Reduced volume fraction of myofibrils in myocardium of patients with decompensated pressure overload.

The relation between quantitative ultrastructural changes of the left ventricular (LV) myocardium and contractile function was studied in patients with chronic aortic stenosis (AS). The volume fractions of myofibrils, sarcoplasm and mitochondria in myocardial cells were determined by electron microscopic morphometry in small LV tissue samples of 19 patients with AS. Interstitial fibrosis was measured by light microscopic morphometry. Transmural biopsies of the LV free wall perfused by the anterior descending branch of the left anterior descending coronary artery (LAD) were obtained during aortic valve replacement. LV function was analyzed from preoperative rightand left-heart catheterization and angiography. Group 1 consisted of seven patients with ejection fractions (EFs) greater than 55% and mean left atrial pressure (LAP) less than 15 mm Hg. Group 2 consisted of 12 patients with EFs less than 55% and mean LAP greater than 15