Histological evaluation of transannular autografts of pericardium placed in the right ventricular outflow tract of dogs.

Autografts of pericardium were inserted as patches into incisions across the annulus of the pulmonary valve in 12 adult dogs and 12 pups. In order to accommodate for possible effects of pulmonary hypertension which pertains in many clinical circumstances, constricting teflon bands were placed around the main pulmonary artery in half of the animals. Samples of tissue from the patches were examined by light and scanning electron microscopy from 6 to 14 mth later. The eventual thickness of the insertion site of the patches was found to become 2-14 times greater than the initial autograft due to apposition of layers of collagenous tissue on the endocardial and epicardial surfaces of the autografts. Three pups showed small, angiographically undetected central aneurysms in their patches but the tissue in their base was 5 or more times thicker than control pericardium. Cartilaginous metaplasia was evident at the margins of 57% of the patches, necrotic remnants of parts of the autograft were evident in 38% and foci of dystrophic calcification in 24% of them. Whereas smooth muscle cells sometimes extended into the repair tissue (19%), elastic fibres were not present in the patches. Thus pericardial autografts in the right ventricular outflow tract seem unlikely to develop clinically significant abnormalities.