What Induces the Warm-Up Ischemia/Angina Phenomenon: Exercise or Myocardial Ischemia?

Abstract

Background— The relation of the warm-up ischemia phenomenon to the presence and intensity of initial myocardial ischemia is unclear. We sought to determine whether the warm-up ischemia phenomenon requires initial myocardial ischemia or can be induced by exercise without ischemia and whether there is a relation between the intensity of initial ischemia and the attenuation of ischemia on reexercise. Methods and Results— Twelve subjects with exertional myocardial ischemia performed 2 exercise ECG tests (1 and 2) at a ±10-minute interval on 3 occasions (A, B, C) 1 month apart. A1 and A2 were symptom-limited. B1 was kept as long as A1, but its intensity was held under the ischemic threshold (heart rate×systolic pressure at 1-mm ST depression [STD]) noted at A1. B2 was symptom-limited. C1 was also kept as long as A1 but with an intensity adjusted to maintain one-half maximum STD of A1. C2 was symptom-limited. Exercise duration of A2, B2, and C2 increased similarly compared with A1 ( P =0.009). However, the ischemic threshold (×10 −3 ) increased at A2 (23.5±6.0) compared with A1 (20.3±4.8; P <0.0001) but not at B2 (19.8±5.0) or C2 (21.5±5.8). Similarly, maximum STD adjusted to the highest heart rate–systolic pressure product common to A1, A2, B2, and C2 decreased at A2 (1.4±0.7 mm) compared with A1 (2.5±0.9 mm; P <0.0001) but not at B2 (2.7±0.9 mm) or C2 (2.3±0.9 mm). Conclusions— Exercises under the ischemic threshold and of intermediate ischemic intensity increase short-term exercise capacity, but myocardial ischemia of more than moderate intensity is needed to induce the warm-up ischemia phenomenon.