MYOCARDIAL METABOLIC CHANGES DURING REPERFUSION OF VENTRICULAR-FIBRILLATION - A P-31 NUCLEAR-MAGNETIC-RESONANCE STUDY IN SWINE

Objective: Myocardial metabolic requirements during reperfusion of ventricular fibrillation are poorly understood. The objective of this study was to determine if controlled reperfusion after a clinically relevant global ischemia period of 10 mins was sufficient to prevent or reverse myocardial ischemia as indicated by changes in myocardial high energy phosphates, myocardial intracellular pH, and great cardiac vein lactate. Design: Prospective laboratory study with controlled reperfusion. Setting: Research laboratory at a university medical center. Subjects: Five swine weighing 19 +/- 3 kg. Interventions: Ten minutes of nonperfused ventricular fibrillation followed by reperfusion with cardiopulmonary bypass (flow 30 mL/kg/ min) for 50 mins. Measurements and Main Results: Myocardial adenosine triphosphate (ATP), phosphocreatine, and intracellular pH were determined using in vivo P-31 nuclear magnetic resonance. Myocardial blood flow, measured by 15-mu radiolabeled microspheres, was significantly increased above baseline during reperfusion. Phosphocreatine was depleted during the 10 mins of nonperfused ventricular fibrillation, but recovered to 122 +/- 18% of baseline with reperfusion and was 112 +/- 18% at 60 mins (p < .005). ATP concentrations decreased to 51 +/- 16% of baseline after 10 mins of nonperfused ventricular fibrillation, improved to 67 +/- 9% of baseline with early reperfusion, and were 65 +/- 9% of baseline at 60 mins (p < .02). Myocardial intracellular pH improved from 6.11 +/- 0.18 after 10 mins of nonperfused ventricular fibrillation, to 6.89 +/- 0.20 with early reperfusion, and then decreased to 6.85 +/- 0.35 at 60 mins ventricular fibrillation (p <.001). Despite myocardial blood flows higher than baseline during the reperfusion period, great cardiac vein/aortic lactate gradient increased over the reperfusion period. Conclusion: Prolonged reperfusion with supranormal myocardial blood flow does not restore normal myocardial aerobic metabolism in the fibrillating myocardium after a 10-min nonperfused ventricular fibrillation period.