Prediction of ventricular tachyarrhythmias by intracardiac repolarization variability analysis

Background-Arrhythmic sudden cardiac death (SCD) is generally mediated by ventricular fibrillation (VF) or fast ventricular tachycardia (FVT). We studied the predictive value of temporal QT variability detected from various sources of cardiac electric signal: surface ECG, far-field (FF), and near-field (NF) intracardiac electrograms (EGMs) in patients with implantable cardioverter-defibrillators (ICDs). Methods and Results-Surface ECG and FF and NF intracardiac EGMs were simultaneously recorded at rest (mean heart rate, 74±15 bpm) for 4.5±1.3 minutes in 298 patients (mean age, 59±14; 216 male [73%]) with structural heart disease and an implanted Medtronic ICD for primary (231 patients, 78%) or secondary (67 patients, 22%) prevention of SCD. During mean follow-up of 16±8 months, 52 (13.1% per person-year of follow-up) patients sustained VT/VF and received appropriate ICD therapies, but only 19 (4.8% per person-year of follow-up) patients sustained FVT/VF with cycle length ≤240 ms. The Kaplan-Meier survival analysis showed that the highest QT variability index (QTVI) quartile from all cardiac sources (surface ECG; NF and FF EGMs) is associated with event-free survival (P=0.038 for ECG; P=0.024 for FF EGM; P=0.012 for NF EGM). QTVI was a predictor of all VT/VF events and FVT/VF in the multivariate Cox model (including ischemic or nonischemic cardiomyopathy, history of revascularization procedures, LVEF, New York Heart Association class). Strong significant correlation among QTVI determined from all 3 sources was found. Conclusion-Repolarization lability is present throughout the ventricular myocardium. Increased intracardiac QT variability predicts VT/VF events in patients with structural heart disease.