Atrioventricular muscle dystrophy

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Radiograph of a dog with atrioventricular muscular dystrophy, showing cardiomegaly, pulmonary vein distension and pulmonary edema[1]

Atrioventricular muscular dystrophy is a rare autosomal-recessive hereditary heart disease of dogs characterized by progressive heart failure.

The disease has been reported in the English Springer Spaniel, Old English Sheepdog, Labrador Retriever, Bernese Mountain Dog and mixed breed dogs[2].

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.

Radiographic changes may include generalized cardiomegaly and cardiogenic pulmonary edema[1] due to volume overload secondary to bradycardia (< 60 beats per minute).

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.

A differential diagnosis would include hyperkalemia, Golden Retriever Muscular Dystrophy, nemaline myopathy, polymyositis and Duchenne muscular dystrophy[3].

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.

References

  1. 1.0 1.1 Lai SR (2009) Atrioventricular muscular dystrophy in a 5-month-old English springer spaniel. Can Vet J 50(12):1286-1287
  2. Holland CT et al Dyserythropoiesis, polymyopathy, and cardiac disease in three related English springer spaniels. J Vet Int Med 5:151–159
  3. Tilley LP (1979) Essentials of Canine and Feline Electrocardiography. St. Louis, Missouri: Mosby. pp:144–145