Veterinary Clinics of North America: Small Animal Practice
Review articleBoxer dog cardiomyopathy: an update☆
Section snippets
Arrhythmogenic right ventricular cardiomyopathy
Careful evaluation of the disease by these investigators as well as others has demonstrated that boxer dog cardiomyopathy has striking similarities to a human myocardial disease called arrhythmogenic right ventricular cardiomyopathy (ARVC) [4], [5]. ARVC is an inherited disorder that is characterized by fatty or fibrofatty replacement of right and, sometimes, left ventricular myocardium. Ventricular tachycardia, which often exhibits an upright or left bundle branch configuration, is a common
Cause
ARVC in the Boxer dog is a familial disease apparently inherited as an autosomal dominant trait [5]. The presentation of the disease in affected offspring is quite variable, however, suggesting that incomplete penetrance of the disease may be involved. Affected dogs may experience lethal ventricular arrhythmias and sudden cardiac death, may develop systolic dysfunction and congestive heart failure, or may live an asymptomatic life with frequent ventricular ectopy.
Clinical presentation
Boxer ARVC is an adult-onset myocardial disease and, as originally proposed by Harpster, there seems to be three forms of the disease, now referred to as concealed, overt, and myocardial dysfunction [1]. The concealed form is characterized by an asymptomatic dog with occasional ventricular premature complexes (VPCs). The overt form is characterized by a dog with tachyarrhythmias and syncope or exercise intolerance. The third group, diagnosed least frequently, is characterized by a dog that has
Diagnosis
The diagnosis of canine ARVC can be challenging. Unfortunately, a single diagnostic test for ARVC does not exist. The diagnosis is best based on the presence of a combination of factors, including a family history of disease, the presence of a ventricular tachyarrhythmia, a history of syncope or exercise intolerance, and the postmortem finding of fibrofatty infiltration into the myocardium.
Screening
The familial nature of ARVC has led to increased interest by Boxer breeders in the screening of breeding dogs for the disease. Unfortunately, because of the absence of a perfect diagnostic test for ARVC, screening the asymptomatic dog is challenging, and substantial efforts are being directed toward the development of a genetic test. Careful consideration of multiple criteria should be used to help determine the likelihood that an individual asymptomatic dog is affected. Important factors might
Treatment
Treatment considerations for affected dogs are generally directed toward the use of ventricular antiarrhythmics, because most affected dogs do not have systolic dysfunction and do not seem to progress to heart failure. When prescribing antiarrhythmics for the affected dog, several considerations should be taken into account. There are known benefits to the use of certain antiarrhythmics in affected dogs, including the ability to decrease the number of VPCs and the complexity of the arrhythmia.
Prognosis
Dogs with ARVC are always at risk of sudden death. Many affected dogs live for years even without treatment, however. Many dogs may be managed, symptom free, for years on antiarrhythmics. A small percentage of these dogs may eventually develop ventricular dilation and systolic dysfunction.
l-carnitine cardiomyopathy in Boxers
A deficiency in myocardial l-carnitine levels was observed in a family of Boxers with left ventricular dilation and systolic dysfunction. The tachyarrhythmias included atrial fibrillation and VPCs. The dogs had normal to high levels of plasma l-carnitine but low levels of myocardial carnitine. Supplementation with l-carnitine as well as standard heart failure therapy resulted in significant improvement in myocardial function and clinical condition but did not result in total regression of the
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This work was generously supported by the American Kennel Club–Canine Health Foundation and the American Boxer Trust.