MECHANICAL UNLOADING WITH A MINIATURE AXIAL FLOW PUMP AS AN ALTERNATIVE TO CARDIOPULMONARY BYPASS

Abstract

Cardiopulmonary bypass (CPB) causes a well described systemic inflammatory response. To avoid these potential detrimental effects, coronary artery bypass grafting (CABG) has been attempted off CPB on the beating heart. With the use of a left ventricular (LV) assist device during CABG, the heart can be made flaccid with beta-blockade, and the systemic circulation can continue to be supported. The hemodynamic and hematologic consequences of left heart bypass with a miniature axial flow pump were studied in a sheep CABG model. The pump weighs 45 g and was connected to standard venous and arterial cannulas. Left sided inflow and brachiocephalic outflow were employed. A pump speed of 14,000 rpm resulted in a flow of 5.63 +/- 0.18 L/min and provided 75% of the LV output during a 2 hr pump run. This resulted in complete capture of the aortic pressure tracing (mean 56.3 mmHg) with a 15.5 mmHg augmentation in the esmolol depressed ventricle. Reductions in LV end diastolic pressure and LV end systolic pressure resulted in a 66% reduction in LV external work under baseline conditions and an 83% reduction in the beta-blocked ventricle. Myocardial oxygen demand was reduced 16% after axial flow unloading in the esmolol depressed condition. Right ventricular pressures, pulmonary artery flow, LV filling, and oxygenation were adequate in the esmolol depressed animal and remained unchanged throughout the experiment. No changes in hematocrit, total bilirubin, lactate dehydrogenase, or plasma free hemoglobin were detected after 2 hr of assist. Axial flow left heart bypass results in acceptable hemodynamics with no hemolysis and may provide an alternative to CPB during CABG.