure, markedly increase. In effect, the circulation is the same as when the dog was a fetus - that is, some of the blood leaving the right side of the heart bypasses the lungs entirely. This results in circulation of poorly oxygenated blood. Dogs with right-to-left shunting PDA classically have weakness or collapse of the hindlegs associated with exercise: they slow down and sit mid-walk and are reluctant to start again, but eventually do, only to slow down and sit again as the poorly-oxygenated hindlegs become weak and cramped.

How is ... diagnosed?:

Usually a PDA is first suspected when the veterinarian hears a telltale type of heart murmur -the "machinery," or "washing-machine" continuous heart murmur- with the stethoscope when examining a dog during puppyhood as part of a routine appointment for vaccinations. Much less commonly the heart murmur may go unnoticed until later, when overt symptoms emerge, as described above. Either way, any suspicion of PDA warrants confirmation, which requires thoracic radiographs (X-rays of the chest) and an echocardiogram (also called cardiac ultrasound, or sonogram of the heart). These tests identify the PDA itself, its secondary effects on the heart and lungs, and any concurrent, unrelated heart defects that sometimes can be masked by PDA and help to determine whether a dog is a good surgical candidate for PDA repair.

How is ... treated?:

Surgery is recommended for all dogs with PDA, except the few (2%) that have right-to-left shunting and therefore, no heart murmur. Historically, surgery consisted of an operation under general anesthesia involving thoracotomy (open-chest, closed-heart procedure) to ligate the ductus and close it permanently with stitches. Nowadays, a minimally invasive procedure has replaced this approach in a majority of cases. The catheter-based approach, called deployment of an Amplatzer canine ductal occluder, involves passage of a self-expanding double-umbrella-shaped plug that closes the ductus from within. Like angioplasty in a person, this procedure does not require opening the chest, but rather is performed by passing a catheter through the femoral vein (in the groin) or jugular vein (in the neck).
When surgery is performed early and successfully, the long-term outlook for a normal life is generally excellent. That is, surgery performed when there is only a murmur and the puppy feels well has the greatest chance of success: changes in the heart caused by the PDA can return to normal and there may be no permanent damage at all.
Where there are overt symptoms, the treatment of choice remains surgery because the underlying problem must be corrected. The degree of secondary damage to the heart is highly variable and often can only be known in hindsight: the surgery must be performed and a recheck 6-8 weeks post-operatively reveals the degree of improvement and expected long-term outlook (i.e., whether medications will need to be given, whether a normal lifespan may be expeted, etc.).

The problems associated with the far less common right-to-left shunt are managed without surgery. Treatment includes mild exercise restriction (avoiding vigorous or prolonged activity) and avoidance of stress. Medications, and/or periodic bloodletting (phlebotomy) can help improve circulation in these cases.

For the veterinarian:

MURMUR: classically, a continuous "machinery" -type murmur that generally is loudest very cranially on the left side of the chest: in the axilla, over the 2nd or 3rd intercostal space. Failure to listen sufficiently cranially (deep in the left axilla) or sufficiently completely (ending the auscultation prematurely if the pup is whining, sniffing, or moving) is the most common reason for failure to diagnose patent ductus arteriosus early. There is no murmur in cases of right-to-left shunting PDA.
ELECTROCARDIOGRAM: signs of left atrial enlargement, and dramatic left ventricular dilation and hypertrophy (markedly tall R waves) are common but may overlap with normal in many cases. Signs of right ventricular hypertrophy (right axis deviation) are common with right-to-left shunting PDA.
RADIOGRAPHS: varying degrees of pulmonary overcirculation, left atrial and ventricular enlargement (may be extreme), and possibly focal dilation of the descending aorta and main pulmonary artery are typical. Evidence of right ventricular hypertrophy may occur with right-to-left shunting PDAs.
ECHOCARDIOGRAPHY: left atrial and ventricular dilation with preserved or increased contractility; with careful evaluation, the ductus itself can usually be demonstrated in the left or right cranial short-axis views. Doppler evaluation invariably demonstrates turbulent blood flow in the proximal pulmonary artery in left-to-right shunting PDAs.
OTHER: signs of pulmonary edema and left-sided heart failure may be present when PDA has been left undiagnosed/untreated, leading to decompensation. With the rare, right-to-left shunting PDAs, unoxygenated blood directly from the pulmonary artery mixes with oxygenated blood in the descending aorta, causing hindlimb weakness and differential cyanosis (cyanosis afffects the caudal half of the body but not the cranial half); desaturated arterial blood perfusing the kidneys causes renal hypoxia, erythropoietin excess, polycythemia, and hyperviscosity, and the packed cell volume often exceeds 65 per cent.

Breeding advice:

Dogs in whom PDA has been diagnosed, with or without surgical correction, should not be used for breeding. Their parents should not be bred either, and siblings should only be used after careful screening. If any affected offspring are born, breeding of the parents should be discontinued.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Oyama MA, Sisson DD, Thomas WP, Bonagura, JD. Congenital heart disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1250-1298.
Buchanan JW. Patent ductus arteriosus. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats (St. Louis, MO: Mosby Elsevier, 2011) pp. 843-845.

Portosystemic shunt

roblib — Tue, 30 Mar 2010 15:51:27 +0000

What is ... ?:

Portosystemic shunt (PSS) is a birth defect of the circulation in the liver. In animals with a PSS, there is abnormal blood flow through the liver. Blood should flow from the digestive tract (stomach, intestines) to the liver via the portal system into the blood vessels of the liver, and then to the caudal vena cava which is the large blood vessel carrying blood back to the heart. This way, blood normally percolates through the liver where it is detoxified. In a portosystemic shunt, as the name implies, an accidental shortcut is created: portal blood bypasses the liver and goes directly to the systemic venous circulation (caudal vena cava), without having filtered through the liver tissue. This has very important repercussions because one of the main functions of the liver is to eliminate toxins from the bloodstream. In PSS, blood bypasses the liver and therefore these toxins are not cleared, remaining in the circulation throughout the body. The result is symptoms of PSS, many of which are neurological because the toxins alter the brain's capacity to maintain a dog alert and responsive. The complex of neurological and behavioural signs caused by liver dysfunction is called hepatic encephalopathy.

Portosystemic shunts may occur as intra-hepatic or extra-hepatic depending on the location of the blood vessel in relation to the liver. That is, intrahepatic PSSs are malformations within the liver, whereas extrahepatic PSSs are malformations just upstream from the liver. The location of a PSS is important because it determines the best way to correct it via surgery.

Most animals with congenital portosystemic shunts show symptoms before 6 months of age. When symptoms are subtle, however, the condition may not be diagnosed until much later.

How is ... inherited?:

The exact mode of inheritance is not known, but a genetic basis is clearly indicated by higher-than-average occurrence in certain breeds (see below).

