Chronotropic Response to Exercise

Abstract

Background Heart rate (HR) response to exercise plays an important role in the diagnosis of coronary artery disease (CAD). Adjustment of ST-segment depression for the change in HR with exercise increases the accuracy of the exercise ECG in the detection of CAD. In addition, an attenuated HR response to exercise, a manifestation of chronotropic incompetence, may have independent diagnostic value for CAD. Methods and Results The diagnostic value of adjusting the magnitude of ST-segment depression, the ST-segment (ST)/HR index, and the ST/HR slope for chronotropic response to exercise was assessed in 283 control subjects and 337 patients with CAD by dividing each ST measurement by the fraction of HR reserve achieved. At a matched specificity of 96%, ST-segment depression of >160 μV identified CAD with a sensitivity of 52%, an ST/HR index of >1.69 μV/bpm identified CAD with a sensitivity of 90%, and an ST/HR slope of >2.96 μV/bpm identified CAD with a sensitivity of 88%. Adjustment for HR reserve improved the sensitivity of each method: adjusted ST-segment depression of >176 had a sensitivity of 87% ( P <.0001), an adjusted ST/HR index of >2.14 had a sensitivity of 94% ( P =.005), and an adjusted ST/HR slope of >3.47 had a sensitivity of 93% ( P =.0001). In addition, the 94% and 93% sensitivities of the adjusted ST/HR index and ST/HR slope were significantly greater than the 87% sensitivity of adjusted ST-segment depression ( P <.0001). Conclusions Correction for an attenuated HR response to exercise improves performance of the simple and HR-adjusted ST-segment depression criteria for the identification of CAD. These findings support assessment of the degree of chronotropic reserve in routine evaluation of the exercise ECG.