Comparison of direct mechanical ventricular actuation and cardiopulmonary bypass

Direct mechanical ventricular actuation (DMVA) is a non-blood-contacting method for biventricular support. To compare effects of DMVA and cardiopulmonary bypass (CPB), 13 swine were supported by DMVA or CPB during 4 hours of ventricular fibrillation. Hearts were then rapidly excised and sectioned into right ventricular (RV) and left ventricular (LV) free wall slabs and subjected to total normothermic ischemia. Time to peak ischemic contracture (TIC) of LV endocardium (endo), LV epicardium (epi) and RV were determined using Millar needle transducers. Mean TIC was compared between DMVA (n = 6), CPB (n = 7), and control (n = 18). Significant decreases in LV endo TIC were found after DMVA (53.3 +/- 3.3 min) and CPB (56.2 +/- 2.4 min) compared with control (62.5 +/- 1.0), p less than 0.05. Myocardial blood flow was measured using microspheres during normal sinus rhythm and after 2 and 4 hr of circulatory support. Nonsignificant decreases in endo flow occurred during CPB and DMVA compared with control. LV endo adenosine triphosphate (ATP) levels (mumol/g dry weight) were significantly decreased after DMVA (9.0 +/- 2.5) and CPB (4.0 +/- 2.7) compared with control (17.8 +/- 0.6), p less than 0.05. Although CPB maintained mean arterial pressure by increased pump flows (mean, 129 ml/kg/min) and LV intracavitary pressures were kept below 5 mmHg with LV venting, resulting endo flows and ATP levels were decreased. DMVA generated decreased cardiac outputs (mean, 67 ml/kg/min) under these vasodilated states, yet maintained endo flow and ATP levels as well as CPB. These experimental data show that different mechanisms of myocardial perfusion and metabolism result from CPB and DMVA.