Ultrastructural investigations of cardiomyopathy in the dog.

Eight dogs of the giant breeds with congestive cardiomyopathy were studied at necropsy and samples taken for examination with the electron microscope. Of the 8 dogs, 6 were male. There were 4 Irish Wolfhounds, 2 Great Danes, one Pyrenean and one Saint Bernard. Ages ranged from 6 months to 7 years and if the atypical 6-month-old is removed, the average age was 5 and a third years. Ultrastructural examination of myocardium from abnormal animals showed increases in intermyofibrillar spaces, lipofuscin granules, fat droplets and myelin figures, mitochondrial hyperplasia, disruption of myofibrils and thickening of Z bands. Although all the ultrastructural changes noted were non-specific, the degree of degeneration in cases of congestive cardiomyopathy appeared to be greater than that reported in cases with heart failure caused by other conditions. However, there was no obvious correlation between the length or severity of illness and the degree of ultrastructural damage in dogs with congestive cardiomyopathy. Similarly, there was no correlation between the duration of illness and the severity of the hypertrophy (measured by Z band thickening). As in man, no characteristic features peculiar to this condition were established.