Hypertrophic cardiomyopathy in the dog.

Clinical and necropsy findings in 10 dogs with a spontaneous primary hypertrophic cardiomyopathy are described. Each dog had marked cardiac hypertrophy, and 8 dogs had disproportionate thickening of the ventricular septum with respect to the left ventricular free wall (compared with dogs with normal hearts or with cardiac hypertrophy due to acquired or congenital heart disease). Septal:free wall thickness ratios in the 10 dogs ranged from 1.1 to 1.5; 6 had ratios greater than or equal to 1.3. However, marked cardiac muscle cell disorganization in the ventricular septum, characteristic of patients with hypertrophic cardiomyopathy, was present in only 2 of the 10 dogs. Death occurred most commonly while the dogs were under anesthesia during the course of operative procedures (5 dogs) or suddenly and unexpectedly in animals without previous symptomatic manifestations of cardiac disease (3 dogs). Four dogs had clinical signs of congestive heart failure, including 2 with marked cardiac decompensation. In addition, 2 of these 4 dogs with heart failure and 1 dog without previous symptoms (that died during a noncardiac operation) manifested complete heart block. It is conceivable that dogs with spontaneous hypertrophic cardiomyopathy may prove useful in the future investigations of the clinical, hemodynamic, and pathologic features of this disease in humans.