Hypertrophic cardiomyopathy, defined as inappropriate myocardial hypertrophy of a nondilated left ventricle, may occur in the absence of an identifiable stimulus for the hypertrophy (congenital) or secondary to other cardiac abnormalities such as mitral valve dysplasia.
Functionally, HCM results in dynamic left ventricular outflow tract obstruction and reduced diastolic filling.
This disease has been more commonly observed in older Rottweiler and Dalmatian breeds, although a wide range of ages and breeds are affected, where anesthetic risks with this condition are considered high due to development of intraoperative hypotension.
Clinical signs are often absent, but a systolic heart murmur or arrhythmia may be detected on auscultation.
Echocardiography in older dogs with chronic hypertrophic cardiomyopathy usually show signs of thickened mitral valve, left atrial enlargement, excess motions of the left ventricular free wall and the ventricular septum, and tricuspid, mitral and aortic valve regurgitation.
A definitive diagnosis unfortunately requires postmortem examination of the heart, which usually shows left ventricular and interventricular septal hypertrophy of equal magnitude, with impact lesion and plaques on the interventricular septum. The mitral valve has often migrated into the left ventricular outflow tract.
Histologically, one usually observes intimal hyperplasia, hypertrophy, and smooth muscle hyaline degeneration of coronary arteries as well as focal myocardial necrosis, fibrosis, and dystrophic calcification.
A differential diagnosis would include ventricular septal defect, double-chambered right ventricle, hyperthyroidism, arrythmogenic right ventricular cardiomyopathy, endocardial amyloidosis, endocarditis, mitral valve endocardiosis, other causes of congestive heart failure and infections with Dirofilaria spp.
A possible association with canine parvovirus infection has been postulated by not proven, and seems unlikely due to the absence of any microscopic inflammatory disease associated with this condition.
Surgical correction can be performed at specialty referral centers via balloon valvuloplasty.
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