Usefulness of impaired chronotropic response to exercise as a predictor ofmortality, independent of the severity of coronary artery disease

Chronotropic incompetence, or on attenuated heart rate response to exercise , has been shown to be associated with an adverse outcome. it is not known whether chronotropic incompetence predicts all-cause mortality independent of angiographic severity of coronary artery disease (CAD). Study subjects i ncluded consecutive patients who underwent first-time, symptom-limited exer cise treadmill testing and coronary angiography within 90 days; no patient was taking beta blockers or had a history of heart failure, valve disease, or prior revascularization. Chronotropic response was measured in 2 ways: ( 1) failure to reach 85% of the age-predicted maximum heart rate, and (2) a low chronotropic index, a measure of exercise heart rate response that acco unts for effects of age, physical fitness, and resting heart rate. Angiogra phic severity of CAD wets assessed using the Duke Prognostic Weight Score, with a score greater than or equal to 42 considered to be indicative of sev ere CAD. Among 384 eligible patients, failure to reach 85% of the age-predi cted maximum heart rate occurred in 61 (16%) and a low chronotropic index w as noted in 133 (35%). Severe CAD was present in 63 (16%). During 6 years o f follow-up there were 56 deaths. Mortality was predicted by failure to rea ch target heart rate (RR 1.85, 95% confidence interval [CI] 1.01 to 3.39, c hi-square = 4, p = 0.05), by severe CAD (RR 2.21, 95% CI 1.24 to 3.95, chi- square = 8, p = 0.007), and, most strongly, by a low chronotropic index (RR 2.72, 95% CI 1.60 to 4.61, chi-square = 15, p = 0.0002). In a multivariabl e model, low chronotropic index remained predictive of death (adjusted RR 2 .22, 95% CI 1.29 to 3.82, p = 0.004), whereas severe CAD no longer predicte d death (adjusted RR 1.27, 95% CI 0.70 to 2.31, p > 0.4). Thus, chronotropi c incompetence is a strong and independent predictor of death, even after a ccounting for the angiographic severity of CAD. (C) 2000 by Excerpta Medica , Inc.