PATHOPHYSIOLOGIC FACTORS GOVERNING THE VARIABILITY OF ISCHEMIC RESPONSES TO TREADMILL AND BICYCLE EXERCISE

Ischemic responses may vary considerably when patients with coronary a rtery disease (CAD) are tested serially, but the pathophysiologic mech anisms that govern this variability have not been well evaluated. We t hus evaluated whether clinical, hemodynamic, physiologic, and anatomic factors influenced the variability in ischemic responses among 140 pa tients (mean age 54 +/- 11 years) subjected to both bicycle and treadm ill exercise electrocardiography Radionuclide ventriculography was obt ained 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 hi gher 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 p ain (12% vs 41%, p < 0.001) in the 34 patients with CAD who had ST-seg ment 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 onl y. This variability was strongly related to the functional and anatomi c magnitude of disease. Ischemic variability decreased progressively a s the response of left ventricular ejection fraction (LVEF) to exercis e 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 t hose with an LVEF fall of greater than or equal to 5% with exercise. S imilarly, 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 differe nt 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 f unctional and anatomic magnitude of ischemic heart disease. Variabilit y in ischemic responses is reduced in the presence of multivessel coro nary disease and in patients with abnormal LVEF responses to exercise.