Objectives: The aim of this study was to test the hypothesis that the warm-up phenomenon is attributable to a reduction of increased myocardial oxygen consumption rather than to increased coronary blood flow during exercise.
Background: The underlying mechanism of the warm-up phenomenon is not elucidated.
Methods: Thirteen patients with effort angina were subjected to two consecutive supine ergometer exercise tests performed 15 min apart. All patients had severe proximal stenosis (> 90%) in the left anterior descending coronary artery. Great cardiac vein flow was measured before and during exercise. Both regional myocardial oxygen consumption and adenosine release were determined.
Results: Exercise was continued for significantly longer before angina onset in the second than in the first exercise test (507 +/- 44 vs. 410 +/- 42 s, p < 0.01). The extent of ST segment depression in lead V5 of the electrocardiogram (ECG) was larger at the time of angina onset in the first (1.7 +/- 0.2 mm) than in the second (1.1 +/- 0.2 mm, p < 0.01) exercise test. Neither systemic hemodynamic variables nor great cardiac vein flow differed between the first and second exercise tests. In contrast, regional myocardial oxygen consumption assessed at 3 min of exercise was significantly (p < 0.01) less in the second than in the first test (8.0 +/- 0.8 vs. 8.7 +/- 0.9 ml/min). Adenosine release during the second test was higher (p < 0.05) than in the first test (2.5 +/- 0.5 vs. 3.9 +/- 0.5 nmol/min at 3 min of the first and second tests, p < 0.01).
Conclusions: These results indicate that the warm-up phenomenon is not attributable to increased coronary flow but to attenuation of increased regional myocardial oxygen consumption, which may be mediated by adenosine A1 receptor activation.