Similar time course of ST depression during and after exercise in patients with coronary artery disease and syndrome X

Abstract

To assess whether the time course of ST segment depression differs in patients with coronary artery disease and patients with angina and normal coronary arteries, the exercise tests of 54 patients with documented coronary artery disease and 25 patients with syndrome X (angina, positive exercise test, no evidence of coronary artery spasm, and normal coronary arteries) were compared. All tests were performed with therapy withheld, using the modified Bruce protocol. In each test, time, heart rate and blood pressure were measured at the onset and at 1 mm of ST segment depression, and at peak exercise. Recovery (return of the ST segment to baseline ±0.2 mm) time was also assessed. Peak ST segment depression was similar in coronary artery disease and syndrome X patients (1.5 ± 0.3 versus 1.6 ± 0.4 mm). In 42 coronary artery disease patients, ST segment depression developed early (≤6 minutes) during exercise; this was associated with a short recovery (≤3 minutes) in 17 (40%) and with a long recovery (>3 minutes) in 25 (60%) patients. In 17 patients with syndrome X, ST segment depression developed early; it was associated with a short recovery in six (35%) and with a long recovery in 11 (65%) patients. Late (>6 minutes) onset of ST segment depression was observed in 12 coronary artery disease patients; of these, eight (67%) had a short recovery and 4 (33%) had a long recovery. Late onset of ST segment depression occurred in eight patients with syndrome X; six (75%) had a short recovery and two (25%) had a long recovery. Average time, heart rate, and heart rate-blood pressure product were higher in syndrome X than in coronary artery disease patients, both at 1 mm of ST segment depression (618 ± 74 versus 468 ± 234 seconds, p < 0.01; 140 ± 19 versus 117 ± 22 beats/min, p < 0.001; and 239 ± 60 versus 193 ± 56 beats/min·mm Hg·10 −2, p < 0.05, respectively) and at peak exercise (708 ± 144 versus 546 ± 246 seconds, p < 0.01; 145 ± 18 versus 124 ± 23 beats/min, p < 0.001; and 256 ± 42 versus 213 ± 61 beats/min·mm Hg·10 −2, p < 0.05, respectively). One millimeter of ST segment depression developed at a heart rate ≤ 110 beats/min in 47% of coronary artery disease patients but in only 4% of syndrome X patients. Thus the time course of ST segment depression during exercise is similar in syndrome X and in coronary artery disease, but the heart rate at which diagnostic ST segment depression develops is significantly different in these two conditions.