The purpose of this study was (1) to monitor myocardial high-energy phosphate content and recovery of left ventricular (LV) contractile function following normothermic graded cardiac ischemia and single-dose hypothermic potassium cardioplegia, and (2) to assess the temporal limits of LV functional recovery during single-dose cardioplegia maintained at 17°C. Rabbit hearts (30) were perfused, equipped with an LV balloon, paced at 240 beats/min, and placed in a nuclear magnetic resonance (NMR) magnet. Hearts underwent either graded, global normothermic ischemia or potassium cardioplegia arrest maintained at 17°C for 1 hr. Myocardial high-energy phosphate level, LV contractility, and temperature were monitored continuously. Phosphocreatine (PCr) fell to 10 ± 2, 2 ± 1, and 0% of control and ATP to 70 ± 3, 19 ± 7, and 0% of control at 10, 40, and 60 min of 37°C ischemia. After 1 hr of reperfusion, regression analysis of final developed pressure (DP) on end ischemic ATP (EIATP) content revealed: DP = 1.02 EIATP + 18 (r = 0.95). Following single-dose cardioplegia, maintained at 17°C, PCr fell to 16 ± 3% of control at 60 min while ATP fell only to 92 ± 5% control. With reperfusion, recovery of DP was 100%. It was concluded that (1) PCr serves as an energy buffer for ATP, (2) EIATP predicts recovery of LV function, (3) single-dose cardioplegia maintained at 17°C provides complete myocardial preservation for up to 60 min.
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