Short-term variability of repolarization predicts ventricular tachycardia and sudden cardiac death in patients with structural heart disease: A comparison with QT variability index

Background: Monitoring arrhythmic risk may improve management of patients with implantable cardioverter-defibrillators (ICD) and prevent ICD shocks. Changes in repolarization duration between subsequent beats quantified as short-term variability (STV) is associated with ventricular arrhythmias in several animal models. Objective: We evaluated STV of QT from right ventricular intracardiac ICD electrograms in patients with structural heart disease and compared its predictive value with the QT variability index (QTVI). Methods: In 233 patients, STV over 60 beats for QT and RR intervals and their ratio was calculated (STV_QT, STV_RR, STV_Ratio, respectively). QTVI was derived from mean and SD of QT and heart rate. Follow-up duration was 26 ± 15 months. Predictive value was determined for sudden arrhythmic death (SAD) defined as sudden cardiac death or fast ventricular tachycardia/fibrillation [CL < 240 ms]. Results: In univariate analysis, STV_Ratio, but not STV_QT or STV_RR, was predictive of SAD. Hazard ratios for highest quartile STV_Ratio and QTVI were comparable (STV_Ratio: 1.9, 95% confidence interval [CI] 1.1 to 3.3, P =.038, QTVI: 2.2, 95% CI 1.2 to 3.8, P =.010). In a multivariate model, highest quartile STV_Ratio was predictive of SAD after adjustment for New York Heart Association class, history of ischemia, ICD indication, and use of class I antiarrhythmics (hazard ratio 1.8, 95% CI 1.0 to 3.4, P <.050). A combined criterion of highest quartile for both STV _Ratio and QTVI identified patients at highest risk (hazard ratio 2.4, 95% CI 1.3 to 4.3, P =.005, positive predictive value 38%, negative predictive value 82%). Conclusion: STV_Ratio from ICD electrograms is predictive of SAD. Predictive value is similar for order-based STV_Ratio and distribution-based QTVI, but the combination of both parameters can further improve results.