Energetic state of the postischemic myocardium and its relation to contractile failure

We used the isolated working rabbit heart preparation as a model to study the relationship between postischemic myocardial dysfunction and the energetic state of the heart in terms of mitochondrial function and myocardial high energy phosphate (HEP) contents. Normothermic global myocardial ischemia (10, 20 and 30 min) was induced. Cardiac function, mitochondrial function and myocardial HEP contents were measured. Viability of the postischemic myocardium was assessed by electron microscopy. Myocardial tissue was found to be intact up to 20 min of ischemia plus reperfusion. Areas of irreversibly damaged myocardium were found after 30 min of ischemia. Myocardial contractile function was significantly depressed after 10 and 20 min of ischemia and severely depressed after 30 min of ischemia. Postischemic myocardial dysfunction was associated with normal mitochondrial function and HEP content after 10 min of ischemia, with near-normal mitochondrial function and HEP content after 20 min of ischemia and with pathologic values after 30 min of ischemia. It is concluded that postischemic myocardial stunning is not associated with a disturbance of the energy producing processes. More severe ischemia however leads to progressive deterioration of mitochondrial function which may contribute to complete deterioration of myocardial contractile function upon reperfusion.