Arrhythmogenic right ventricular cardiomyopathy (ARVC) occurs primarily in Boxers and is also known as "Boxer cardiomyopathy." ARVC rarely occurs in cats. It is characterized by a fatty or fibrofatty infiltrate of the right ventricular myocardium due to a mutation in a gene that encodes for striatin, a desmosomal protein. A test is commercially available to identify the mutation. The most common clinical sign of the disease is syncope that is due to a very fast (> 400 bpm), nonsustained ventricular tachycardia. It takes 6–8 seconds of no blood flow to the brain to result in unconsciousness, so the tachycardia must last that long for syncope to occur and then must stop spontaneously for sudden death not to occur.
The diagnosis of ARVC is based on the number of premature ventricular contractions (PVCs) on a Holter monitor (> 100–300 PVCs in 24 hours is generally considered diagnostic of ARVC in Boxers) or on the presence of ventricular tachycardia. The heart looks normal on thoracic radiographs and on echocardiograms in most Boxers with ARVC; some (approximately 10% in the US), however, will develop true dilated cardiomyopathy and go into heart failure. Approximately 90% of Boxers with DCM have the striatin gene mutation, and being homozygous for the mutation is a risk factor for developing DCM. Boxers presented for syncope without DCM are treated with sotalol (1–3 mg/kg, PO, every 12 hours) or a combination of mexiletine (5–10 mg/kg, PO, every 8 hours) and atenolol (12.5–25 mg/dog, PO, every 12 hours).In cases where sotalol is ineffective, the dog may be administered mexiletine as well. For Boxers with ARVC that do not have DCM, the prognosis is often good, and many live for several years on antiarrhythmic treatment. The longterm prognosis for dogs with DCM that are in heart failure is poor. Most live only several months.
In cats, ARVC usually manifests as severe right ventricular and atrial enlargement and right heart failure, typically along with some supraventricular and ventricular tachyarrhythmias. Dyspnea and tachypnea due to pleural effusion, ascites, and nonspecific clinical signs such as anorexia and lethargy are reported in affected cats. Treatment is similar to that for DCM. Longterm prognosis is generally poor.
