CORONARY RESERVE AND EXERCISE ECG IN PATIENTS WITH CHEST PAIN AND NORMAL CORONARY ANGIOGRAMS

Background. Coronary vasodilator reserve is reduced in some patients with a history of chest pain and angiographically normal coronary arteries. ECG changes suggestive of myocardial ischemia during exercise also can be demonstrated in a subset of these patients. Methods and Results. We have investigated the correlation between coronary vasodilator reserve, assessed with N-13-labeled ammonia and positron emission tomography, and the ECG during exercise stress in 45 patients with a history of chest pain, angiographically normal coronary arteries, and a negative ergonovine test. ST segment depression on the ECG during exercise was present in 29 of 45 patients. Mean resting left ventricular blood flow was 1.04+/-0.22 ml . min-1 . g-1; it increased to 1.32+/-0.47 ml . min-1 . g-1 (p<0.01 versus baseline value) during atrial pacing and to 2.52+/-0.96 ml . min-1 . g-1 (p<0.01 versus baseline value) after dipyridamole (0.56 mg/kg i.v.). No regional flow defects could be demonstrated in any patient during pacing or after dipyridamole. Myocardial flows after dipyridamole, however, did not show a normal frequency distribution (Kolmogorov-Smirnov test), and two patient populations could be identified. Twenty-nine (67%) patients had a mean left ventricular flow of 3.02+/-0.33 ml . min-1 . g-1 after dipyridamole (range, 2.13-5.46 ml . min-1 . g-1), and 14 (33%) patients had a mean flow of 1.48+/-0.29 ml . min-1 . g-1 (range, 1.06-2.04 ml . min-1 . g-1, p<0.01 versus the "high-flow group"). Conclusions. Approximately one third of patients in our series showed a reduced coronary vasodilator reserve. Although 12 of 14 patients in the "low-flow group" had ST segment depression during exercise stress, 16 of 29 patients in the high-flow group also had ST segment depression during exercise stress. Therefore, despite a good sensitivity (86%) in identifying patients with a blunted increment of coronary flow, the ECG response during exercise stress appears to have a rather low specificity (45%). This suggests that factors other than reduced coronary reserve and myocardial ischemia may play a role in the genesis of the ST segment depression in these patients.