Flow requirements in ventricular fibrillation: An in vivo nuclear magneticresonance analysis of the left ventricular high-energy phosphate pool

Study objective: We sought to determine whether flow rates of approximately 60% of normal Values are sufficient to preserve the left ventricular myoca rdial high-energy phosphate pool during ventricular fibrillation (VF). Methods: Mixed-breed swine (weight 22.4+/-2.5 kg) were anesthetized with al pha-chloralose, placed in a slate of VF, and perfused with extracorporeal c irculation at a target flow of 50 mL.kg(-1).min(-1). In vivo whole-wall (av erage of left ventricular wall) and spatially localized phosphorous-31 nucl ear magnetic resonance (NMR) spectra were acquired at baseline and during V F. Results: Mean flow during VF was 58+/-20 mL.kg(-1).min(-1) (+/-SD; 95% conf idence interval, 44 to 71) or about 60% of baseline cardiac output (n=13). Whole-wall adenosine triphosphate (ATP) decreased during perfused VF (P<.05 ), whereas creatine phosphate (CP) remained unchanged from baseline. With s patially localized NMR, the ratios of CP/ATP were similar at baseline in al l layers (endocardium --> epicardium) of the left ventricular wall. However , during perfused VF, subepicardial CP/ATP ratios increased by 14% to 40% c ompared with baseline values, whereas subendocardial CP/ATP ratios remained unchanged (1% to 3% increase). An additional 4 animals perfused at 72+/-10 mL.kg(-1).min(-1) (+/-SD; 95% confidence interval, 56 to 92) during VF had preservation of CP and ATP levels. Conclusion: Flow levels equivalent to 60% of baseline cardiac output were i nsufficient to maintain normal high-energy phosphate levels in the in vivo fibrillating myocardium. At this level of flow, myocardial high-energy phos phate loss is nonhomogeneous within the left ventricular wall.