Myocardial oxygen consumption. Comparison between left atrial pulsatile synchronous and asynchronous bypass

This controlled study was undertaken to quantitate the effect of R-wave synchronization (counterpulsation) on myocardial oxygen consumption (MVO₂) as reflected by the tension time index (TTI) during pulsatile left atrial to aortic bypass. Pulsatile ventricular assist devices were implanted in eight anesthetized, fully hemodynamically instrumented animals. After baseline measurement of TTI, heart rate, cardiac output, mean aortic and left atrial pressures, pulsatile left atrial to aortic bypass was instituted. Measurements were then continuously recorded during both left atrial pulsatile synchronous (LAPS) and asynchronous (LAPAS) bypass periods of pumping. Heart rate and mean aortic pressure were controlled throughout the experiment. TTI = 1819 ± 95 mmHg-sec (control); 987 ± 127 mmHg-sec (LAPAS); and 763 ± 89 mmHg-sec (LAPS). The results indicate TTI, and therefore MVO₂, is reduced significantly from control levels by either LAPS or LAPAS bypass. However, R-wave synchonization (counterpulsation) offers no further benefit in reducing TTI over the less complex LAPAS or full-to-empty mode pumping.