EFFECT OF BETA-BLOCKADE ON THE INTERPRETATION OF THE EXERCISE ECG - ST LEVEL VERSUS DELTA-ST/HR INDEX

The diagnostic value of exercise-induced ST segment depression is considered to be decreased in patients receiving beta-blockers. One approach to improving predictive accuracy has been to use the ratio of maximal change in exercise-induced ST segment depression to the corresponding maximal change in heart rate (DELTA ST/HR index). The present study compared these two ECG methods. The records of exercise tests performed on 3047 male veterans were screened to exclude patients with prior revascularization procedures or myocardial infarction, those receiving digoxin, and those with certain resting ECG abnormalities; the use of beta-blocker drugs at the time of testing was also noted. All exercise tests were sign/symptom limited. Significant angiographic coronary disease was defined as greater-than-or-equal-to 75% reduction in luminal diameter of at least one coronary artery. Disease severity was evaluated in an expanded study group that included patients with prior myocardial infarction. Mean maximal heart rate was 21 beats . min-1 lower for those receiving beta-blockers (p < 0.05), but there was no difference in mean metabolic equivalent (MET) level achieved. The diagnostic accuracy of an abnormal test result for determination of the presence or absence of coronary artery disease was not significantly different in the subgroup taking beta-blockers versus the subgroup not taking beta-blockers (N = 200), and use of the DELTA ST/HR index did not improve test performance. For discrimination of severe disease, test accuracy was also unaffected by beta-blockers and was not improved by the DELTA ST/HR index (N = 454). Exercise testing is a useful predictor of the presence and/or severity of coronary artery disease in patients taking beta-blockers. Withholding these medications before testing does not appear to alter interpretation of the exercise ECG.