Functional and Morphologic Pathology of Equine Aortic Insufficiency

Twelve horses and 3 mules with grade II or louder prolonged diastolic murmurs were selected for functional and histopathologic study. Aortic insufficiency was demonstrated in all mules and in all except two horses on the basis of murmurs, jet lesions and/or pathologic and incompetent valve cusps. In 15 control animals lesions resulting in aortic insufficiency were not found. A thick fibrous band was present on all aortic valve cusps judged to be definitely insufficient. This band occurred at the line of valvular closure, parallel to the free edge, and allowed eversion of the peripheral portion of the cusp. Endothelial covered villi were present on the ventricular surface of those valves with band lesions. There was fibroblastic proliferation in a rich ground substance within the villi, on the surface of the ventricularis and throughout all layers of the valve. A nodular lesion microscopically similar to nonbacterial thrombotic endocarditis in man was also found on the ventricular surface. This lesion also involved all layers of the aortic leaflet with proliferation of fibrocytes and production of acid mucopolysaccharide ground substance and collagen fibers. The nodular lesions did not appear to contribute significantly to the insufficiency. Degeneration of elastic fibers and focal mineralization of the fibrosa were interpreted as senile degenerative changes.