QT Dispersion Is Determined by the Extent of Viable Myocardium in Patients With Chronic Q-Wave Myocardial Infarction

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Abstract
Background QT dispersion is lower in patients with successful thrombolysis after acute myocardial infarction, suggesting that QT dispersion may be determined by the extent of viable and scarred myocardium. Methods and Results To test this hypothesis, QT dispersion was measured in a 12-lead resting ECG in 44 patients with chronic Q-wave myocardial infarction. To assess the extent of viable and scarred myocardium, all patients underwent F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET). In addition, all patients had revascularization of the infarct-related artery and repeated angiography 4 months later. QT dispersion was lower (53±20 versus 94±24 ms, P <.0001) in patients with evidence of a substantial amount of viable myocardium in the infarct region as demonstrated by PET (average FDG uptake ≥50% of normalized, maximum FDG uptake) than in patients with only minimal residual viability. Average FDG uptake of the infarct region and FDG defect size were significantly related to QT dispersion ( r =.64, P <.0001; r =.67, P <.0001), whereas ejection fraction was not ( r <.1, P =NS). QT dispersion of ≤70 ms had a sensitivity of 85% and a specificity of 82% to predict viable myocardium in the infarct region. QT dispersion was also lower in patients with improvement of left ventricular function 4 months after revascularization (54±21 versus 88±30 ms, P =.0003). QT dispersion of ≤70 ms had a sensitivity of 83% and a specificity of 71% to predict improvement of left ventricular function. Conclusions QT dispersion is determined by the amount of viable myocardium in the infarct region and may serve as a novel, rapidly available marker of substantial viability in the infarct region of patients with chronic Q-wave myocardial infarction.