Cardiac energy considerations during intraaortic balloon pumping

Abstract

Cardiac oxygen availability and oxygen consumption were used in a theoretical study as indexes of myocardial energy supply and utilization, respectively. A detailed computer simulation of the closed-loop canine cardiovascular system was utilized to study the dependence of these indexes on timing of the intraaortic balloon pump. Oxygen availability exhibited higher sensitivity to balloon timing than oxygen utilization. While maximum augmentation of oxygen availability was 58 percent, oxygen consumption could be reduced by only 13 percent. Animal experiments were initiated to validate the theoretical results. The results of both the animal experiments and the computer simulation suggested that neither balloon timing which maximizes oxygen availability nor timing which minimizes oxygen consumption correlates with timing which minimizes aortic end diastolic pressure. Thus, end diastolic pressure, presently used as a determinant of proper timing in patients undergoing cardiac assistance, was found to be a poor index of ventricular energy consumption. A performance index comprised of clinically available variables, was formulated to reflect myocardial energy balance. In this performance index, mean diastolic pressure was used to represent energy availability and peak systolic pressure was used as an index of oxygen consumption. Their relationship to oxygen balance and their dependence on timing were studied using the computer simulation of the canine cardiovascular system and animal experiments. Theoretical and experimental results suggest that such an index is capable of representing O2 balance and can be used to control phasing of the device.

Intra-aortic Balloon Pump Timing: Review of Evidence Supporting Current Practice

“…Schreuder et al 4 confirmed the findings of Cheung et al, 9 showing that an IABP reduced left ventricular end-systolic pressure and volume, improved stroke volume, reduced left ventricular stroke work (LVSW), and reduced left ventricular end-diastolic pressure and volume. In contrast to Barnea et al, 5 Schreuder et al 4 and Cheung et al 9 concluded that afterload reduction was the primary mechanism by which an IABP improved left ventricular performance immediately (within 20 seconds), because improvement in coronary flow cannot occur within that time, and that therefore an IABP is critically important in heart failure patients without ischemia. I ntra-aortic balloon counterpulsation (IABC) is the most widely used form of left ventricular mechanical support today; more than 160 000 patients worldwide receive this therapy annually.…”

“…Schreuder et al 4 were the first to show the effect of timing on left ventricular dyssynchrony and concluded that early inflation is the worst timing error, reducing both left ventricular performance and IABP efficacy. Although late inflation has not been studied, several investigators 3,5,6 have concluded that late inflation reduces augmentation time and coronary artery perfusion pressure.…”

“…Research on conventional deflation timing is less compelling than that on inflation timing; several studies 5,17,18 show the immediate and beneficial effect of properly timed use of intra-aortic balloon counterpulsation on left ventricular function. The effect of the intra-aortic balloon pump is seen on the first beat of counterpulsation (1) and has reached its full effect within 4 beats.…”

“…Changes in mean diastolic pressure were predictive of more than 85% of the increase in coronary flow. 5,6 Kern et al 7 found that IABPs unequivocally increased coronary flow in the proximal part of coronary arteries with less than 50% stenosis and in patients who had successful revascularization procedures. Hypotensive patients experienced the most significant improvement, with coronary flow increases of greater than 100% during IABP inflation.…”

“…Barnea et al 5 found that because IABC reduces myocardial oxygen demand, the left ventricle can continue to function adequately during periods of reduced oxygen supply. Figure 2 shows how oxygen supply and demand are balanced by IABC through the improvement in the endomyocardial viability ratio, allowing the left ventricle to heal and often recover from ischemia-related injuries.…”