Strong coherence between heart rate variability and intracardiac repolarization lability during biventricular pacing is associated with reverse electrical remodeling of the native conduction and improved outcome

Background: Reverse electrical remodeling (RER) of the native conduction with cardiac resynchronization therapy (CRT) is associated with decreased mortality and antiarrhythmic effect of CRT. Still, mechanisms of RER are largely unknown. In this study, we explored repolarization lability during biventricular pacing. Methods and Results: The width of native QRS was measured in lead II electrocardiogram before and at least 6 months after implantation of Cardiac Resynchronization Therapy Defibrillator (CRT-D) devices (Medtronic, Inc [Minneapolis, MN, USA] and Boston Scientific Corporate [Natick, MA, USA]) in 69 patients (mean age, 66.3 ± 13.9 years; 39 men [83%]) with either bundle-branch block (44 patients [64%]) or nonspecific intraventricular conduction delay (25 patients [36%]) and New York Heart Association class III and IV heart failure. Narrowing of the native QRS duration for at least 10 milliseconds was considered a marker of RER. Beat-to-beat QT variability and coherence was measured on surface electrocardiogram and intracardiac near-field electrogram during biventricular pacing. Reverse electrical remodeling was observed in 22 patients (32%) in whom coherence between heart rate variability and intracardiac repolarization lability was stronger (0.483 ± 0.243 vs 0.237 ± 0.146, P =.018) and normalized intracardiac QT variance was smaller (0.28 ± 0.0031 vs 0.46 ± 0.0048, P =.049), as compared with that in patients without RER. During a further 24 ± 13 months of follow-up, 21 patients (33%) died or experienced sustained ventricular tachycardia (VT)/ventricular fibrillation. Low intracardiac coherence (≤0.116) was associated with increased risk of death or sustained VT/VT (hazard ratio, 4.33; 95% confidence interval, 1.51-12.40; P =.006). Conclusion: Strong coherence between heart rate variability and intracardiac repolarization lability during biventricular pacing is associated with RER of the native conduction with CRT. Low coherence is associated with increased risk of VT/ventricular fibrillation or death.