Arrhythmogenic right ventricular cardiomyopathy (ARVC) (Boxer cardiomyopathy)

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 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.


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