MYOCARDIAL HYPOXIA AND ANAEROBIC METABOLISM IN CORONARY HEART DISEASE

Oxygen needs of the heart were abruptly increased by electrically induced elevation in heart rate. The presence of myocardial tissue hypoxia was judged by an increase in the lactate pyruvate concentration ratio in the coronary venous blood ( L Pcv), and myocardial anaerobic metabolism was detected by lactate output into the coronary venous blood [negative coronary (a-v) L]. Elevation in heart rate did not result in signs of myocardial hypoxia or anaerobic metabolism in any of 6 normal subjects. In 8 of 12 patients with coronary heart disease, elevation in heart rate resulted in an increase in L Pcv. In 4 of these 8, the O2 concentration in the coronary venous blood remained constant or rose, data consistent with augmented coronary blood flow but myocardial hypoxia due to abnormal distribution of the blood through the myocardium. In 4 patients there was a fall in coronary venous blood O2 concentration as well as in increase in L Pcv, evidence of myocardial hypoxia due to a failure to increase total coronary blood flow. Anaerobic metabolism by the myocardium developed in 3 patients. Nine patients with coronary heart disease experienced angina pectoris after several minutes of elevated heart rate. In 2 patients angina spontaneously disappeared coincident with a return of the increased L Pcv toward normal, despite the fact that heart rate was maintained at the elevated level. These results suggest delayed improvement in distribution of blood flow as an explanation for the phenomenon of second wind" in angina pectoris. © 1968."