Abstract

Impaired heart rate response to exercise is associated with adverse clinical outcomes in healthy adults and those with established coronary artery disease. It is unclear whether this association persists in subjects who have undergone coronary artery bypass grafting (CABG). In this study, 920 subjects enrolled in the Post CABG trial who had undergone CABG with patent saphenous vein grafts at baseline and known to have discontinued beta blockers before exercise were studied. A maximal symptom-limited exercise treadmill test was performed on study entry. Chronotropic variables were measured at peak exercise. Participants were followed for a composite end point of death, myocardial infarction, stroke, or revascularization. Quantitative coronary angiography was performed at follow-up and compared with baseline angiography, with prespecified angiographic end points of the substantial progression of graft disease and complete occlusion. In multivariate analysis, a low chronotropic index was strongly associated with an increased risk for the composite clinical end point (p for trend = 0.04) and angiographic complete occlusion (p for trend = 0.007) but only weakly associated with angiographic substantial progression (p for trend = 0.07). In conclusion, impaired chronotropic response to exercise identifies subjects at risk for clinical outcomes and graft occlusion, even after revascularization with CABG.