President lecture. Observations on myocardial ischemia

Several problems in myocardial ischemia are discussed based on our experimental and clinical studies. Histochemical changes of the myocardium of adult mongrel dogs with a coronary artery ligation were as follows: The most noticeable findings were a decrease of phosphorylase activity in the pericapillary region of the infarcted area and an enlargement of the discoloration area due to fusion according to the prolongation of the ligation period. This may be explained by the fact that ischemic process takes place around the pericapillary zone in the early stage due to an arborescent distribution of the vascular system in the myocardium. This is presumed as one of the factors which induces heterogeneity of the ischemic myocardium. The reversibility of the injured myocardium due to ischemia was investigated electron-microscopically. The time limit of the myocardial reversibility from ischemic damage was 30 to 50 min. Characteristic changes of LDH isoenzymes and the pathohistological changes of the myocardium after ligation and reperfusion of the coronary artery were as follows: a) A decrease of the LD5 (H subunit) fraction degeneration of the myocardial fibers, fibrosis of the connective tissue and scar formation took place. b) The minimum value of LD5 (H subunit) was observed in cases with a 7-day ligation in the ligation group and in cases with a 12-hour ligation which was followed by a 7-day reperfusion in the reperfusion group. c) The time to reach the minimum LD5 value differed between these 2 groups. The most probable cause of this difference is the protection of the myocardium by reperfusion. 4) In 24 dogs 20 mCi 99mTc-PYP was injected intravenously one and a half hours before the reopening of the chest. Then, Tc-PYP images were obtained at frontal and left lateral views. Tc-PYP images of each cross-sectional surface were also obtained. In the ligation group, 99mTc-PYP uptake in the ischemic myocardium was demarcated clearly in cases with a 1-7 day ligation. In the reperfusion group, 99mTc-PYP uptake in the ischemic area was clearly noticed in cases with a 12-hour to 6-day ligation, which was followed by a 1- to 7-day reperfusion. When the period of the reperfusion was prolonged, it became more difficult to obtain a positive image. In 14 patients with acute myocardial infarction Tc-PYP scintigrams were studied with reference to their ECG.(ABSTRACT TRUNCATED AT 400 WORDS)