Comparison of the distribution of intramyocardial pressure across the canine left ventricular wall in the beating heart during diastole and in the arrested heart. Evidence of epicardial muscle tone during diastole.

Abstract

Computations of compliance of the left ventricle (LV) during diastole assume passive tissue characteristics. Diastolic LV intramyocardial pressure was measured simultaneously in the subepicardium and subendocardium in 18 open-chest dogs, using 1-mm in diameter micromanometers. Subepicardial pressure, 26 .+-. 1 mm Hg (mean .+-. SEM [standard error of the mean]) exceeded subendocardial pressure, 14 .+-. 1 mm Hg (P < 0.001) and it exceeded left ventricular end-diastolic pressure (LVEDP) (9 .+-. 1 mm Hg) (P < 0.001). After an infusion of dextran-40 (10 dogs), subepicardial diastolic pressure increased to 42 .+-. 4 mm Hg which was higher than diastolic subendocardial pressure, 26 .+-. 2 mm Hg (P < 0.001) and LVEDP, 24 .+-. 2 mm Hg (P < 0.001). Following cardiac arrest (12 dogs) with the intramyocardial probes unchanged in position, LV intracavitary pressure, 9 .+-. 1 mm Hg, and subendocardial pressure, 13 .+-. 3 mm Hg, did not differ significantly from the pressures in the beating heart. Subepicardial pressure, 9 .+-. 1 mm Hg, was lower than in the beating heart (P < 0.001). Following distension of the arrested LV (12 dogs) subepicardial pressure, 31 .+-. 7 mm Hg, was lower than subendocardial pressure, 58 .+-. 12 mm Hg (P < 0.001) and LV intracavitary pressure, 54 .+-. 11 mm Hg (P < 0.001). Tone is maintained by the subepicardium during diastole; the LV wall does not appear to behave as a passive shell during ventricular filling.