Simultaneous evaluations of contractility and energy metabolism of stunned myocardium using 31P magnetic resonance spectroscopy

A canine model of postischemic myocardial dysfunction (15min ischemia, 60min reperfusion) was used to evaluate the relationship between energy metabolism and myocardial contractile function by on-line measurements of ECG, left ventricular pressure, coronary blood flow and regional segment shortening (%SS) with the continuous acquisition of 31PMR spectra. Two groups emerged from these studies; the first (n=7) in which regional myocardial %SS remained significantly depressed after 60min of reperfusion (stunned) and the second (n=5) in which regional %SS returned to control levels after 60min of reperfusion (non-stunned). Both groups exhibited rapid, similar decreases in %SS and parallel rapid decreases in the phosphocreatine to inorganic phosphate (PCr/Pi) ratio with the onset of ischemia. The PCr/ATP ratio exceeded control levels in the stunned group immediately upon reperfusion and remained significantly above control after 60min of reperfusion. Measurements of tissue myocardial creatine kinase (CK) revealed a significant decrease in total tissue CK activity in stunned myocardium compared to control. A significant inverse relationship (r=-0.904, p<0.003) was found between myocardial tissue CK specific activity and the PCr/ATP ratios. We postulate that the elevated PCr/ATP ratio caused by the impairment of energy transfer to the contractile apparatus constitutes a contractile dysfunction in the postischemic heart.