Epicardial coronary artery fibromuscular dysplasia, myocardial infarction and sudden death in a dog.

A 4-year-old male Shih Tzu died suddenly with the only history being slight lethargy during the previous 2 days. Gross and histopathological examination of the heart revealed severe segmental stenosis of the epicardial coronary artery branches and extensive areas of acute myocardial necrosis interspersed with areas of fibrosis. The segmental coronary artery stenosis was due to smooth muscle and myofibroblast proliferation in the tunica media. The smooth muscle cells and myofibroblasts disrupted the internal elastic lamina and extended into the tunica intima. Thickening of the intima and media was accompanied by fibrosis, consistent with fibromuscular dysplasia. The resulting stenosis led to myocardial infarction and cardiac insufficiency. This report details for the first time the vascular lesions in a case of sudden cardiac death in a dog afflicted with fibromuscular dysplasia of the coronary arteries.