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 the 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 catheter and a micromanometer in 7 anesthetized mongrel dogs. We assessed preload by the end-diastolic volume, afterload by the effective arterial elastance, and left ventricular contractile properties by the slope of the end-systolic pressure–volume relationship. In addition, optimal ventricular arterial coupling (ratio of effective arterial elastance to slope of end-systolic pressure–volume relationship) and left ventricular work efficiency (ratio of external work to pressure–volume area) were calculated. Results. The decrease in preload was much greater with LHB than venoarterial bypass. There were no significant differences in afterload and left ventricular contractility between venoarterial bypass and LHB. The ventricular arterial coupling during LHB was near 0.50 (0.69 ± 0.16) in the “best heart” condition (effective arterial 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 left ventricular performance after cross-clamping of the descending thoracic aorta.