Atrial Cardiomyopathy in an Adult Labrador Retriever Dog.

A 7-year-old castrated male Labrador retriever was examined for a 10-day history of weakness and syncope. Physical examination revealed bradycardia and a grade III/VI left apical systolic heart murmur. Electrocardiography demonstrated bradycardia, absence of P waves and an atrio-ventricular nodal escape rhythm. Echocardiography revealed marked biatrial enlargement. Thoracic radiographs showed no evidence of pulmonary edema. Routine plasma biochemistry and electrolytes, basal serum cortisol, total thyroxin concentration, and complete blood count were within normal limits. Serum cardiac troponin I concentration was moderately increased. Serological examinations for antibodies against vector-borne diseases were negative. A pacemaker was implanted one month after the initial presentation due to worsening of the dog's clinical condition despite medical treatment. The dog remained asymptomatic for 18 months but was then re-presented with a gastric dilatation volvulus and subsequently euthanized. Necropsy and histology of the heart yielded a diagnosis of atrial cardiomyopathy.