Chronotropic response to exercise - Improved performance of ST-segment depression criteria after adjustment for heart rate reserve

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 mu V identified CAD with a sensitivity of 52%, an ST/HR index of >1.69 mu V/bpm identified CAD with a sensitivity of 90%, and an ST/HR slope of >2.96 mu V/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 far 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.