Ultrastructure of crista supraventricularis muscle in patients with congenital heart diseases associated with right ventricular outflow tract obstruction.

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Abstract
Ultrastructural studies were made of operatively resected crista supraventricularis muscle in 59 patients with congenital heart diseases, or whom 54 had obstruction to right ventricular outflow. Relationships of anatomic diagnosis, age, peripheral arterial oxygen saturation (PAO2), peak right ventricular systolic pressure gradient and right ventricular end-diastolic pressure (RVEDP) to hypertrophic changes, abnormalities of cellular and myofibrillar orientation, and degenerative alterations were determined. Changes directly related to hypertrophy were: cell diameters greater than 20 mu, irregular cell shape, lobulated nuclei, multiple intercalated discs, dilated T tubules, abnormal Z bands, and increased numbers of ribosomes. Abnormalities of cellular or myofibrillar orientation were focal in distribution and occurred in 12 patients, most of whom had elevated RVEDP, decreased PAO2, markedly enlarged cells, and interstitial fibrosis. Interstitial fibrosis was prominent in 19 patients and was associated with cellular hypertrophy, elevation of RVEDP, and increased age of the patients. Degenerative changes (myofibrillar lysis, abnormally small mitochondria, myelin figure formation, and proliferation of sarcoplasmic reticulum in cardiac muscle cells ocurred in six patients and correlated with increased age, decreased PAO2, and elevated RVEDP. Mitochondria containing glycogen deposits were present in 17 patients, most of whom had decreased PAO2. The variability of morphologic manifestations of chronic cardiac hypertrophy and the relationships of hypertrophic changes to orientation abnormalities and degenerative alterations are discussed.