Effect of ST segment measurement point on performance of standard and heart rate-adjusted ST segment criteria for the identification of coronary artery disease.

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Abstract
BACKGROUND Recent reports critical of the performance of heart rate-adjusted indexes of ST depression during exercise electrocardiography have used J-point rather than ST segment measurements. However, no standard exists for the optimal time after the J-point at which to measure ST segment deviation. METHODS AND RESULTS To assess the effect of ST segment measurement position on performance of standard exercise electrocardiographic criteria, the delta ST segment/heart rate (delta ST/HR) index, and the ST segment/heart rate (ST/HR) slope for the detection of coronary artery disease, the exercise electrocardiograms of 50 clinically normal subjects and 80 patients with known or likely coronary disease were analyzed using ST depression measured at both the J-point and at 60 msec after the J-point (J + 60). A positive exercise electrocardiogram by standard criteria, defined as 0.1 mV or more of additional horizontal or downsloping ST depression at end exercise, had a specificity of 96% when ST depression was measured at either the J-point or J + 60. There was no difference in sensitivity of standard electrocardiographic criteria at J + 60 and J point (both 59%, p = NS). However, at matched specificity of 96%, the delta ST/HR index and ST/HR slope calculated using ST depression at J + 60 were significantly more sensitive (90% and 93%) than when calculated using J-point depression (64% and 61%, each p less than 0.001). Comparison of areas under respective receiver operating characteristic curves confirmed the superior performance of J + 60 as opposed to J-point measurements for both the delta ST/HR index (0.98 versus 0.89, p = 0.006) and the ST/HR slope (0.96 versus 0.87, p = 0.007) and also demonstrated modestly improved overall test performance for standard electrocardiographic criteria using J + 60 measurements (0.88 versus 0.82, p = 0.001). CONCLUSIONS Use of J-point measurements significantly degrades performance of heart rate-adjusted indexes of ST depression but has less effect on standard criteria.