Diagnostic accuracy of heart rate-adjusted ST segments compared with standard ST-segment criteria

We compared the accuracy of ST segment/heart rate (ST/HR) index with that of standard criteria (≥0.1 mV horizontal/downsloping ST depression 80 ms after the J point) in 121 patients who had undergone angiography (49 with ≥1 lesion with ≥50% stenosis) and 50 clinically normal subjects. All exercise tests used the Cornell protocol and computer measurements of maximal ST depression 80 ms after the J point. Thresholds with equal specificity to standard criteria were determined for ST/HR index using each of the 2 normal groups (those who were normal by angiography and those who were clinically normal). In using only patients who underwent angiography, we found that the ST/HR index had a sensitivity that was not significantly greater than that of standard criteria (standard criteria 51%, ST/HR index 59%; p = 0.21). However, the receiver-operating characteristic curve area increased from 64 ± 4 to 68 ± 4 (p < 0.02). When clinically normal subjects were used instead of patients without angiographic disease, there was a clearly discernible improvement in sensitivity of ST/HR index over standard criteria (standard criteria 51%, ST/HR index 69%; p < 0.05). The associated curve areas were 69 ± 4 and 79 ± 3 (p < 0.001). Therefore, accuracy of the ST/HR index was marginally better than standard criteria only in patients who underwent angiography. When clinically normal subjects were used, the accuracy of the ST/HR index was definitely better than standard criteria. We conclude that the demonstration of improved accuracy of the ST/HR index depends on the population being tested.