Interpreting the exercise electrocardiogram in patients either on β-blocking drugs or with chronotropic incompetence

Abstract

In the current issue of the Journal, Gauri et al address the issue of the diagnostic implications of the failure to achieve 85% of the age-predicted maximum heart rate with and without the influence of β-blocking drugs. They make a number of interesting observations concerning patients who come for diagnostic exercise testing. With use of a receiver operating characteristic (ROC) curve area approach, the authors demonstrated that the exercise ST-segment response did not have incremental value over pretest clinical data in patients receiving βblockers who failed to achieve the target peak heart rate. Because the ROC approach considers all diagnostic thresholds of ST-segment response, it was also important to look at the results using the specific cut point of 1 mm of ST segment depression, which is heavily relied on by practicing physicians. Comparison of sensitivity and predictive accuracy at this cut point confirms that patients on β-blockers have lower accuracy than those not receiving β-blockers. However, they also demonstrated that those patients on β-blocking drugs had a significantly greater prevalence of coronary disease. Although the analysis did not confirm whether this relationship was independent of other predictors, there are at least 2 other previous reports that have made similar observations.1 Review of the database at West Virginia University confirms this observation but also suggests that the presence of β-blockers is not an independent predictor of angiographic coronary disease. However, in an unselected exercise test population, the presence of β-blockers is strongly related to the pretest probability of coronary disease (unpublished observations). This suggests that the presence of β-blockers reflects pretest referral bias so that patients with a greater likelihood of coronary disease are more likely to end up on β-blockers for one reason or another. Of particular interest is the observation by Gauri et al