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

The symptoms of PSS tend to emerge during puppyhood. These symptoms generally are associated with the central nervous system, the gastrointestinal tract, or the urinary tract. Most consistently, there are signs of hepatic encephalopathy - neurological and behavioural evidence of diffuse brain dysfunction due to liver dysfunction. Examples include loss of appetite, mental dullness, lethargy and sluggishness, weakness, poor balance, disorientation, blindness, seizures, and even coma. The symptoms may wax and wane, and may worsen after eating a protein-rich meal.

With PSS, a pup's growth may seem to be stunted or slower than the growth of littermates and age-mates. Indeed, "runts" of litters often turn out to be puppies that have birth defects, and PSS is a very common one of these.
Failure of the liver to clear ammonia means that there will be increased excretion in the urine. This commonly leads to urolithiasis - kidney, bladder, or urethral calculi (stones) due to the build-up of mineral salts. Any young dog with urolithiasis (stones in the bladder, urethra, or kidneys) should be checked for PSS.

The first sign of PSS in a dog may be a prolonged recovery from anesthesia, or excessive sedation after treatment with some medications. This occurs because with PSS, anesthetics and medications are not filtered out of the blood and broken down as they would normally be by the liver, but instead are recirculated in the body.
The impact of PSS may not be apparent at first. Symptoms tend to worsen with age, and the decision to treat (via surgery) should be made as early as possible. Dogs do not outgrow PSS; surgery should be performed when a puppy is still growing, to minimize the risk of permanent damage. Dogs who are not candidates for surgery, either because they have a form of PSS that is inoperable or because surgery is not an option due to cost or availability, may still benefit from orally-administered medications at home.
It is very important to realize that the final result of surgery for PSS can only be known weeks after the surgery has been done. The effects of PSS take time to subside, and the body's ability to adapt back to normal after the surgical correction is different in every dog: many become totally normal and have normal lives, whereas some have irreversible damage associated with the PSS, and surgery only partially corrects these changes.

How is ... diagnosed?:

Generally, the diagnosis of PSS is suspected based on a combination of the medical history (such as delayed anesthetic recovery or previous surgery for urolith/urinary tract stone removal), symptoms (such as those described above), and results of laboratory tests. The screening test of choice is a routine laboratory panel (complete blood count, serum biochemistry profile, and urinalysis) with serum bile acids, which is a specific blood test that requires a 12-hour fasting period beforehand and takes 2-3 hours.
The confirmatory test of choice is a high-detail abdominal ultrasound examination by a specialist (radiologist or internist); nuclear scintigraphy (a type of scan) also is highly definitive but is less widely available. Either test is noninvasive and is generally done without sedation.

The screening blood test, serum bile acids, is highly accurate, with a nearly 100% ability to detect PSS in dogs that have it. A positive test still requires ultrasound/scan confirmation, because other disorders such as hepatic microvascular dysplasia, which is an incurable, microscopic version of PSS where thousands of small shunts ("shortcuts") cause blood to bypass the liver at the tissue level, may be present instead. Hepatic microvascular dysplasia can only be confirmed with a liver biopsy, so it is routine for dogs that undergo surgery for PSS to also have a liver biopsy, for identifying whether hepatic microvascular dysplasia is also present. This alters the long-term outlook: dogs with PSS but without microvascular dysplasia have a better long-term outlook for living free of symptoms and without medications.

How is ... treated?:

The most definitive way to deal with PSS is surgery. The surgeon identifies the path of blood bypassing the liver and closes it, forcing the blood to follow the new, normal course through the liver. This type of surgery is an open-abdominal procedure, meaning general anesthesia is warranted and a period of recovery, typically lasting 1-4 days in the hospital and 2 weeks or so at home, is to be expected. The success rate of surgery is high (>90%) but not perfect; even in the most experienced hands, some dogs with PSS who also have microvascular dysplasia or other circulatory defect through the liver may not tolerate the operation and may need only partial closure of the shunt. Other dogs do not tolerate any correction of PSS and this is only apparent during the operation. To improve the chances of success, surgeons often repair PSS by inserting a device that closes the PSS gradually, over several weeks. Surgeons also will be careful to monitor a dog's status both before the surgery and during the post-operative period; the liver performs so many essential functions that careful monitoring and medical support, such as with plasma transfusions, antibiotics, or other treatments, are essential.
In some cases, PSS may involve a single shunt that is buried deep within the liver tissue: intra-hepatic PSS. These situations are difficult to correct in the manner described above, and a better option in such cases is minimally-invasive occlusion (closure) of the shunt through catheter-based techniques. Briefly, this approach does not involve surgical opening of the abdomen but rather involves a surgeon placing a catheter through a blood vessel in the groin and steering the catheter to the location of the shunt within the liver under fluoroscopic, real-time X-ray guidance. The surgeon can then deploy a device that occludes (blocks) blood flow at that level, redirecting it into the normal path. This is an extremely challenging procedure performed only at certain specialist referral hospitals; discussing this possibility with a general practitioner veterinarians is the first step, followed by referral if the features of the PSS are compatible with this procedure.
Finally, many dogs with very mild or no symptoms of PSS, especially if the condition is first identified after 5 years of age, may do well simply by receving oral medications and no surgery at all. To be clear, definitive (surgical) correction is the best treatment, but if the PSS is very minor and it escapes notice until age 5 years or thereafter, there may be more to be gained with a conservative approach and no surgery.

For the veterinarian:

COMPLETE BLOOD COUNT: often unremarkable. Subtle but important clues may include microcytosis, target cells, and/or a mild nonregenerative anemia.
BIOCHEMISTRY: mild abnormalities suggestive of hepatic dysfunction often are present, such as hypoproteinemia, hypoalbuminemia, hypoglycemia, low blood urea nitrogen, and normal to mild increases in serum liver enzymes. Elevated bilirubin levels are inconsistent with PSS and, if repeatable, suggest a different diagnosis. Postprandial serum bile acids (SBA) are consistently elevated (>99% sensitivity for PSS when >25 uM/l).
URINALYSIS: dogs with polyuria and polydipsia often are isosthenuric or hyposthenuric. Ammonium biurate crystals in the urine sediment are an important and common finding. Where urolithiasis occurs, there may also be hematuria, proteinuria, and/or pyuria.
PLAIN RADIOGRAPHY: microhepatica is common.
ADDITIONAL IMAGING TECHNIQUES: ultrasonography, rectal portal scintigraphy, and mesenteric portography (less commonly needed nowadays) can provide information about the presence, location, and type of shunt.

Breeding advice:

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Hart Jr, JR. Portosystemic shunt. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 905-907.
Berent AC, Weisse C. Hepatic vascular anomalies. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1649-1672.

