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

Cardiopulmonary bypass (CPB) causes a well described systemic inflamma tory response. To avoid these potential detrimental effects, coronary artery bypass grafting (CABG) has been attempted off CPB on the beatin g heart. With the use of a left ventricular (LV) assist device during CABG, the heart can be made flaccid with beta-blockade, and the system ic circulation can continue to be supported. The hemodynamic and hemat ologic consequences of left heart bypass with a miniature axial flow p ump were studied in a sheep CABG model. The pump weighs 45 g and was c onnected to standard venous and arterial cannulas. Left sided inflow a nd brachiocephalic outflow were employed. A pump speed of 14,000 rpm r esulted in a flow of 5.63 +/- 0.18 L/min and provided 75% of the LV ou tput 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 pr essure and LV end systolic pressure resulted in a 66% reduction in LV external work under baseline conditions and an 83% reduction in the be ta-blocked ventricle. Myocardial oxygen demand was reduced 16% after a xial flow unloading in the esmolol depressed condition. Right ventricu lar pressures, pulmonary artery flow, LV filling, and oxygenation were adequate in the esmolol depressed animal and remained unchanged throu ghout the experiment. No changes in hematocrit, total bilirubin, lacta te dehydrogenase, or plasma free hemoglobin were detected after 2 hr o f assist. Axial flow left heart bypass results in acceptable hemodynam ics with no hemolysis and may provide an alternative to CPB during CAB G.