Usefulness of Q-wave response to exercise as a predictor of coronary artery disease.

In lead CM5, the Q-wave response to exercise has been reported as an effective index in predicting coronary artery disease (CAD) and CAD with left anterior descending (LAD) disease. The purpose of this study was to verify these findings when the Q wave was analyzed in lead CC5 in 135 patients. The sensitivity for abnormal ST depression was 77%, specificity 83% and predictive value 78%. The corresponding values for the abnormal Q-wave response (reduction or no change in Q-wave amplitude) were 70%, 61% and 59%. These differences (except sensitivity) were significant. When either a positive ST or Q-wave response was used, sensitivity, specificity and predictive value did not significantly increase compared with the ST segment alone. In addition, only 45% of normal subjects with false-positive ST depression had a normal Q-wave response (increase) and 57% of patients with false-negative ST responses had an abnormal Q-wave response. When a positive response for CAD with an LAD lesion and for multivessel CAD with LAD narrowing was defined as having a Q-wave reduction, the sensitivities were extremely low (15% and 17%), but both the specificities and the predictive values were 100%. Therefore, the Q-wave analysis in lead CC5 is no more sensitive for detecting CAD than the ST-segment response. However, when a decreased Q-wave amplitude is observed, multivessel CAD and LAD narrowing can be predicted.