The 'warm-up' phenomenon occurs in patients with chronic stable angina but not in patients with syndrome X

Most patients with chronic stable angina show an improvement in ischemic threshold when a second exercise test is performed a few minutes after a first positive test. In this study we evaluated whether this 'warm-up' phenomenon also occurs in patients with syndrome X. We performed 2 consecutive exercise tests in 14 patients with chronic stable angina and 11 patients with syndrome X. The second exercise test was performed after 10 minutes from the end of the first one, always after complete recovery to baseline of ST segment. In patients with stable angina, heart rate (108 ± 18 vs 99 ± 16 beats/min, p = 0.005), rate-pressure product (17,020 ± 4,541 vs 15,215 ± 3,734 beats/min x mm Hg, p = 0.028), and exercise time (587 ± 297 vs 444 ± 244 seconds, p = 0.002) at 1-mm ST depression were higher in the second test than in the first one and a significant improvement in these parameters during the second test was also observed at peak exercise. Conversely, in patients with syndrome X, there were no significant differences between the 2 tests in heart rate (128 ± 18 vs 131 ± 23 beats/min), rate-pressure product (19,922 ±: 5,153 vs 19,390 ± 5,654 beats/min x mm Hg), and exercise time (592 ± 243 vs 566 ± 228 seconds) at 1-mm ST-segment depression. Similarly, in this group of patients, no significant differences in exercise variables between the 2 tests were observed at peak exercise. Thus, unlike patients with chronic stable angina, patients with syndrome X have no evidence of warm-up in response to repeated exercise testing.