Atrioventricular muscle dystrophy
The disease results in the replacement of cardiomyocytes with fibrous tissue, initially at the atria. This causes the atria to be unable to depolarize and mechanically contract. As a result, cardiac contractions are driven solely from ventricular escape beats that originate from the ventricular subsidiary pacemaker site.
Affected dogs usually present at 1 - 3 years of age with a history of intermittent lethargy, weakness, syncope, coughing episodes and decreased appetite.
There may also be muscular dystrophy of facial and shoulder muscles.
Diagnosis is usually based on historical evidence of heart disease, radiographic or CT imaging evidence of generalized cardiomegaly and cardiogenic pulmonary edema and ECG findings.
Electrocardiogram usually reveals persistent atrial standstill (absence of a P wave) and bradycardia with a regular ventricular rhythm that is not alleviated by atropine administration or exercise.
An antemortem definitive diagnosis is difficult without histological examination of heart tissue.
Treatment includes pacemaker implantation and management of congestive heart failure with furosemide and benazepril, which may prolong the lifespan from 6 months to 2 years. Theophylline is often used as adjunct therapy in an effort to increase heart rate.
Affected dogs usually die of congestive heart failure due to myocardial failure despite treatment.
- Lai SR (2009) Atrioventricular muscular dystrophy in a 5-month-old English springer spaniel. Can Vet J 50(12):1286-1287
- Holland CT et al Dyserythropoiesis, polymyopathy, and cardiac disease in three related English springer spaniels. J Vet Int Med 5:151–159
- Tilley LP (1979) Essentials of Canine and Feline Electrocardiography. St. Louis, Missouri: Mosby. pp:144–145