Pulmonic stenosis

roblib — Tue, 30 Mar 2010 16:01:34 +0000

What is ... ?:

Pulmonic stenosis is a birth defect consisting of a narrowing in a region of the heart, the pulmonic valve (or adjacent area). A narrowing of the pulmonic valve increases the level of strain and workload on the chamber of the heart feeding into it, the right ventricle. Since normal blood flow requires heart valves to open fully for proper circulation, incomplete opening of the pulmonic valve (the hallmark of pulmonic stenosis) creates a "logjam" effect that disturbs blood flow and in the worst cases, may create life-threatening symptoms.
In mild and moderate pulmonic stenosis, where there is a small or medium degree of narrowing, respectively, the outlook for an individual dog is usually good to excellent: few dogs experience problems due to their pulmonic stenosis if it is mild or moderate in degree. Dogs with severe pulmonic sytenosis, however, may develop symptoms that become life-threatening in the future.
Screening for pulmonic stenosis is done at an early age: 8 weeks onward. The degree of severity of pulmonic stenosis may worsen as a puppy reaches adulthood. Therefore, mild or moderate pulmonic stenosis in a puppy should be followed until the dog is 12 to 18 months of age in order to know the final degree of seriousness of the condition.

How is ... inherited?:

Pulmonic stenosis appears to be inherited as a polygenic threshold trait. This means that more than one genetic aberration contributes to pulmonic stenosis; a genetic test for identifying it does not exist at this time.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Pulmonic stenosis is usually suspected based on a veterinarian's detecting a heart murmur when listening to a dog's heart with a stethoscope. Murmurs may be caused by many, many disorders, including pulmonic stenosis, so it is important to know that just having a heart murmur (of any grade) is not definitive for pulmonic stenosis.
If a heart murmur is detected and the veterinarian feels it could be due to pulmonic stenosis, he/she will recommend tests to confirm pulmonic stenosis or eliminate it from consideration. These tests are noninvasive and very accurate (see below), and they mainly help to answer two questions: "Is it pulmonic stenosis?" and if it is, "Is it severe enough that something needs to be done?".

How is ... diagnosed?:

The first indication of pulmonic stenosis is generally a heart murmur detected in a young dog (typically during puppy vaccine visits between the ages of 2 and 4 months). Much less commonly, dogs with severe pulmonic stenosis may develop symptoms such as abdominal enlargement -a bloated appearance to the belly, caused by fluid retention- or laboured breathing or collapse/fainting. Either way, a veterinarian's suspicion of pulmonic stenosis justifies doing thoracic radiographs (chest X-rays) and an echocardiogram (also called cardiac ultrasound, or sonogram of the heart). These tests help to pinpoint whether pulmonic stenosis is present and if it is, whether it is mild, moderate, or severe. Specifically, the echocardiogram can detect whether secondary changes such as thickening of the right ventricle or other distortion of the heart's structure has occurred, and the degree of strain under which the heart is forced to operate. The extra workload that pulmonic stenosis imposes on the heart is identified through Doppler ultrasound calculation of a pressure gradient between the right ventricle and pulmonary arteries. Based on this ultrasound-derived calculation, the degree of pulmonic stenosis is determined, and in turn it is then possible to know whether treatment is essential, or not required at all.

How is ... treated?:

Since pulmonic stenosis is a narrowing of a region in the heart, the degree of concern depends directly on the degree of narrowing. Mild or moderate stenosis generally does not require any intervention at all. In some cases, additional findings on X-rays or cardiac ultrasound may justify starting daily medication, but with mild or moderate pulmonic stenosis, this is uncommon.
With severe pulmonic stenosis, there is a strong likelihood of life-threatening problems at some point if treatment is not undertaken. Conversely, a good/normal quality of life and lifespan are expected with surgical treatment in the vast majority of cases. Surgery for pulmonic stenosis consists of enlarging the narrowed pulmonic valve so that circulation is improved and the strain on the heart is reduced. This is usually accomplished through minimally-invasive surgery: under general anesthesia, a catheter (long tube) is threaded through a blood vessel in the neck or groin and a balloon on it is inflated when it is positioned at the area of the pulmonic stenosis. The inflation of the balloon stretches the narrowed space in a way that tends to remain permanent, even after the balloon is deflated and the catheter removed. The long-term result is that the resistance to blood flow is lessened and the heart resumes a more normal degree of work.
Some dogs are not candidates for this type of surgery: severe pulmonic stenosis may sometimes be inoperable. In these cases, treatment with beta-blocking drugs, which protect the heart against the damaging effects of adrenaline rushes, may be advocated by the veterinarian as a preventive measure.
Dogs with mild pulmonic stenosis and most dogs with moderate pulmonic stenosis enjoy normal lives without treatment. Some dogs with moderate pulmonic stenosis and virtually all dogs with severe pulmonic stenosis have a shortened lifespan if it is left untreated. It is important to note that pulmonic stenosis does not cause pain, and it is not "wrong" or "unfair" to have a dog live with pulmonic stenosis of any degree of severity. The treatments described above are aimed at improving lifespan and quality of life in the future.

For the veterinarian:

MURMUR: systolic ejection murmur, loudest in pulmonic area near left cranial sternal border/left axilla, often radiating to the right cranial sternal border.
ELECTROCARDIOGRAM: evidence of RV hypertrophy (right axis shift), right atrial enlargement (P pulmonale), and arrhythmia associated with hypertrophy are possible; however, these abnormalities occur sporadically and may not exist even in severely-affected dogs. Therefore, electrocardiography should not be considered a screening test for trying to rule in or rule out pulmonic stenosis with any degree of certainty.
RADIOGRAPHS: evidence of right ventricular hypertrophy and poststenotic dilation of pulmonary artery are possible in cases of severe pulmonic stenosis. Many impostors (particularly related to positioning and chest conformation) mimic these findings, and radiographs should be used less as a screening test and more as an adjunct, particularly for identifying pleural effusion if right-sided congestive heart failure is suspected.
ECHOCARDIOGRAPHY: diagnostic test of choice for pulmonic stenosis. Typical findings include concentric RV hypertrophy, deformity and narrowing in the pulmonic valve, and poststenotic dilation of the pulmonary artery; the Doppler-derived gradient across the stenotic valve identifies the severity of the lesion.
OTHER: On physical exam, jugular pulses may be evident in severe cases (beware the impostor of carotid pulsations radiating through a normal jugular vein).

In English bulldogs and boxers, pulmonic stenosis is commonly caused by a left coronary artery anomaly which has important implications for surgical correction: these cases cannot be safely operated under normal circumstances, and referral to a cardiologist is recommended both for confirmation and to discuss treatment and outlook.

Breeding advice:

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Sisson DD. Pulmonic stenosis. In Cote E, ed. Clinical Veterinary Advisor, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 941-943.

