Adaptation to the stress of tachycardia in patients with coronary artery disease: insight into the mechanism of the warm-up phenomenon.

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Abstract
Adaptation to exercise or the "warm up phenomenon" has been observed in some patients with angina pectoris. To investigate adaptation, eleven patients with exertional angina pectoris and angiographic evidence of coronary artery disease underwent two identical bouts of sequential tachycardia stress separated by a brief recovery period. Manifestations of ischemia were less during the second stress, as evidenced by a reduction in the severity of angina pectoris, less ST segment depression, and improved lactate extraction. Peak coronary blood flow during the second stress (81 +/- 20 ml/min) was not significantly different from that during the first (95 +/- 32 ml/min). Regional myocardial oxygen consumption, however, was significantly (p = .03) lower during the second stress (8.8 +/- 2.4 ml O2/min) when compared with the first (11.4 +/- 3.0 ml O2/min). Thus, patients with coronary artery disease can develop anginal tolerance to the stress of tachycardia similar to that observed after repeated bouts of exercise. A relative reduction in myocardial oxygen consumption, rather than an increase in coronary blood flow, appears to account for this phenomenon.