Effects of chronotropic incompetence and β-blocker use on the exercise treadmill test in men

Objective Our purpose was to assess the diagnostic characteristics of the exercise test in patients who fail to reach conventional target heart rates and in patients on β-blockers. Background Exercise test results are often considered “inadequate” or “nondiagnostic” in patients taking β-blockers and in patients who do not achieve 85% of their age-predicted maximal heart rate. Methods The results of exercise tests and coronary angiography performed to evaluate chest pain in 1282 male patients without a prior history of myocardial infarction, coronary revascularization, diagnostic Q wave on the baseline electrocardiogram, or previous cardiac catheterization were analyzed with respect to β-blocker exposure and failure to reach 85% age-predicted maximal heart rate. Sensitivity, specificity, and predictive accuracy of exercise testing, as well as area under the curve for the receiver operating characteristic plots were calculated for these subgroups with use of coronary angiography as the reference. The angiographic criterion for significant coronary artery disease was 50% narrowing or greater in one or more major coronary arteries. Results The population was divided into 4 exclusive groups on the basis of whether they reached their target heart rates and whether they were receiving β-blockers. Sixty to 40 percent of this clinical population failed to reach target heart rate, of which 24% (n = 303) were receiving β-blockers and 40% (n = 518) were not. The group of patients who reached target heart rate and were not taking β-blockers was taken as the reference group (n = 409). The group of patients supposedly β-blocked but who reached the target heart rate (n = 52) had hemodynamic and test characteristics similar to those of the reference group and most likely were not taking their β-blockers or were not adequately dosed. The prevalence of angiographic coronary disease was significantly higher in the 2 groups failing to reach target heart rate, both in the presence and absence of β-blockers, compared with the reference group (68% and 64%, respectively, vs 49%, P <.01). Although the areas under the curve of the receiver operating characteristic curves for ST depression of the groups failing to reach target heart rate were not significantly different from the reference group, the predictive accuracy and sensitivity were significantly lower for 1 mm of ST depression in the β-blocked group who did not reach target heart rate (predictive accuracy of 56% vs 67%, sensitivity of 44% vs 58%, P <.01). The only way to maintain sensitivity with the standard exercise test in the β-blocker group who failed to reach target heart rate was to use a treadmill score or 0.5-mm ST depression as the criteria for abnormal. Conclusion Sensitivity and predictive accuracy of standard ST criteria for exercise-induced ST depression are significantly decreased in male patients who are taking β-blockers and do not reach target heart rate. In those who fail to reach target heart rate and are not β-blocked, sensitivity and predictive accuracy are maintained. (Am Heart J 2001;142:136-41.)