LEFT-VENTRICULAR MECHANICS DURING SYNCHRONOUS LEFT ATRIAL-AORTIC BYPASS

The purpose of this study was to analyze left ventricular mechanics during asynchronous, pulsatile left atrial-aortic bypass before and after microsphere injection with the pressure-volume relationship. In 14 anesthetized Holstein calves, left ventricular pressure was measured with a micromanometer and ultrasonic dimension transducers measured left ventricular orthogonal diameters. Ellipsoidal geometry was used to calculate simultaneous left ventricular volume. Contractility index, pressure-volume area, external work, and potential energy were calculated during steady-state contractions. These measurements were repeated during pulsatile left atrial-aortic bypass. To induce heart failure, we injected microspheres into the left main coronary artery, and the protocol for baseline and pulsatile left atrial-aortic bypass was repeated. Despite the significant differences in the baseline contractility index (7.4 +/- 0.7 mm Hg/ml versus 4.7 +/- 0.5 mm Hg/ml) contractility index remained the same during pulsatile left atrial-aortic bypass in control and heart failure modes, respectively. Pulsatile left atrial-aortic bypass significantly decreased end-diastolic volume (22% and 17%), pressure-volume area (58% and 48%) and external work (74% and 69%, all p < 0.05) during control and heart failure measurements, respectively. However, it did not change end-systolic volume or potential energy. In conclusion, asynchronous pulsatile left atrial-aortic bypass did not affect left ventricular contractile state in either the normal or failing heart. Although decreased pressure-volume area accounts for the reduction in myocardial oxygen consumption, unchanged potential energy suggested a limited unloading of the ventricle.