A lesson from the controversy about heart rate adjustment of ST segment depression

Computer applications in the interpretation of the exercise electrocardiogram

The exercise electrocardiogram remains the noninvasive diagnostic test of first choice in patients with coronary artery disease. While new technology offers novel diagnostic possibilities and the ability to assess patients unsuitable for exercise testing, no other investigation has to this point furnished the quality of functional information and value-for-predictive accuracy of exercise electrocardiography. In this article, we describe how this central position in the work up of the cardiac patient has been secured through the evolution of the microprocessor. Particularly important has been its ability to harness and present large volumes of raw data, to derive and manipulate multivariate equations for diagnostic prediction, and to run 'expert' systems which can pool demographic and exercise test data, calculate risk scores, and prompt the nonexpert with advice on current management. These key features explain the pivotal role of the exercise test in the diagnostic, and increasingly prognostic, armoury of the cardiovascular clinician.

Accuracy of heart rate-adjusted ST segments in populations with and without posttest referral bias

We compared the accuracy of the ST segment/heart rate (STHR) index and slope to standard criteria (> or =1 mm horizontal/downsloping ST-segment depression at J + 60 msec) in 1358 patients (152 underwent angiography). All exercise tests used the Cornell protocol and computer measurements of maximum ST-segment depression at J + 60 msec. Test accuracy was determined for the entire group with a probability-based method. Thresholds with equal specificity to standard criteria were determined. By using only patients who underwent angiography, neither STHR index nor slope was more accurate than standard criteria (maximum sensitivity: standard criteria, 42%; STHR index, 51%; STHR slope, 40%). However, by using the entire group, both STHR index and slope were more accurate than standard criteria, but only STHR index achieved statistical significance (maximum sensitivity: standard criteria, 31%; STHR index, 60%; STHR slope, 47%). We conclude that heart rate-adjusted ST-segment criteria are more accurate than standard ST-segment criteria. A lack of demonstration of improved accuracy of STHR index and slope only occurs in patients affected by posttest referral bias.

Comparison of the diagnostic accuracy of different methods of measurement of heart rate-adjusted ST-segment depression during exercise testing for identification of coronary artery disease

Within a population of 160 consecutive symptomatic patients who all had undergone catheterization (80 with > or = 1 stenosis > or = 50%), we compared the accuracy of different computerized measurements of the exercise-induced changes in ST-segment: (1) the standard criterion (> or = 0.1 mV flat/downsloping ST depression or > or = 0.15 mV upsloping depression, both 60 ms after the J point); (2) heart rate (HR)-adjusted ST-segment depression (ST/HR index measured at 0, 20, 40, 60, and 80 ms from the J point); (3) the HR-adjusted ST integral (ST/HR integral measured from 0 to 40 ms and from 40 to 80 ms after the J point). None of the ST/HR indexes or integrals were found to have a significantly greater sensitivity than the standard criterion. On the contrary, all ST/HR indexes and integrals showed a higher specificity (0.78 to 0.89) than did the standard criterion (0.65); moreover, the earlier the measurement within the repolarization phase, the better the overall accuracy: 0.71 for the standard criterion, 0.83 (p < 0.001), 0.80 (p < 0.01), 0.78 (p < 0.02), 0.78 (p < 0.02), 0.74 (p = NS) for the ST/HR indexes at 0, 20, 40, 60, and 80 ms, respectively; 0.81 (p < 0.001) and 0.78 (p < 0.02) for the ST/HR integrals calculated from 0 to 40 and from 40 to 80 ms, respectively. Consistently, the receiver-operating characteristic curve areas of ST/HR at 0, 20, and 40 ms were greater than those of ST/HR at both 60 and 80 ms. These findings are divergent from some other results given in published reports. We conclude that the accuracy of all exercise criteria is influenced by the population analyzed: our patients were representative of those currently seen by clinicians.

Heart rate adjustment of ST segment depression and performance of the exercise electrocardiogram: a critical evaluation

Analysis of the rate-related change in exercise-induced ST segment depression using the exercise ST segment/heart rate slope and ST segment/heart rate index can improve the accuracy of the exercise electrocardiogram (ECG) for the identification of patients with coronary artery disease, recognition of patients with anatomically or functionally severe coronary obstruction and detection of patients at increased risk for future coronary events. These methods provide a more physiologic approach to analysis of the ST segment response to exercise by adjusting the apparent severity of ischemia for the corresponding increase in myocardial oxygen demand, which in turn can be linearly related to increasing heart rate. Solid-angle theory provides a model for the linear relation of ST segment depression to heart rate during exercise and a framework for understanding the relation of the ST segment/heart rate slope to the presence and extent of coronary artery disease. False positive and false negative test results of the heart rate-adjusted methods are well known in selected populations and require further clarification. Application of these methods is also highly dependent on the type of exercise protocol, number of ECG leads examined, timing of ST segment measurement relative to the J point and accuracy and precision of ST segment measurement. These methodologic details have been an important limitation to test application when traditional protocols and measurement procedures are required. When applied with attention to required details, the heart rate-adjusted methods can improve the usefulness of the exercise ECG in a range of clinically relevant populations.