Sick sinus syndrome

roblib — Tue, 30 Mar 2010 16:04:49 +0000

What is ... ?:

Sick sinus syndrome (also called sinus node dysfunction or bradycardia-tachycardia syndrome) is a disturbance of the normal rhythm of the heart in adult/older dogs. Normally, a dog's heart will beat at a rate as low as 40 beats/minute during sleep and as high as 280 beats/minute during intense exercise. In sick sinus syndrome, the heart's natural ability to beat is compromised. Some dogs suddenly have a heart rate as slow as 10 beats/minute, even during physical exercise; this causes a drastic drop in circulation, and then they recover for hours or days before having another sudden drop in heart rate. Other dogs have the opposite: a heart rate that suddenly is very fast, causing a pounding heartbeat and also compromising the circulation. Overall, then, sick sinus syndrome is a disorder that causes an erratic change in the heartbeat, and that begins mildly and then develops over time into a potentially life-threatening problem. The hallmark symptom of sick sinus syndrome is sudden loss of consciousness (fainting), also called syncope.

How is ... inherited?:

Sick sinus syndrome occurs much more often in specific breeds: miniature Schnauzers (females more than males), cocker spaniels, West Highland white terriers, and dachshunds. However, it can occur in any breed of dog. The exact genetic mechanism/mode of transmission is not known.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Sick sinus syndrome is a serious, potentially life-threatening disorder. That said, it does not affect the strength of the heart muscle tissue, and it does not cause pain. In other words, if the rhythm of the heartbeat can be stabilized, the outlook for dogs with sick sinus syndrome is very good. In dogs, as in people, the heart rhythm is stabilized through surgical implantation of a pacemaker. The vast majority of dogs who have sick sinus syndrome and receive a pacemaker live normal lives; the vast majority of dogs who have sick sinus syndrome but do not receive a pacemaker develop increasingly frequent and severe episodes of collapse and loss of consciousness, eventually proving fatal.

How is ... diagnosed?:

The first indication of this disorder may be that a veterinarian finds that an affected dog has an unusually slow heart rate, which is not increased by exercise. These asymptomatic dogs tend to have earlier, milder forms of sick sinus syndrome and may not develop life-threatening problems as quickly.
In other cases, the overt symptom of collapse and loss of consciousness may be the first clue that leads to finding sick sinus syndrome. These symptomatic dogs tend to require treatment quickly to avoid fatal collapse in the subsequent days to months.

Either way, an electrocardiogram (ECG, EKG) is necessary for observing the rhythm of the heartbeat and confirming that sick sinus syndrome is or is not present. Occasionally, an in-office ECG at the veterinary hospital is normal, and yet the intermittent loss of consicousness is still highly suggestive of sick sinus syndrome. If this is the case, the veterinarian may recommend a portable ECG monitor (Holter monitor or event monitor) that a dog can wear, and which can record the ECG under natural circumstances.
Confirming (or eliminating) sick sinus syndrome through definitive ECG recording is important in order to follow the correct treatment and give an accurate assessment of future outlook.

How is ... treated?:

When there are no overt symptoms (and sick sinus syndrome is only identified at a check-up, for example), treatment generally is not necessary. Two exceptions are if general anesthesia is planned (because sick sinus syndrome decreases cardiac reserves that are essential for safe anesthesia) or if the veterinarian identifies very, very slow heart rates. Treatment should be considered in such cases, and in all cases where there are marked ECG changes and/or significant symptoms such as frequent fainting. Certain medications may temporarily improve the heart's rhythm, but virtually all dogs with sick sinus syndrome ultimately require surgical implantation of a permanent pacemaker. The prognosis (outlook for a good life) with a pacemaker is very good.

For the veterinarian:

ELECTROCARDIOGRAM (ECG): common findings include any combination of severe and persistant sinus bradycardia, asystole, supraventricular premature complexes or tachycardia, bradycardia-tachycardia syndrome (periods of severe sinus bradycardia alternating with ectopic supraventricular tachycardias). Often, syncopal patients 1) have syncopal episodes that may not fit the description of classic syncope (e.g., the signs may overlap somewhat with seizures) and 2) may have perfectly normal ECG findings in the hospital (and no syncope in the hospital). The finding of a normal in-hospital ECG is inconclusive in such cases. For these reasons, portable ECG monitoring, such as Holter monitors or owner-activated event monitors, is extremely helpful for ruling in or ruling out sick sinus syndrome. Portable ECG monitoring is much safer than proceeding with a neurologic workup (cerebrospinal fluid tap, brain imaging) in ambiguous cases because general anesthesia is required for these neurologic procedures, and it may be catastrophic for an undiagnosed sick sinus syndrome patient.
Classically, neither exercise nor intravenous atropine were said to elevate the heart rate significantly. We now know that some dogs with sick sinus syndrome do respond to exercise or atropine, although such a response is not reliably predictive of successful response to oral (anticholinergic) medications.

Breeding advice:

Even though the specific mode of inheritance is not known, the occurrence of sick sinus syndrome in a breeding dog should be a discouraging factor with regards to future breeding.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Cote E. Electrocardiography and cardiac arrhythmias. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1159-1187.
Bulmer BJ. Sick sinus syndrome. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 1022-1024.

Tetralogy of Fallot

roblib — Tue, 30 Mar 2010 16:17:10 +0000

What is ... ?:

Tetralogy of Fallot is a rare but potentially very serious combination of defects in the heart that arise when the puppy is still growing as a fetus in the dam (mother). As the "tetra-" component of the name implies, tetralogy of Fallot consists of 4 defects inside the heart. These are: pulmonic stenosis, ventricular septal defect, dextroaorta/overriding aorta, and right ventricular concentric hypertrophy secondary to the pulmonic stenosis. Evidence suggests that these defects are the result of varying degrees of abnormality in a single developmental process - the growth and fusion of the conotruncal septum, a key region in the heart of a growing fetus.

In pulmonic stenosis, there is partial obstruction of blood flow from the right side of the heart through the pulmonic valve. Because of the obstruction, the right side of the heart has to work harder to pump blood to the lungs. This causes an increase in the mass of the heart muscle, or right ventricular hypertrophy, one of the hallmarks of this disorder.
A ventricular septal defect is a defect or hole in the muscular wall of the heart (the septum) that separates the right and left ventricles. This communication between two parts of the heart that are supposed to be separate is inefficient, and it causes an increase in workload of the heart.

Dextroaorta, or overriding aorta, diverts unoxygenated blood away from the lungs, where it should go to be oxygenated, and out to the body's tissues. Consequently, a dog with tetralogy of Fallot has tissues that exist in a state of constant oxygen deprivation, which explains the exercise intolerance and poor stamina commonly seen with this heart condition.
The result of the defects that make up tetralogy of Fallot is that the heart is forced to work harder than normal during every heartbeat, and poorly oxygenated blood is delivered to the tissues of the body.

How is ... inherited?:

While it can occur in any breed of dog, the keeshond is most commonly affected. Based on studies with affected keeshonden, the mode of inheritance is believed to be autosomal recessive with variable expression. This means that the problem can be transmitted from either the dam or the sire (or both) to a puppy, and that the degree of severity is unpredictable: in the same litter, some puipies may be gravely affected, some not at all, and some in between, in varying proportions.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

As with other heart defects, the presence of symptoms and overall impact of tetralogy of Fallot depends on the severity of the defect. If a dog has tetralogy of Fallot with a very mild degree of pulmonic stenosis and a small ventricular septal defect, for example, then he or she may only have a heart murmur and a normal life with no associated problems.

