Recovery of left ventricular function after graded cardiac ischemia as predicted by myocardial P-31 nuclear magnetic resonance

The purpose of this study was to determine noninvasively some critical level of high-energy phosphate stores that relates to the recovery of ventricular contractile function after graded cardiac ischemia. Rabbit hearts (n = 30) were equipped with an intraventricular balloon to monitor developed pressure and ± dp/dt and placed in a nuclear magnetic resonance magnet (Bruker, 4.7 Tesla). Each heart underwent 10, 20, 40, or 60 minutes of global ischemia followed by 1 hour of reperfusion. The pH as determinated by nuclear magnetic resonance dropped from 7.14 ± 0.04 to 7.07 ± 0.07 (p<0.02) at 1 minute and to 6.19 ± 0.08 at 30 minutes of ischemia; pH ceased to fall thereafter. Phosphocreatine was depleted to 10% ± 7% of its preischemic control in 10 minutes. Adenosine triphosphate (ATP) concentrations were 71% ± 14% and 1% ± 2% at 10 and 60 minutes. Regression analysis of recovered developed pressure on end-ischemic ATP (EIATP) revealed; developed pressure = 0.93 (EIATP) + 23 (r² = 0.99). We conclude that: (1) anaerobic metabolism as evidenced by a fall in pH appears to be active for 30 minutes after normothermic ischemia and then ceases; (2) phosphocreatine buffers the fall in ATP during early ischemia; (3) there is a tight correlation between EIATP and recovery of left ventricular contractile function with a threshold content of approximately 80% below which recovery of function will not be complete.