LEFT-VENTRICULAR MECHANICS DURING SYNCHRONOUS LEFT ATRIAL-AORTIC BYPASS

The purpose of this study was to analyze left ventricular mechanics du ring asynchronous, pulsatile left atrial-aortic bypass before and afte r microsphere injection with the pressure-volume relationship. In 14 a nesthetized Holstein calves, left ventricular pressure was measured wi th a micromanometer and ultrasonic dimension transducers measured left ventricular orthogonal diameters. Ellipsoidal geometry was used to ca lculate simultaneous left ventricular volume. Contractility index, pre ssure-volume area, external work, and potential energy were calculated during steady-state contractions. These measurements were repeated du ring pulsatile left atrial-aortic bypass. To induce heart failure, we injected microspheres into the left main coronary artery, and the prot ocol for baseline and pulsatile left atrial-aortic bypass was repeated . Despite the significant differences in the baseline contractility in dex (7.4 +/- 0.7 mm Hg/ml versus 4.7 +/- 0.5 mm Hg/ml) contractility i ndex remained the same during pulsatile left atrial-aortic bypass in c ontrol and heart failure modes, respectively. Pulsatile left atrial-ao rtic bypass significantly decreased end-diastolic volume (22% and 17%) , pressure-volume area (58% and 48%) and external work (74% and 69%, a ll p < 0.05) during control and heart failure measurements, respective ly. 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 th e reduction in myocardial oxygen consumption, unchanged potential ener gy suggested a limited unloading of the ventricle.