Background The dynamic nature of QT dispersion (QTd) and the absence of an acceptable normal value suggest that the relative change not the absolute value of QTd would be a better predicator of coronary restenosis. We sought to examine the usefulness of the relative change in QTd, compared to the absolute value, as a predictor for coronary restenosis after previously successful percutaneous transluminal coronary angioplasty (PTCA).
Methods Ninety-two patients with a history of successful PTCA who were referred for coronary angiography (CA) for exclusion of coronary restenosis were included in this analysis. QTd was calculated as the difference in milliseconds between the maximum and minimum QT interval in the 12-lead ECG. Relative change in QTd was measured as [QTd at the time of angiography (current) - QTd after the successful PTCA (baseline)]/QTd (baseline) %. Receiver operating characteristics (ROC) analysis was used to detect the best cut-off point and also to compare the diagnostic accuracy of the relative change in QTd vs. the absolute QTd for prediction of coronary restenosis.
Results The relative change in QTd showed a significantly larger ROC area under curve (AUC) compared to the absolute QTd [AUC (95% CI): 0.79 (0.698, 0.872) and 0.61 (0.498, 0.703) respectively; p=0.011 for AUCs comparison]. The best cut-off point for the relative QTd was 40%, and for the absolute QTd this was 50 ms. The sensitivity and specificity of ≥40% increase in QTd to detect coronary restenosis was 71% and 83%, with positive and negative predictive values of 90% and 57%, respectively. The diagnostic accuracy of the absolute value of QTd was much less than this; the sensitivity and specificity of QTd ≥50 ms were 48% and 58%, with positive and negative predictive values of 71% and 34%, respectively.
Conclusions Compared to the absolute value, the relative change in QTd is a better predictor of coronary restenosis after a previously successful PTCA. These findings may open the door for rethinking the use of QTd as a simple ECG predictor for cardiovascular outcomes.
2009 by The Japanese Society of Internal Medicine