Duration and magnitude of ST-segment depression during exercise and recovery: a symmetric relation

The pattern of appearance and disappearance of ST depression on 12-lead electrocardiographic exercise testing in subjects with coronary artery disease (> or = 70% stenosis) and its relation to the severity of disease were prospectively explored in 34 consecutive patients. The first lead to show positivity during exercise also developed maximum ST depression in 73% of patients and was the last lead to lose positivity in recovery (94%). The last lead to show positivity during exercise was first to lose positivity in recovery (92%). Greater ST depression was associated with a greater number of positive leads (p < 0.001; r = 0.7). The duration of ST depression during exercise, maximum ST depression, and recovery time were related (p = 0.001, r = 0.6; p = 0.006, r = 0.5; p < 0.001, r = 0.6, respectively, for the three interactions). However, the correlations of ST depression and recovery time with the severity of vessel disease and with rate-pressure product at initial ST depression were poor, suggesting that the degree of ST-segment depression and recovery time may depend more on the duration and intensity of myocardial ischemia solicited with exercise rather than on the ischemic threshold or on the severity of coronary artery disease.

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 (> or = 0.1 mV horizontal/downsloping ST depression 80 ms after the J point) in 121 patients who had undergone angiography (49 with > or = 1 lesion with > or = 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.

Population selection and performance of the exercise ECG for the identification of coronary artery disease

To quantify the effect of population selection on the performance of exercise ECG criteria for the detection of coronary artery disease, the exercise ECGs of 212 clinically normal nonvolunteer subjects, 31 patients with no significant coronary disease at angiography, 153 patients with clinically stable angina, and 184 patients with catheterization-proved coronary disease were examined. Test specificity was examined separately in clinically normal subjects and in patients with angiographically normal coronary arteries, and test sensitivity was determined separately in patients with stable angina and those with catheterization-proved disease. Definition and selection of normal and abnormal study populations had marked effects on test performance. Standard ECG criteria, a simple ST depression magnitude partition of 150 microV, an ST segment/heart rate (ST/HR) index partition of 1.60 microV/beat/min, and an ST/HR slope partition of 2.40 microV/beat/min, identified coronary disease with comparably high specificities (94% to 97%) in clinically normal subjects, but with significantly lower specificities (68% to 77%, p = 0.002 to 0.0001) in patients with angiographically normal coronary arteries. Although sensitivity was significantly lower in patients with stable angina than in patients with catheterization-proved coronary disease for standard criteria (54% vs 70%, p = 0.004) and for the ST/HR index (88% vs 95%, p = 0.04), there was no significant difference in the poor sensitivity of the simple ST depression magnitude criteria (51% vs 58%) or in the high sensitivity of the ST/HR slope (93% vs 96%) in these abnormal patient groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic accuracy of seismocardiography compared with electrocardiography for the anatomic and physiologic diagnosis of coronary artery disease during exercise testing

A multicenter study was performed to compare the diagnostic accuracy of a new technique, seismocardiography, with that of electrocardiography for physiologically and anatomically significant ischemic coronary artery disease (CAD) during exercise stress testing. Five participating centers enrolled 129 patients who had simultaneous seismocardiograms and 12-lead electrocardiograms at the time of their exercise treadmill stress tests. Two different definitions of CAD were used: anatomic and physiologically significant disease. The presence of anatomically significant CAD (> or = 50% diameter stenosis) was documented by coronary angiography. Physiologically significant CAD was defined as present in the same 129 patients when coronary arteriography (> or = 50% diameter stenosis) and thallium-201 scintigraphy (defect on initial postexercise images) were both abnormal. Seismocardiography had a significantly better sensitivity for detecting anatomic CAD than did electrocardiography (73 vs 48%; p < 0.001), without loss of specificity (78 vs 80%; p = NS). Exercise seismocardiography added significant incremental diagnostic information beyond that provided by exercise electrocardiography. Seismocardiography was more sensitive (without less specificity) in women and in patients who did not achieve maximal predicted heart rate. In patients with physiologically significant CAD, the seismocardiogram was also significantly more sensitive (78%) than was the electrocardiogram (55%) (p < 0.02), without loss of specificity (84 vs 74%). Seismocardiography significantly improved sensitivity for the detection of anatomic and physiologic CAD. It is easy to perform and may be a clinically useful adjunct in exercise stress testing.

Accuracy of ST/heart rate index in the diagnosis of coronary artery disease

The accuracy of ST/heart rate (ST HR) index was evaluated in patients presenting for exercise electrocardiography with suspected coronary disease. In all, 420 patients (235 men and 185 women) with normal electrocardiograms at rest underwent exercise testing, followed within 3 months by coronary angiography. The sensitivity and specificity for standard ST criteria (greater than or equal to 1 mm horizontal or downsloping depression) were 48% (78 of 162) and 81% (208 of 258), respectively. An ST HR-index threshold of 1.86 microV/beta/min had the exact same specificity with a sensitivity of 44% (71 of 162; p = not significant). Consideration of greater than or equal to 1.5 mm upsloping depression had no significant impact on the aforementioned results. Using multivariate logistic regression analysis, age, sex, symptoms, cigarette smoking, diabetes mellitus, qualitative ST slope, rate-pressure product, METs achieved and exercise angina were evaluated with and without ST HR index and ST depression. According to this analysis, age, sex, symptoms and ST slope were good predictors of presence or absence of disease. Neither ST HR index nor ST depression had significance in the multivariate analysis. However, when a separate analysis was performed in men and women, the 2 quantitative ST variables showed significance in men, but not in women. Comparisons of discriminative accuracy using receiver-operating characteristic curves demonstrated differences between men and women, but no difference between ST HR index and ST depression. Therefore, concerning questions of coronary disease diagnosis, consideration of ST HR index was not better than standard ST criteria, and added nothing to multivariate analysis of other available variables.