Distribution of pressure across the left ventricular wall in the beating and arrested heart: Evidence of epicardial muscle tone during diastole

Abstract

DISTRIBUTION OF PRESSURE ACROSS THE LEFT VENTRICULAR WALL IN THE BEATING AND ARRESTED HEART: EVIDENCE OF EPICARDIAL MUSCLE TONE DLIRING DIASTOLE Paul D. Stein, MD, FACC; Hani N. Sabbah, AS, Mario Marzilll, MD, Henry Ford Hospital, Detroit, Michigan Computations of compliance of the left ventricle (LV) assume passive tissue characteristics. To evaluate this assumption, LV intramyocardial pressure was measured simultaneously in the subepicardlum and subendocardium during diastole in 9 open chest dogs using 1 mm diameter micromanometers. Subepicardial pressure, 28 2 2 mm Hg, exceeded subendocardial pressure, 15 i 2 mm Hg, (P < .OOl) and it exceeded LV end-diastolic pressure (10 t .4 mm Hg) (P < ,001). Following an infusion of dextran-40, subeplcardial pressure increased to 42 + 4 mm Hg which was higher than both subendocardial pressure, 27 ? 3 mm Hg (P<.OOl) and LV end-diastolic pressure (25 ? 2 mm Hg) (P < .OOl). Following death of the animal, with the intramyocardial probes unchanged in position, LV pressure 10 f 1 mm Hg, and subendocardial pressure, 13 + 3 mm Hg, did not differ significantly from pressure in life. However, subepicardial pressure, 10 ? 1 mm Hg, was lower than in life (P < .OOl). Following distension of the arrested heart with dextran-40 introduced through a LV cannula, subepicardial pressU=f, 22 + '3 mm Hg, was lower than subendocardial pressure, 41 < 4 mm Hg, (P c.001) and LV pressure, 41 + i mm Hg (P < .OOl). These observations indicate that tone is maintained in the subepicardium during diastole, and the LV ~~11 does not behave as a passive homogenous shell during ventricular filling. Therefore, methods of evaluation of the diastolic properties of the LV that assume passive elastic mechanical properties of the walls fail to account for diastolic subepicardial muscle