More serious cases are common, where puppies with this combination of defects experience weakness, failure to thrive and grow, a reduced tolerance for exercise, and general cyanosis (blue-grey coloration of the mucous membranes of the mouth and eyes, instead of the normal pale pink). These signs are the result of the delivery of poorly oxygenated blood to the different parts of the body.
Mildly affected dogs may enjoy a normal life, but dogs with symptoms such as those described above often have a shortened lifespan. Tetralogy of Fallot does not cause suffering (there is no pain associated with it) but in its most severe forms it can confine a dog to a quiet, easygoing lifestyle.

How is ... diagnosed?:

Puppies with severe cases of this disorder may be weak and may grow poorly, and such symptoms are initial clues to a veterinarian that tetralogy of Fallot may be present. On closer physical examination, a veterinarian may identify cyanosis, and a heart murmur is apparent on listening to the heart with a stethoscope in all cases of tetralogy of Fallot. Definitive confirmation comes with thoracic radiographs (X-rays of the chest) and an echocardiogram (ultrasound of the heart; cardiac sonogram), both of which are noninvasive tests that can be performed without sedation in a majority of dogs.

How is ... treated?:

Complex open-heart surgery is required to correct the condition, and this is routinely performed successfully in children. In dogs, however, surgery has a high mortality rate and is not considered a viable treatment option at this time.

In the absence of definitive correction through surgery, tetralogy of Fallot is managed by giving daily medication at home to reduce the impact of sympathetic activity ("adrenaline rushes") on the heart, which can be especially strenuous on sick hearts like those with tetralogy of Fallot. These medications are called beta-blockers and include such prescription medications as atenolol, metoprolol, or carvedilol. Some dogs with tetralogy of Fallot develop a very high red blood cell count, which further hampers adequate tissue oxygenation. In these dogs, periodic phlebotomy (bloodletting) may restore a more normal viscosity or thickness to the blood, and thus improve circulation, or a medication to reduce red blood cell formation in the body (hydroxyurea) may be prescribed for this purpose. Regardless, dogs with tetralogy of Fallot that require medications need to have regular medical checkups, often every few months.

For the veterinarian:

MURMUR: depends on the relative degree of pulmonic stenosis and size of the ventricular septal defect. Classically, a systolic ejection murmur, loudest over pulmonic valve area, is heard, with or without a concurrent right-sided apical systolic murmur due to turbulent flow through the ventricular septal defect. The net effect may simply be of one loud murmur ausculted widely over both sides of the chest.
ELECTROCARDIOGRAM: may suggest right ventricular hypertrophy (right axis deviation).
RADIOGRAPHS: classcally, evidence of right ventricular enlargement, diminished pulmonary vasculature, malpositioned aorta; post-stenotic dilation of main pulmonary artery possible.
ECHOCARDIOGRAPHY: conclusive diagnostic test. Right ventricular concentric hypertrophy, pulmonic stenosis, ventricular septal defect, dextroaorta. Contrast echocardiography may show right-to-left shunting across the ventricular septal defect, and in some cases may reveal a right-to-left shunting patent foramen ovale.
OTHER: cyanosis at rest or after exercise, polycythemia, low arterial oxygen concentration and saturation are possible.

Breeding advice:

Affected pups and their parents (assumed to be carriers) should not be bred. Siblings that appear normal after careful physical examination may be used for breeding, with meticulous follow-up of offspring. The offspring should be examined with echocardiography at age 8-12 weeks and, if affected, the breeding of the parents should be discontinued.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Oyama MA, Sisson DD, Thomas WP, Bonagura JD. Congenital heart disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1250-1298.
Bonagura JD. Tetralogy of Fallot. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 1084-1086.

Tricuspid valve dysplasia

roblib — Tue, 30 Mar 2010 16:24:13 +0000

What is ... ?:

The atrioventricular (AV) valves in the heart ensure that the blood flows in the correct direction inside the heart, from the atria to the ventricles, when the heart beats. When the AV valve in the right side of the heart -the tricuspid valve- is malformed at birth (called dysplasia of the valve), blood flow through the heart is less efficient: with each heartbeat, a portion of the blood that is meant to travel in the normal direction instead spills backward to where it just came from. This process, called tricuspid valve insufficiency or tricuspid valve regurgitation, requires the heart to work harder to overcome this inefficiency.

How is ... inherited?:

Tricuspid valve dysplasia is the most common birth defect of the heart in Labrador retrievers (yellow, black, and chocolate). It is inherited as an autosomal dominant trait with variable penetrance; it affects male and female puppies equally, it can be transmitted to pups from the sire or the dam (or both), and the degree of severity is unpredictable: some pups inherit it as a severe, life-shortening disorder whereas others have a mild form that never causes symptoms (or they may be completely normal in every detectable way but carry the genetic defect that leads to tricuspid dysplasia in later generations). The genetic defect for tricuspid valve dysplasia is found on chromosome 9 in dogs.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

The main determinant of the impact of tricuspid dysplasia is the degree of valve malformation. Dogs with a mildly or even moderately malformed tricuspid valve routinely live normal lifespans. However, dogs with severe tricuspid valve malformations, even as pups, may develop symptoms of congestive heart failure, especially a bloated, pot-bellied appearance due to fluid pooling in the abdomen (ascites), difficulty breathing due to fluid retention in the chest cavity (pleural effusion), or both. Such severely affected dogs require medications to reduce the impact of the problem and maintain an acceptable quality of life.

How is ... diagnosed?:

The veterinarian may detect a heart murmur long before an affected dog is showing any outwardly visible signs associated with tricuspid valve dysplasia. If a veterinarian detects a heart murmur and the murmur persists for more than 2-3 weeks, further investigation is always warranted. Tests can pinpoint tricuspid valve dysplasia as the problem and determine its degree of severity. Such tests generally include thoracic radiographs (X-rays of the chest) and an echocardiogram, also called sonogram of the heart, or cardiac ultrasound. Both are noninvasive procedures that can be performed awake or under mild sedation in virtually all dogs. The underlying problem (malformation of the tricuspid valve) as well as its impact (degree of distortion of surrounding heart chambers, for example) can be identified if present. This information helps determine whether treatment is necessary and whether the outlook is good, fair, or poor.

How is ... treated?:

Mild and even moderate cases of tricuspid dysplasia usually do not require any treatment at all. Mild exercise restriction may be wise, to reduce the strain on the tricuspid valve (which is at its worst during bursts of intense physical activity). Surgical replacement of the tricuspid valve is not feasible in dogs as it is in people; therefore, pre-emptive/early-stage treatment is not appropriate in the dog. Rather, dogs with tricuspid valve dysplasia should be observed at home for signs of abdominal enlargement or difficulty breathing. If such symptoms occur, then a recheck with the veterinarian is warranted, both to confirm that the symptoms are due to the heart (there are many noncardiac disorders that can mimic these symptoms) and to begin medication immediately if confirmed.

