Heart rate adjustment of ST segment depression for improved detection of coronary artery disease.

Abstract

Normal values for heart rate-adjusted indexes of ST segment depression during treadmill exercise electrocardiography (the ST segment/heart rate slope and the AST segment/heart rate index) were derived from evaluation of 150 subjects with a low likelihood of coronary artery disease, including 100 normal subjects and 50 subjects with nonanginal chest pain. Partitions chosen by the method of percentile estimation to include 95% of normal subjects remained highly specific in subjects with nonanginal pain syndromes. Sensitivities of the derived partitions for detection of myocardial ischemia were tested in an additional 150 patients with a high likelihood of coronary disease, including 100 patients with angiographically demonstrated coronary obstruction and 50 patients with stable angina. In contrast to the 68% (102 of 150 subjects) sensitivity of standard exercise electrocardiographic criteria for the detection of disease in this population, the sensitivity of an ST segment/heart rate slope partition of 2.4 liV/ beats/min was 95% (142 of 150 subjects, p < 0.001), and the sensitivity of a AST segment/heart rate index partition of 1.6 ,V/beats/min was 91% (137 of 150 subjects, p <0.001). Analysis of receiver-operating curves confirmed the superior performance of the heart rate-adjusted indexes throughout a wide range of test specificities. These findings suggest that heart rate adjustment of ST segment depression can markedly improve the clinical usefulness of the treadmill exercise electrocardiogram. (Circulation 1989;79:245-255 Therefore, the purpose of this study was to establish normal limits during treadmill exercise for the ST/HR slope and for an extreme simplification of the original method, the AST/HR index.20'2' These findings were then used to test the ability of heart rate adjustment of ST segment depression to improve the electrocardiographic detection of coronary artery disease. Methods Study PopulationThree hundred consecutively studied subjects and patients who met criteria outlined below were by guest on May 9, 2018 http://circ.ahajournals.org/ Downloaded from

Heart rate adjustment of exercise-induced ST segment depression. Improved risk stratification in the Framingham Offspring Study.

“…Because both the AST/HR index and ST/HR slope are continuous variables that reflect this relation in a quantitative fashion, their values can be accurately related to both the presence and severity of CHD. 3,12,13,25,29 In contrast, during early recovery, the magnitude of ST segment depression in patients with CHD generally remains greater than expected for the rapidly decreasing myocardial oxygen demand that results from an abrupt lowering of exercise load, producing a counterclockwise rate-recovery loop pattern.14 Because direction of the rate-recovery loop is not dependent on a particular threshold magnitude of ST segment depression at peak exercise, sensitivity of this method for identifying CHD may be less affected by the anatomic and functional severity of underlying coronary obstruction than are standard and heart rate-adjusted criteria that are derived from exercise-phase data alone.14 Although the AST/HR index significantly concentrates risk in the present study, the more complex ST/HR slope method might have performed with greater accuracy. Although the ST/HR slope relates changing ST depression to heart rate changes occurring during maximum ischemia, the AST/HR index relates overall ST depression to the total heart rate change during exercise.12,'325,29 Because this total change in heart rate may include a variable period of effort during which ischemia is absent, the AST/HR index should not as effectively normalize ST depression for oxygen demand during ischemia as does the maximal ST/HR slope and, therefore, may not as accurately reflect the presence and severity of coronary obstruction.29 Further study is necessary to evaluate the potential of this method to stratify risk of coronary events; this may be facilitated by the recent implementation of accurate, on-line computerized calculation of the ST/HR slope.50…”

Comparison of ST segment/heart rate index to standard ST criteria for analysis of exercise electrocardiogram.

“…We have found that bias resulting from this factor can significantly affect the reputed accuracy of exercise testing. 15 An example of such bias is illustrated in the report of Kligfield et al 5 These investigators excluded equivocals (17% of study group) from the numerators for the calculation of sensitivity and specificity. In an overview of 147 publications, we found this treatment of equivocal results used only one time.22 Such a biased treatment of equivocals falsely improves both sensitivity and specificity.23 The test results so assigned and therefore excluded involved upsloping ST segments.…”

Diagnostic Value of the Recovery Time-Course of ST Slope on Exercise ECG in Discriminating False-From True-Positive ST-Segment Depressions

“…To improve the accuracy of the exercise ECG, various indices have been proposed, including the degree of STsegment depression, 1,16,17 R wave amplitude changes, 18,19 ST/HR slope, 20,21 ST index, 21,22 QT dispersion, 2,23 ST slope 1,7,16,24,25 and concomitant changes in hemodynamic parameters. 1,17 Each has been reported to improve accuracy; however, only a few are in clinical use, presumably because there has not been a dramatic increase in accuracy, the method is complicated or time-consuming, or both.…”