Longitudinal changes in intracardiac repolarization lability in patients with implantable cardioverter-defibrillator

Background: While it is known that elevated baseline intracardiac repolarization lability is associated with the risk of fast ventricular tachycardia (FVT)/ventricular fibrillation (VF), the effect of its longitudinal changes on the risk of FVT/VF is unknown. Methods and Results: Near-field (NF) right ventricular (RV) intracardiac electrograms (EGMs) were recorded every 3-6 months at rest in 248 patients with structural heart disease [mean age 61.2 ± 13.3; 185(75%) male; 162(65.3%) ischemic cardiomyopathy] and implanted cardioverter-defibrillator (ICD) or cardiac resynchronization therapy defibrillator (CRT-D) [201 (81%) primary prevention]. Intracardiac beat-to-beat QT variability index (QTVI_NF) was measured on NF RV EGM. During the first study phase (median 18 months), participants made on average 2.4 visits. Then remote follow-up was continued for an additional median period of 3 years. Average QTVI_NF did not change during the first year after ICD implantation (-0.342 ± 0.603 at baseline vs. -0.262 ± 0.552 at 6 months vs. -0.334 ± 0.603 at 12 months); however, it decreased thereafter (-0.510 ± 0.603 at 18 months; P = 0.042). Adjusted population-averaged GEE model showed that the odds of developing FVT/VF increased by 75% for each 1 unit increase in QTVI_NF. (OR 1.75 [95%CI 1.05-2.92]; P = 0.031). However, individual patient-specific QTVI_NF trends (increasing, decreasing, flat) varied from patient to patient. For a given patient, the odds of developing FVT/VF were not associated with increasing or decreasing QTVI_NF over time [OR 1.27; (95%CI 0.05-30.10); P = 0.881]. Conclusion: While on average the odds of FVT/VF increased with an increase in QTVI_NF, patient-specific longitudinal trends in QTVI_NF did not affect the odds of FVT/VF.