Tissue and coronary venous pH in ischemic canine myocardium

The relationship between changes in myocardial tissue pH and local coronary venous pH during and after transient occlusion of the left anterior descending artery was investigated in 6 open chested anesthesized dogs. Tissue pH was recorded with a needle pH electrode, and coronary venous pH with a specially designed catheter tip pH electrode. Myocardial tissue pH fell steadily after coronary occlusion, and had fallen by 0.107 +/- 0.043 pH units (mean +/- SD, n = 12, occlusions) after 150 s. On reperfusion there was a further small fall in tissue pH to 0.138 +/- 0.035 units before tissue pH returned to control. In contrast, the fall of coronary venous pH during ischemia was small (0.15 +/- 0.027 after 150 s, n = 12 occlusions). Within 5 s of reperfusion, a large fall in venous pH occurred, reaching a maximum of 0.150 +/- 0.072 at 20-30 s after reperfusion. During ischemia changes in tissue pH are poorly represented by changes in coronary venous pH. The size of early change of venous pH during the reperfusion washout of retained metabolites is a better estimate of the fall of tissue pH. Measurement of metabolites in the coronary sinus of man during the washout after the end of an ischemic intervention such as a trial pacing is superior to measurements performed during pacing in providing biochemical evidence of myocardial ischemia.