Pathophysiologic factors governing the variability of ischemic responses to treadmill and bicycle exercise

Ischemic responses may vary considerably when patients with coronary artery disease (CAD) are tested serially, but the pathophysiologic mechanisms that govern this variability have not been well evaluated. We thus evaluated whether clinical, hemodynamic, physiologic, and anatomic factors influenced the variability in ischemic responses among 140 patients (mean age 54 ± 11 years) subjected to both bicycle and treadmill exercise electrocardiography. Radionuclide ventriculography was obtained during bicycle exercise in each patient. The population included 77 patients with CAD, 21 patients with normal coronary arteriograms, and 42 patients with <5% likelihood of CAD. Bicycle exercise evoked higher systolic blood pressure (p < 0.001) and double-product (p < 0.001) responses compared with treadmill exercise in the patients with CAD and in the normal subjects, and it evoked a lower frequency of chest pain (12% vs 41%, p < 0.001) in the 34 patients with CAD who had ST-segment depression during both exercise tests. There was a high frequency of variability in ischemic responses during treadmill versus bicycle exercise: 22 (39%) of the 56 CAD patients who had exercise-induced ST-segment depression manifested this response during one stress test only. This variability was strongly related to the functional and anatomic magnitude of disease. Ischemic variability decreased progressively as the response of left ventricular ejection fraction (LVEF) to exercise worsened progressively (p = 0.003 by analysis of variance), from 83% in those with an LVEF increase of >10% with exercise to only 13% in those with an LVEF fall of ≥5% with exercise. Similarly, ischemic variability occurred in 8 (89%) of 9 patients with single-vessel CAD versus 14 (30%) of 47 patients with multivessel CAD (p < 0.005). In conclusion, bicycle and treadmill exercise are different stressors, evoking different hemodynamic and clinical responses in patients with CAD. Ischemic ECG responses vary considerably when these patients undergo both stresses. This variability is governed by the functional and anatomic magnitude of ischemic heart disease. Variability in ischemic responses is reduced in the presence of multivessel coronary disease and in patients with abnormal LVEF responses to exercise.