Exercise QT Dispersion as an Independent Predictor of the Presence of Ischemia on Myocardial Perfusion Imaging

Background: Increased QT dispersion on resting electrocardiography has been shown to be related to ischemia and to predict adverse cardiac events. The purpose of the present study was to evaluate the relationship between myocardial ischemia and the exercise QT dispersion response. Methods: We studied 368 patients with normal resting electrocardiograms referred for exercise SPECT myocardial perfusion scintigraphy because of suspected coronary disease. We used signal‐averaged recordings of 12‐lead electrocardiograms to manually measure QT dispersion at rest and peak exercise. We interpreted scintigrams visually as ischemic or nonischemic. Results: The 49 patients with scintigraphic ischemia were compared to the 319 patients without ischemia. Resting QT dispersion did not differ, but exercise QT dispersion was significantly greater in those with ischemia (25 ± 13 ms vs 32 ± 15 ms; P = 0.0004). Using logistic regression analysis with any ischemia present or absent as the dependent variable, exercise QT dispersion was an independent predictor (P = 0.0006) of the presence of ischemia. We also found a significant increase in receiver operating characteristic curve area when exercise QT dispersion was included in the model (areas 0.74 ± 0.04 vs 0.78 ± 0.03; P = 0.035). Exercise QT dispersion as a dependent variable was independently associated with sex (increased in women) and perfusion ischemia (positive relation). Conclusion: Exercise QT dispersion is an independent predictor of the presence of scintigraphic ischemia that has incremental value over other clinical and exercise test variables.