Comparative effect of counterpulsation and bypass on left ventricular myocardial oxygen consumption and dynamics before and after coronary occlusion

Mechanical Support of the Left Ventricle in Ischemia Induced Left Ventricular Failure: An Experimental Study

Objective

this study compares the hemodynamic effects of intraaortic balloon pumping (IABP), left ventricular assist device (LVAD), and extracorporeal membrane oxygenation (ECMO) in left ventricular failure in pigs.

Methods

In 29 pigs weighing 12 + 0.7 kg left ventricular failure was induced by ligating the left anterior descending coronary artery. Eight animals served as controls. Eight pigs were treated by IABP, seven by LVAD, and six by ECMO. The study period lasted four hours. Hemodynamic and oxygen transport/ uptake parameters were measured continuously or intermittently.

Results

Six animals of the ECMO and LVAD groups survived the 4 hour period, but only 3 and 4 animals of the IABP and control groups survived (p<0.05). Cardiac index decreased about 48% and 22% in the control and IABP groups (p<0.05), whereas there was only a slight decrease in the ECMO (9%) and LVAD (14%) groups. Oxygen delivery fell significantly in the control and IABP groups (p<0.05), compared with only a slight change in the LVAD and ECMO groups.

Conclusion

ECMO is the most effective system for temporary circulatory support in severe ventricular failure. LVAD maintains cardiac output when pulmonary blood flow is provided. IABP is less efficient in supporting the failing heart, especially in the presence of severe ventricular arrhythmias.

Ventriculoarterial coupling with intra-aortic balloon pump in acute ischemic heart failure

PURPOSE

We analyzed the mechanism of effects of intra-aortic balloon pumping using the pressure-volume relationship and ventriculoarterial coupling in the normal and failing hearts.

MATERIALS

In 12 anesthetized Holstein calves (weight, 94 +/- 8 kg), the ventricular end-systolic and arterial elastances, pressure-volume area, and external work were analyzed during steady-state contractions with traditional hemodynamic parameters with intra-aortic balloon pumping-off and -on (1:1 synchronous ratio). An acute ischemic heart failure was induced by injecting 10 microm microspheres (4.2 +/- 1.8 x 10(7). 100g left ventricular weight-1) into the left main coronary artery; all measurements were repeated.

RESULTS

Intra-aortic balloon pumping did not change hemodynamic parameters in the control. However, during heart failure, intra-aortic balloon pumping decreased the arterial elastance from 3.6 +/- 1.3 mm Hg to 2.9 +/- 1.2 mm Hg. mL-1 while not affecting the ventricular end-systolic elastance, this resulted in an improvement of the ventriculoarterial coupling ratio from 3.1 +/- 0.8 to 2.3 +/- 0.8. Intra-aortic balloon pumping decreased not only end-systolic pressure (from 69 +/- 16 mm Hg to 64 +/- 19 mm Hg) but end-diastolic volume and pressure (from 139 +/- 38 mL to 137 +/- 37 mL and from 13. 9 mm Hg to 12.8 mm Hg, respectively) with the leftward shift of the pressure-volume loop. Pressure-volume area decreased (from 914 +/- 284 mm Hg to 849 +/- 278 mm Hg. mL) although stroke volume increased (from 21 +/- 6 mL to 24 +/- 6 mL).

CONCLUSION

Reduction of the arterial elastance with intra-aortic balloon pumping improved the ventriculoarterial coupling ratio and increased stroke volume. Leftward shift of the pressure-volume loop resulted in the reduction of pressure-volume area, which suggests the conservation of the myocardial oxygen consumption.

Emergency bypass system: analysis of gas transfer

A portable emergency bypass system using a membrane oxygenator device (CPS) was evaluated. The ability of the CPS to supply the oxygen transfer needs of five anesthetized dogs consistently over six hours and the system's effects on hemoglobin concentration, platelet count, and degree of hemolysis were assessed. The animals maintained spontaneous heart beats, pump flows averaged 100 ml/kg/min; mean arterial pressures were maintained at from 114 to 144 mm Hg. Immediate dilution of hemoglobin and platelet levels occurred in the first 30 minutes. Further hemodilution was limited during the first two hours, although three of the animals required transfusions during the six-hour period to maintain their hematocrits. Plasma free hemoglobin did not significantly increase during the six hours. Baseline oxygen consumption data obtained in three animals ranged from 44.5 to 96 (ml oxygen/min/m2). Oxygen and carbon dioxide transfer measurements during the first hour of bypass were not significantly different from measurements during the last hour of perfusion. The study suggests that optimal use of the CPS could supply much if not all of a patient's basal oxygen transfer requirements for at least six hours.

Reduction of myocardial infarct size in swine: a comparative study of intraaortic balloon pumping and transapical left ventricular bypass

This study compared intraaortic balloon pumping (IABP) and transapical left ventricular (LV) bypass for their effectiveness in reducing infarct size in swine. In 28 pigs (25.4 +/- 4.7 kg) the left anterior descending coronary artery was ligated distal to the first diagonal branch. Nine animals served as controls. Nine animals were treated with IABP and the remaining 10, with transapical bypass. Ten animals-3 control, 3 IABP, and 4 transapical bypass--died prior to completion of the study, thereby resulting in 6 animals in each group. Both assist devices were begun 45 minutes after coronary ligation, this being as rapid as mechanical intervention could be accomplished in the patient after infarction. With transapical LV bypass, 70 to 100% bypass was accomplished and the LV systolic pressure remained in the range between mean aortic pressure and 30 mm Hg less than that. All animals were killed after 24 hours. The hearts were excised and stained with nitroblue tetrazolium, and infarct size was quantitated in grams of infarct per 100 gm of LV and septal mass. After 24 hours the mean aortic pressure was 73 +/- 12 mm Hg in controls, 105 +/- 20 mm Hg in animals with IABP (p less than 0.01), and 91 +/- 13 mm Hg in those with transapical LV bypass (p less than 0.05). The infarct size was 22.7 +/- 4.9 gm per 100 gm of LV and septal mass in control animals. With IABP, the infarct size was nonsignificantly changed to 19.4 +/-5.9 gm per 100 gm (p greater than 0.3). With transapical LV bypass, the infarct size was significantly reduced to 15.9 +/- 3.5 gm per 100 gm (p less than 0.025). This represented a 30% reduction of infarct size from controls. These results demonstrate that despite hemodynamic improvement with IABP, transapical LV bypass is necessary to markedly decrease myocardial work and significantly reduce infarct size.