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

Objective: Myocardial metabolic requirements during reperfusion of ven tricular fibrillation are poorly understood. The objective of this stu dy was to determine if controlled reperfusion after a clinically relev ant global ischemia period of 10 mins was sufficient to prevent or rev erse myocardial ischemia as indicated by changes in myocardial high en ergy phosphates, myocardial intracellular pH, and great cardiac vein l actate. Design: Prospective laboratory study with controlled reperfusi on. Setting: Research laboratory at a university medical center. Subje cts: Five swine weighing 19 +/- 3 kg. Interventions: Ten minutes of no nperfused ventricular fibrillation followed by reperfusion with cardio pulmonary bypass (flow 30 mL/kg/ min) for 50 mins. Measurements and Ma in Results: Myocardial adenosine triphosphate (ATP), phosphocreatine, and intracellular pH were determined using in vivo P-31 nuclear magnet ic resonance. Myocardial blood flow, measured by 15-mu radiolabeled mi crospheres, was significantly increased above baseline during reperfus ion. Phosphocreatine was depleted during the 10 mins of nonperfused ve ntricular fibrillation, but recovered to 122 +/- 18% of baseline with reperfusion and was 112 +/- 18% at 60 mins (p < .005). ATP concentrati ons decreased to 51 +/- 16% of baseline after 10 mins of nonperfused v entricular fibrillation, improved to 67 +/- 9% of baseline with early reperfusion, and were 65 +/- 9% of baseline at 60 mins (p < .02). Myoc ardial intracellular pH improved from 6.11 +/- 0.18 after 10 mins of n onperfused ventricular fibrillation, to 6.89 +/- 0.20 with early reper fusion, and then decreased to 6.85 +/- 0.35 at 60 mins ventricular fib rillation (p <.001). Despite myocardial blood flows higher than baseli ne during the reperfusion period, great cardiac vein/aortic lactate gr adient increased over the reperfusion period. Conclusion: Prolonged re perfusion with supranormal myocardial blood flow does not restore norm al myocardial aerobic metabolism in the fibrillating myocardium after a 10-min nonperfused ventricular fibrillation period.