For the veterinarian:

MURMUR: soft to loud holosystolic murmur over the tricuspid valve and right apex area (fourth intercostal space at costochondral junction). Failure to auscult carefully over the right side of the chest is a common reason for underdiagnosis of tricuspid dysplasia, and a meticulous auscultation in this region is warranted, especially in Labradors.
ELECTROCARDIOGRAM: right atrial and ventricular enlargement patterns are possible (tall P waves and right axis deviation, respectively). Atrial arrhythmias, especially atrial fibrillation, are common. Ventricular conduction disturbances may be seen, notably splintering of the QRS complex.
RADIOGRAPHS: evidence of right atrial and ventricular enlargement is almost always present in moderate cases and these changes may be dramatic in severe cases. Pulmonary undercirculation is possible in severe cases. Pleural effusion is possible with right-sided congestive heart failure.
ECHOCARDIOGRAPHY: abnormal location, shape, movement, or attachment of the valve apparatus are the hallmarks of this disorder. Doppler assessment will show abnormal flow in most cases - a regurgitant jet, evidence of valvular stenosis, or both.
OTHER: With right-sided congestive heart failure, jugular distension with or without jugular pulsation, cool extremities, dyspnea, hepatomegaly, and/or ascites may be apparent on physical examination.

Breeding advice:

Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening, and their offspring should be evaluated thoroughly (echocardiography).

One obstacle to controlling tricuspid valve disease in the dog population in general and in specific breeds in particular is that overt symptoms are generally not evident until after a dog has reached breeding age. However, a heart murmur can often be detected long before the onset of symptoms. Breeders are encouraged to select mature rather than young dogs for breeding, and to use them only once they have been certified free of murmurs, preferably by a veterinary cardiologist (see www.acvim.org or www.ecvim-ca.org for directories of veterinary cardiologists in North America and Europe, respectively).
There is widespread agreement regarding echocardiography (cardiac ultrasound) for dogs that have murmurs: only by having an echocardiogram is it possible to tell whether the murmur comes from tricuspid dysplasia or any of dozens of other defects, many of which are harmless. However, controversy exists regarding whether all Labrador dogs, with or without heart murmurs, should have an echocardiogram at some point in their lives prior to being used for breeding. The advantage is the opportunity to identify "silent" (no murmur) tricuspid dysplasia and reduce its transmission through the gene pool; the drawback is the time and cost needed to have an ecocardiogram performed.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Wright KN. Tricuspid valve dysplasia. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed. (St. Louis, MO: Mosby Elsevier, 2011) pp. 1117-1119.

Adin DB. Tricuspid valve dysplasia. In Bonagura JD, Twedt DC, eds. Kirk's Current Veterinary Therapy XIV (St. Louis, MO: Saunders Elsevier, 2008) pp. 762-765.

Ventricular septal defect (VSD)

roblib — Tue, 30 Mar 2010 16:31:35 +0000

What is ... ?:

A ventricular septal defect is a hole ("defect") in the muscular wall inside the heart (the septum) that separates the two main pumping chambers of the heart: the right ventricle and the left ventricle.

Before birth, the heart starts out as a single tube which gradually differentiates into 4 chambers during normal growth of the fetus in the dam (mother). Abnormalities can arise at several steps in the process, resulting in defects in the muscular walls that normally separate the heart into the right and left atria, and the right and left ventricles. The result is abnormal blood flow in the heart with varying effects in a dog, depending on the size and location of the defect.

How is ... inherited?:

In the English bulldog and keeshond, inheritance is autosomal recessive, with variable expression. This means that either one of the parents can pass along the gene to its offspring; one normal parent and one parent with the genetic defect that causes VSD is enough to transmit the condition to offspring, usually to varying degrees. That means that a dog with a small, insignificant VSD may produce puppies with a similarly small VSD, a large and severe VSD, or sometimes no VSD at all (a type of carrier state where the problem may then arise in subsequent generations).

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

The extent to which a dog will be affected by this defect depends on the size and location of the VSD inside the heart. Many dogs with VSDs have small defects that may not cause any problems and are entirely compatible with a normal lifespan.
Interestingly with VSD, the dogs with the smallest, least harmful defects are often the dogs with the loudest -not softest- heart murmurs. This means that having a loud heart murmur turn up during a veterinary exam, when the heart is checked (ausculted) using a stethoscope, is not automatically a serious problem. Rather, a heart murmur should be investigated further to determine whether a VSD is present (see below), and if so, how severe the condition is.
With larger VSDs, the circulation is disrupted in a way that forces the heart to work much harder. In some individuals this can be tolerated without causing symptoms for a long time (months to years) but in others, life-threatening symptoms are possible even at an early age.

Signs or symptoms associated with this disorder may develop within months or years, depending on the size of the defect, and they include shortness of breath and exercise intolerance. Rarely, collapse and cardiac arrest may occur in a dog with a VSD, especially if the defect is large and the dog is physically overactive. A veterinarian can monitor the condition of the VSD and the heart in an affected dog and recommend treatment, or consultation with a veterinary cardiologist, as required. Treatment may include medications to support the heart and to reduce congestion in the lungs, a special diet, and exercise restriction, but unlike in humans, repair of the defect is rarely performed because it would usually require open-heart surgery.
Among puppies with large VSDs, it is probable that many die early, before 8 weeks of age or before they are examined by a veterinarian. For this reason, stillborn puppies or pups that die very young (before weaning) should be autopsied, because the assumption of "fading puppy" or "runt of the litter" as the cause of death often misses the point: the cause of death may have been a severe heart malformation like a large VSD, and knowing whether or not this is the case can be vital for future breeding decisions.

How is ... diagnosed?:

Often, as with most heart defects, the first indication of a problem is when the veterinarian hears a heart murmur during a puppy's routine physical examination. Sometimes there is exercise intolerance or respiratory difficulty, but this is usually in an older dog or a young pup with a large defect. It is important to note that normal healthy puppies without VSDs may sometimes have heart murmurs too, for a few weeks as they are growing up. Therefore, if a veterinarian identifies a heart murmur, the best course of action may be to wait 2-3 weeks and recheck (because "innocent" murmurs that puppies outgrow should be gone after 2-3 weeks, whereas the murmur of a VSD would persist) or simply to have tests to confirm whether a VSD is present.

Diagnostic tests that are very helpful in this regard include thoracic radiographs (chest x-rays) and a cardiac ulstrosund (sonogram of the heart, echocardiogram).
If a VSD is identified, then the degree of severity and impact can be pinpointed, and the long-term implications discussed. A VSD may produce no strain on the heart at all (many people have VSDs and live normal lives with them) whereas other VSDs may become life-shortening, depending on the extent of the defect identified with tests.

