Shintaro Koyama

Depression of the S-T segment in epicardial electrocardiogram associated with experimental major coronary artery constriction.

Summary Electrocardiograms in more than 15 leads were recorded from the left ventricular surface during graded constriction of the major coronary arteries or their branches in anesthetized dogs. With mild to moderate constriction of the left circumflex, the anterior descending artery or their distal branches, a horizontal or flat depression of the S-T segment was recorded from leads over the distribution area of each constricted artery. The depth of S-T depression was of greatest magnitude at the border and decreased as the center was approached. S-T elevation or decreasing magnitude of S-T depression began to develop following severe constriction. These results will provide an experimental basis for interpretation of electrocardiographic changes during angina pectoris. In contrast to the border of the ischemic area, where S-T depression was recorded with any degree of constriction, elevation after severe constriction was not infrequently the only S-T displacement at the center. It is suggested that the direction of S-T displacement following coronary artery constriction depends on the position of the electrode with respect to the ischemic area. The epicardial S-T depression observed in this study is thought to be a reciprocal effect of subendocardial injury, as has been generally accepted.

ST-segment fluctuation during treadmill exercise in patients with angina pectoris.

The level of the ST-segment fluctuates transiently during treadmill exercise in some patients with angina pectoris. In the present study, the incidence and clinical significance of ST-segment fluctuation were studied before and after propranolol in 52 patients with angina pectoris. A transient greater than 0.5-mm (0.05 mV) upward shift of the ST-segment during a graded treadmill test was considered a significant fluctuation in leads without signs of previous myocardial infarction. The fluctuation was observed in three of 30 patients with rest or rest and effort angina pectoris before propranolol and in 14 of them after propranolol, while only one of 22 patients with effort angina alone showed fluctuation after the drug. Coronary arteriography revealed that in 15 patients showing ST-segment fluctuation with propranolol, seven patients had no significant coronary stenosis, six had one-vessel disease and two had two-vessel disease. In 24 patients with documented coronary artery spasm, ST-segment fluctuation was induced in two (8%) before propranolol and in 13 (54%) after propranolol. Our results suggest that ST-segment fluctuation during graded treadmill exercise may be related to transient coronary vasospasms exacerbated by propranolol.