Diagnostic Properties of Exercise Electrocardiographic Leads and Variables in the Detection of Coronary Artery Disease

In Finland, coronary artery disease (CAD) is the main cause of death among the middle-aged population. The exercise electrocardiographic (ECG) test is the most widely used non-invasive method of assessing CAD. However, diagnostic performance in conventional analysis of the exercise ECG is limited to approximately 75%; many patients in need of treatment may thus be excluded from subsequent examinations and too many are needlessly referred for further investigation, causing unnecessary anxiety. The objectives of this series of studies were to compare and assess the diagnostic properties of the ECG leads and to evaluate the effect of number and selection of leads on these properties in the detection of CAD, using different ST and ST/HR variables. Studies of the diagnostic properties of the standard 12 ECG leads and comparisons of the ST and ST/HR variables have been made in different clinical populations comprising 409 patients and subjects undergoing the computerized exercise ECG test: 128 patients with significant CAD proved by coronary angiography, 220 patients with a low likelihood of CAD, and 61 asymptomatic volunteer subjects. The principal statistical method adopted in comparing the discriminative capacities of the exercise ECG variables was receiver operating characteristic (ROC) analysis. Comparisons of sensitivity at fixed specificity were made using McNemar's modification of the χ2-test for paired proportions. Marked differences were observed in the diagnostic properties of individual leads. In each variable the highest areas under the ROC curves were in chest leads V5 and V6, and in limb leads I and –aVR. However, the cut-off criterion applied to leads I and aVR should be 50% smaller. The most deficient areas under the ROC curves were distinctly chest lead V1 and limb lead aVL in all variables (p <0.0001 vs. V5 and I in each variable). The areas under the ROC curves for end-exercise ST-segment depression defined as maximum value over the lead set with 5, 9 and 12 leads were 0.894, 0.859 and 0.791, respectively. A statistically significant difference was observed between each lead set. Comparison between the ECG variables showed the superiority of ST/HR hysteresis. In conclusion, the exercise ECG leads have dissimilar diagnostic properties in the detection of CAD and the fixed partition criterion for each lead is inappropriate. The diagnostic properties of ST/HR hysteresis were significantly better than those of the other exercise ECG variables used.