EFFECT OF ASSISTED CIRCULATION ON LEFT-VENTRICULAR PERFORMANCE IN A CANINE MODEL

Background. Little is known about left ventricular performance during venoarterial bypass and left heart bypass (LHB) after cross-clamping t he descending thoracic aorta. We evaluated the effects of venoarterial bypass and LHB on ventricular load optimization and left ventricular work efficiency. Methods. We used the left ventricular conductance cat heter and a micromanometer in 7 anesthetized mongrel dogs. We assessed preload by the end-diastolic volume, afterload by the effective arter ial elastance, and left ventricular contractile properties by the slop e of the end-systolic pressure-volume relationship. In addition, optim al ventricular arterial coupling (ratio of effective arterial elastanc e to slope of end-systolic pressure-volume relationship) and left vent ricular work efficiency (ratio of external work to pressure-volume are a) were calculated. Results. The decrease in preload was much greater with LHB than venoarterial bypass. There were no significant differenc es in afterload and left ventricular contractility between venoarteria l bypass and LHB. The ventricular arterial coupling during LHB was nea r 0.50 (0.69 +/- 0.16) in the ''best heart'' condition (effective arte rial elastance = slope of end-systolic pressure volume relationship/2) , whereas the work efficiency during LHB was at maximum (0.73 +/- 0.12 ). Conclusions. We conclude that LHB has a more beneficial effect on l eft ventricular performance after crossclamping of the descending thor acic aorta. (C) 1998 by The Society of Thoracic Surgeons.