How is ... treated?:

Overt symptoms caused by VSDs are treated when and if they develop. Treatments include medications to support the heart and to reduce pulmonary congestion, a special diet if medications are being given, and exercise restriction. None of these forms of treatment is useful (and some may be detrimental) if overt symptoms/signs referable to the VSD have not yet occurred.

Two surgical options exist but are used very seldom. Where a large VSD has been identified, but before right-to-left shunting has developed, pulmonary artery banding can be done to decrease the blood flow across the defect, thereby reducing the circulatory overload on the lungs and the left heart. Another procedure involves actual repair of the defect, via open-heart surgery. This procedure is performed in fewer than 10 veterinary centers worldwide and carries a high risk; a veterinarian can help determine whether an individual dog is a suitable candidate for either of these procedures.

For the veterinarian:

MURMUR: harsh regurgitant holosystolic murmur, loudest in *right* intercostal spaces 2 to 4; also can often be heard cranially on left thorax. The differential diagnosis for systolic murmurs that are loudest on the right side of the thorax is very limited (VSD, tricuspid regurgitation, subaortic stenosis in some cases).
ELECTROCARDIOGRAM: normal or suggestive of LV enlargement (with larger shunts; R waves > 2.5 mV in lead II); may suggest right-sided enlargement if right-to-left shunt develops (rare). Not definitive for diagnosis of VSD but may identify some secondary changes that are consistent.
RADIOGRAPHS: normal or left-sided enlargement; with larger shunts, increased prominence of pulmonary vasculature ("overcirculation"); right-sided enlargement if right-to-left shunt develops.
ECHOCARDIOGRAM: Diagnostic test of choice for confirming VSD and identifying secondary changes (if any) and concurrent defects (if any).
OTHER: Clinical signs usually only occur if the pulmonary vascular volume is more than 2 to 3 times normal, which requires a defect of medium to large dimensions. Most commonly, if signs occur, they are associated with a left-to-right shunt and signs of left-sided congestive heart failure are seen. Where secondary obstructive pulmonary vascular disease develops, so that pulmonary resistance exceeds that of the systemic vasculature, a right-to-left shunt develops (Eisenmenger's physiology). This is associated with cyanosis and polycythemia and generally carries a guarded prognosis, although dogs that are quiet housepets may have an acceptable quality of life in a calm household.

Breeding advice:

Affected pups and their parents (assumed to be carriers) should not be bred. Siblings that appear normal after careful physical examination may be used for breeding with caution. Their offspring should be carefully examined and, if affected, the breeding of the parents should be discontinued.

Resources:

Oyama MA, Sisson DD, Thomas WP, Bonagura JD. Congenital heart disease. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Elsevier Saunders, 2010) pp. 1250-1298.
O'Sullivan ML. Ventricular septal defect. In Cote E, ed. Clinical Veterinary Advisor: Dogs and , 2nd ed (St. Louis, MO: Elsevier Mosby, 2011) pp. 1168-1169.

Persistent right aortic arch ( vascular ring anomaly )

roblib — Mon, 07 Jun 2010 08:18:55 +0000

What is ... ?:

The term vascular ring anomaly describes several disorders that occur because of abnormal development of the major blood vessels in the chest. Malformations in these arteries may entrap vital structures, or may be harmless differences that never hamper a dog's health. The most common abnormality is a persistent right aortic arch which develops instead of the left aortic arch that would normally become the permanent aorta, the main blood vessel leading from the heart. It causes varying degrees of narrowing of the esophagus, leading to digestive problems in weanling puppies.

These anomalies are relatively common in puppies. They do not cause problems in the circulation of blood around the body; however, entrapment of the esophagus and sometimes the trachea can cause regurgitation, unthriftiness, and often aspiration pneumonia.

How is ... inherited?:

Inheritance is complex. This means a single genetic defect has not been identified that explains all cases, and a genetic test does not yet exist.

What breeds are affected by ... ?:

What does ... mean to your dog & you?:

Signs of this condition usually become apparent shortly after weaning, when a puppy begins eating semi-solid or solid food. The partial obstruction of the esophagus causes regurgitation, which is a passive reflux of undigested food, often in a tubular shape, back out the mouth. Dogs with this condition are often excessively thin or even emaciated, and yet often have ravenous appetites. They are prone to aspiration pneumonia, meaning that they may choke on regurgitated food and become ill as a result of inhaled mucus, food, and water.
Vascular ring anomalies like persistent right aortic arches can be corrected surgically. It is important to do so promptly, to reduce the likelihood of permanent damage to the esophagus. Vascular ring anomalies are never outgrown: they cannot self-correct spontaneously.

How is ... diagnosed?:

This condition is suspected when a puppy first begins regurgitating within a few days of weaning. It is important to note that regurgitation, which is a passive process, is different from vomiting, which is an active process. Regurgitation involves the puppy producing undigested food and mucus through the mouth with no effort; the pup tilts its head down and the food and mucus simply roll out. This is typical of vascular ring anomalies/persistent right aortic arch if it first occurs just after weaning. By contrast, vomiting is an active process, meaning there are abdominal contractions ("heaving") and a retching noise when food and mucus are expelled out the mouth. Vomiting is not a symptom of vascular ring anomalies. The distinction between regurgitation and vomiting is important because vascular ring anomalies/persistent right aortic arch only ever cause regurgitation, whereas dozens of disorders may cause a pup to vomit.
Chest x-rays are the confirmatory test of choice. The deviation of certain vital structures, notably the trachea, on X-ray, is conclusive in virtually all cases. Feeding an X-ray dye called barium was formerly thought to be essential for confirming persistent right aortic arch but is now known to be essentially obsolete.
Chest X-rays also help differentiate vascular ring anomaly/persistent right aortic arch from juvenile diffuse megaesophagus, which is a generalized weakening of the esophagus that many puppies simply outgrow without treatment.
There is no benefit to performing echocardiography (cardiac ultrasound), electrocardiography (ECG/EKG), or other tests of the cardiovascualr system, unless the veterinarian suspects an additional, unrelated heart problem. Vascular ring anomalies alone do not cause abnormalities on echocardiograms or ECGs.

How is ... treated?:

Correcting vascular ring anomalies/persistent right aortic arches requires surgery. The operation consists of a thoracotomy (opening the chest) and ligation and transection of the ligamentum arteriosum, the most accessible component of the ring constricting the esophagus. Surgery should be performed as early in a puppy's life as possible, to reduce the likelihood of permanent damage to the esophagus due to chronic distension.
Postoperative care involves feeding a liquid diet with the puppy held upright in a sitting position for some time after feeding, to help the liquid diet pass down to the stomach. After days to weeks, solid food is gradually reintroduced in the form of frequent small meals. In some dogs occasional regurgitation may persist despite surgery, but even in these cases, dogs tend to do much better than if they had not had surgical correction.

