Effect of baseline ST segment elevation on test performance of standard and heart rate-adjusted ST segment depression criteria.

Whether the ST segment shift used to evaluate the presence and severity of myocardial ischemia should include the additional deviation due to decreasing amounts of baseline ST segment elevation was examined in 100 clinically normal subjects and in 124 patients with coronary disease. Exercise ST segment depression was calculated in two ways: as the difference between exercise and resting ST segment depression, but excluding any resting ST elevation (STdep), and as the total ST segment difference or excursion, including any baseline resting ST elevation (STdiff). These values were also used for separate calculation of the maximal ST/heart rate slope and delta ST/heart rate index in each case. Given partition values with matched specificity of 95% in clinically normal subjects, 150 microV of STdep was significantly more sensitive for coronary disease than 220 microV of STdiff (61% [76 of 124] versus 50% [62 of 124], p less than 0.005). Comparison of receiver operating characteristic curves confirmed the superior test performance of STdep for the identification of coronary disease in this population (area under the curve 0.920 versus 0.869, p = 0.0019). In contrast, detection of three-vessel coronary obstruction by standard ST segment criteria was not affected by definition of ST segment excursion. Substitution of STdiff for STdep did not change the performance of the ST/heart rate slope of the delta ST/heart rate index for either the detection of coronary disease or for the identification of three-vessel coronary obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)