Impaired chronotropic response to exercise stress testing as a predictor of mortality

Context Chronotropic incompetence, an attenuated heart rate response to exe rcise, is a predictor of all-cause mortality in healthy populations. This a ssociation may be independent of exercise-induced myocardial perfusion defe cts, Objective To examine the prognostic significance of chronotropic incompeten ce in a low-risk cohort of patients referred for treadmill stress testing w ith thallium imaging. Design Prospective cohort study conducted between September 1990 and Decemb er 1993, Setting Tertiary care academic medical center, Patients Consecutive patients (1877 men and 1076 women; mean age, 58 years) who were not taking beta-blockers and who were referred for symptom-limite d treadmill thallium testing. Main Outcome Measures Association of chronotropic incompetence, defined as either failure to achieve 85% of the age-predicted maximum heart rate or a low chronotropic index, a heart rate response measure that accounts for eff ects of age, resting heart rate, and physical fitness, with all-cause morta lity during 2 years of follow-up. Results Three hundred sixteen patients (11%) failed to reach 85% of the age -adjusted maximum heart rate, 762 (26%) had a low chronotropic index, and 6 72 (21%) had thallium perfusion defects. Ninety-one patients died during th e follow-up period, After adjustment for age, sex, thallium perfusion defec ts, and other confounders, failure to reach 85% of the age-predicted maximu m heart rate was associated with increased risk of death (adjusted relative risk [RR], 1.84; 95% confidence interval [CI], 1.13-3.00; P=.01), as was a low chronotropic index (adjusted RR, 2.19; 95% CI, 1.43-3.44; P<.001). Conclusion Among patients with known or suspected coronary disease, chronot ropic incompetence is independently predictive of all-cause mortality, even after considering thallium perfusion defects, Incorporation of chronotropi c response into the routine interpretation of stress thallium studies may i mprove the prognostic power of this test.