For the veterinarian:

Confirmation of persistent right aortic arch is best obtained with a dorsoventral or ventrodorsal radiographic projection of the thorax, which identifies leftward deviation of the trachea just cranial to the heart base. Barium esophagrams are virtually never required (see both references, below).

Breeding advice:

Affected individuals and their parents should not be used for breeding. Siblings should only be used after careful screening. If any affected offspring are born, breeding of the parents probably should be discontinued, although test breeding and close monitoring of offspring may be considered.

FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.

Resources:

Buchanan, J.W. 2004. Tracheal signs and associated vascular anomalies in dogs with persistent right aortic arch. Journal of Veterinary Internal Medicine; 18 (4): 510-514.
Adin D.B., Adin C.A. 2011. Vascular ring anomaly. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd edition (St. Louis, MO: Elsevier Mosby) pp. 1160-1162.
Patterson, D.F. 1996. The genetics of canine congenital heart disease. ACVIM-Proceedings of the 14th Annual Veterinary Medical Forum: 225-226.

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Arrhythmogenic right ventricular cardiomyopathy (ARVC) (Boxer cardiomyopathy)

roblib — Fri, 29 Apr 2011 12:20:15 +0000

What is ... ?:

Arrhythmogenic right ventricular cardiomyopathy, also called Boxer cardiomyopathy or familial ventricular arrhythmias of Boxers, is a type of heart disease that causes an erratic and potentially unstable heartbeat (arrhythmia). It occurs almost exclusively in the Boxer breed, and generally only in adult/older dogs. The characteristic finding is a specific type of premature heartbeat originating from the ventricles of the heart, called premature ventricular complexes or ventricular tachycardia. These are best identified on an electrocardiogram (ECG, EKG) or a portable heart monitor (Holter or event monitor).

How is ... inherited?:

The disorder is believed to be inherited as an autosomal dominant trait with variable penetrance, meaning it may be transmitted by the sire or the dam, and the extent to which offspring are affected is individually variable. Males and females are affected equally. No coat colour is associated with a higher or lower likelihood of developing arrhythmogenic right ventricular cardiomyopathy.

What breeds are affected by ... ?:

Boxer

What does ... mean to your dog & you?:

Arrhythmogenic right ventricular cardiomyopathy can be suspected in one of three different situations:
1- On a routine checkup, or during electrocardiographic (ECG) monitoring for anesthesia, the characteristic heartbeat irregularity is identified by the veterinarian; or
2- A dog develops episodes of stumbling, collapse, and/or loss of consciousness, and evaluation by the veterinarian reveals the typical cardiac arrhythmia on ECG; or
3- Arrhythmogenic right ventricular cardiomyopathy can be life-threatening, and occasionally there are no symptoms until a dog dies suddenly; an autopsy then identifies that arrhythmogenic right ventricular cardiomyopathy was the cause.
Whether overt symptoms are present or not, arrhythmogenic right ventricular cardiomyopathy is a nonpainful type of heart condition that tends to worsen over time. Daily oral medications can be given at home to reduce the frequency and severity of symptoms if they are occurring, and dogs may live well for weeks, months, or occasionally years with arrhythmogenic right ventricular cardiomyopathy when they respond well to medications.

How is ... diagnosed?:

Arrhythmogenic right ventricular cardiomyopathy is confirmed using an electrocardiogram (ECG) to identify the characteristic irregular heartbeat (arrhythmia). Since arrhythmias occur for many different reasons, standard blood and urine tests and medical screening (chest X-ray, ultrasound exam of the heart and the abdomen) are appropriate to identify other problems that are completely different but could be mimicking arrhythmogenic right ventricular cardiomyopathy. In this way, arrhythmogenic right ventricular cardiomyopathy can be considered a diagnosis of exclusion: eliminating all other possibilities leaves it at the most likely remaining explanation. Final confirmation is always possible at autopsy, where microscopic evaluation of the tissue of the right ventricle of the heart typically shows that it is infiltrated with abnormal fibrofatty tissue.

How is ... treated?:

Arrhythmogenic right ventricular cardiomyopathy is a genetically-transmitted disorder and as such, the underlying cause cannot be reversed. Medications are used for stabilizing the rhythm of the heartbeat (including such antiarrhythmics as sotalol, for example) and for offsetting some of the process of cardiomyopathy (such as with omega-3 fatty acids). These treatments are oral medications that can be given at home, and a good response to treatment consists of a decrease or disappearance of symptoms. The medications can provide a normal quality of life and this may continue for weeks, months, or occasionally years in dogs who respond well to treatment.

For the veterinarian:

ELECTROCARDIOGRAM: This is the diagnostic test of choice for arrhythmogenic right ventricular cardiomyopathy. The characteistic finding is premature ventricular complexes (PVCs) and/or ventricular tachycardia (VT). The premature complexes are typically of right ventricular origin, meaning a positive polarity in leads I, II, and aVF.
COMPLETE BLOOD COUNT, SERUM BIOCHEMISTRY PROFILE, URINALYSIS: Results should be within normal limits, excluding other causes of PVCs/VT.
THORACIC RADIOGRAPHS: Results should be within normal limits, excluding other causes of PVCs/VT.
ECHOCARDIOGRAM: Results should be within normal limits, excluding other causes of PVCs/VT. This is a type of cardiomyopathy that rarely alters the physical structure of the heart in an echocardiographically-apparent way.
ABDOMINAL ULTRASOUND: Results should be within normal limits, excluding other causes of PVCs/VT.
Some hospitals are equipped to assess serum cardiac troponin-I levels (human assay works equally well for dogs), and these are very often increased in arrhythmogenic right ventricular cardiomyopathy of Boxer dogs.

Breeding advice:

Boxers with arrhythmogenic right ventricular cardiomyopathy should not be bred. Current standards include screening potential breeding stock using Holter monitoring; a specific cutoff remains elusive, but generally dog with <100 PVCs/24 hours are considered fit to breed and dogs with >1000 PVCs/24 hrs should not be bred. The intermittent and highly variable nature of PVC occurence means that annual follow-up of beeding animals is very important, as is close evaluation of offspring if an adult later is found to have developed arrhythmogenic right ventricular cardiomyopathy after initially having been cleared on earlier screening.

Resources:

Spier AW. Arrhythmogenic right ventricular cardiomyopathy, dog. In Cote E, ed. Clinical Veterinary Advisor: Dogs and Cats, 2nd ed (St. Louis, MO: Mosby Elsevier, 2011) pp. 90-93.
Meurs KM. Myocardial disease: canine. In Ettinger SJ, Feldman EC, eds. Textbook of Veterinary Internal Medicine, 7th ed (St. Louis, MO: Saunders Elsevier, 2010) pp. 1320-1328.

Mitral/tricuspid regurgitation due to myxomatous heart valve disease (page under development)

roblib — Thu, 12 Jan 2012 18:33:57 +0000