Transmural distribution of myocardial high energy phosphates and lactate in relation to the epicardial ECG in the underperfused canine heart.

The influence of coronary perfusion pressure (CPP) on the transmural distribution of myocardial metabolites was examined in the canine heart. Myocardial contents of high energy phosphates and lactate were measured in the inner, middle and outer third of transmural biopsies taken from the underperfused area of the left ventricle; simultaneously epicardial ECG was recorded. Maximum autoregulation of flow was reached when CPP was decreased by approximately 50%; this was indicated by the absence of reactive hyperemia. At this level, high energy phosphate and lactate contents as well as hemodynamic function remained relatively unaltered. At 40% of CPP, coronary flow and the high energy phosphate contents decreased significantly, especially in the subendocardium. At 30% of CPP, there was an accumulation of lactate and a decrease in creatine phosphate content to below one-third of the control in all layers; under these conditions also the ST-segment of the epicardial ECG was elevated. The ST-segment appeared to be relatively insensitive to subendocardial damage; instead, elevation of the ST-segment seemed to be correlated wit the content of lactate in the subepicardium.