Long-Term Survival and Predictive Relevance of Nocturnal Ventricular Tachyarrhythmias Requiring Appropriate Implantable Cardioverter-Defibrillator Therapy

Background: Whether nocturnal ventricular tachyarrhythmias (VTAs) are associated with poorer long-term survival than daytime VTAs remains unclear. This study aimed to investigate the association between nocturnal VTAs and long-term survival, as well as the associated prognostic relevance. Methods: Implantable cardioverter-defibrillator (ICD) recipients from the Study of Home Monitoring System Safety and Efficacy in Cardiac Implantable Electronic Device-implanted Patients (SUMMIT) registry were retrospectively analyzed using data from home monitoring transmissions. Nocturnal VTAs were defined as episodes occurring between 22:00 and 05:59, whereas daytime VTAs were defined as those occurring during the remaining 16 hours (06:00–21:59). Results: Over a median follow-up of 61.7 months, 102 cardiac deaths and 187 deaths from any cause were recorded. Among 730 patients, 422 experienced VTAs, of whom 231 (54.7%) had nocturnal VTAs. Compared with patients without VTAs, those with nocturnal VTAs had a 62% higher risk of cardiac death (hazard ratio (HR), 1.62; 95% confidence interval (CI): 1.02–2.59; p = 0.041) and a 2.3-fold higher risk of all-cause mortality (HR, 2.30; 95% CI: 1.50–3.53; p < 0.001). Patients with nocturnal VTAs experienced more ICD shocks (77.9% [180/231] vs. 59.2% [113/191]; p < 0.001), more electrical storms (46.8% [108/231] vs. 9.4% [18/191]; p < 0.001), and a higher VTA burden (median, 1.36 [IQR, 3.44] vs. 0.59 [IQR, 1.01] episodes per year) than those with daytime-only VTAs. Elevated nighttime heart rate and reduced left ventricular ejection fraction (LVEF), as well as male sex and prior atrial fibrillation, were identified as independent risk factors for nocturnal VTAs. Conclusions: Nocturnal VTAs were not uncommon. Patients experiencing nocturnal VTAs had a higher risk of cardiac death and all-cause mortality. Monitoring the occurrence and timing of VTA episodes may be a useful tool for identifying high-risk patients. Clinical Trial Registration: ChiCTR-ONRC-13003695, https://www.chictr.org.cn/showproj.html?proj=5865.