Survival After Implantable Cardioverter-Defibrillator Shocks

Abstract

Background: There are conflicting data on the impact of implantable cardioverter-defibrillator (ICD) shocks on subsequent mortality.

Objectives: The aim of this study was to determine whether the arrhythmic substrate leading to ICD therapy or the therapy itself increases mortality.

Methods: The study cohort included 5,516 ICD recipients who were enrolled in 5 landmark ICD trials (MADIT-II, MADIT-RISK, MADIT-CRT, MADIT-RIT, RAID). The authors evaluated the association of device therapy with subsequent mortality in 4 separate time-dependent models: model I, type of ICD therapy; model II, type of arrhythmia for which ICD therapy was delivered; model III, combined assessment of all arrhythmia and therapy types during follow-up; and model IV, incremental risk associated with repeated ICD shocks.

Results: When analyzed by the type of ICD therapy (model I), a first appropriate ICD shock was associated with increased risk of subsequent mortality with or without concomitant occurrence of inappropriate shock during follow-up (hazard ratio [HR]: 2.78 and 2.31; p < 0.001 and p = 0.12), whereas inappropriate shock alone was not associated with mortality risk (HR: 1.23; p = 0.42). Similarly, ICD therapy for ventricular tachycardia (VT) ≥200 beats/min or ventricular fibrillation (VF) (model II) was associated with increased risk of death with or without concomitant therapy for VT <200 beats/min (HRs: 2.25 and 2.62; both p < 0.001), whereas appropriate therapy for VT <200 beats/min or inappropriate therapy (regardless of etiology) did not reach statistical significance (all p > 0.10). Combined assessment of all therapy and arrhythmia types during follow-up (model III) showed that appropriate ICD shocks for VF, shocks for fast VT (≥200 beats/min) without prior antitachycardia pacing (ATP), as well as shocks for fast VT delivered after failed ATP, were associated with the highest risk of subsequent death (HR: all >2.8; p < 0.001). Finally, 2 or more ICD appropriate shocks were not associated with incremental risk to the first appropriate ICD shock (model IV).

Conclusion: The combined data from 5 landmark ICD trials suggest that the underlying arrhythmic substrate rather than the ICD therapy is the more important determinant of mortality in ICD recipients.

Keywords: ICD shock; heart failure; inappropriate ICD shock; mortality; ventricular fibrillation; ventricular tachycardia.

Conflict of interest statement

Funding Support and Author Disclosures Each of the MADIT trials was funded by an unrestricted research grant from Boston Scientific to the University of Rochester Medical Center, Rochester, New York. The RAID trial was funded by the National Institutes of Health (grant U01HL096607). Dr. Aktaş has received research grants from Boston Scientific and Medtronic. Dr. Zarebas has received research grants from Boston Scientific. Dr. Kutyifa has received research grants from Boston Scientific, Biotronik, ZOLL, and Spire; and has consultant agreements with Zoll and Biotronik. Dr. Daubert has received honoraria for events committee, data safety monitoring board, consulting, advisory boards and lectures from Abbott, Biosense, Biotronik, Boston Scientific, Farapulse, Medtronic, Microport, Phillips, Vytronus, and Zoll; and has received research grants from Abbott and Medtronic. Dr. Estes has served as a consultant for Boston Scientific (education), Medtronic (independent quality physician panel), and Abbott (education). Dr. Goldenberg has received research grants from Boston Scientific, Zoll, Medtronic, Biosense-Webster, and Biotronik.

Copyright © 2021 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

Figures

FIGURE 1. The Risk of Death Following Defibrillator Therapy

Simon-Makuch estimates of the mean cumulative death rate following (A) appropriate ICD shock, (B) appropriate antitachycardia pacing, (C) inappropriate ICD shock, and (D) inappropriate antitachycardia pacing. App = appropriate; ATP = antitachycardia pacing; ICD = implantable cardioverter-defibrillator; Inapp = inappropriate; Td = time-dependent.

FIGURE 2. The Risk of Death Following Sustained Arrhythmia

Simon-Makuch estimates of the mean cumulative death rate following (A) appropriate ICD therapy ventricular tachyarrhythmia ≥200 beats/min, (B) appropriate ICD therapy for ventricular tachyarrhythmia <200 beats/min, (C) inappropriate ICD therapy for atrial arrhythmia, and (D) inappropriate ICD therapy for other reasons. AA = atrial arrhythmia; VF = ventricular fibrillation; VT = ventricular tachycardia; other abbreviations as in Figure 1.

CENTRAL ILLUSTRATION. Combined Assessment of Therapy and Arrhythmia Type on Subsequent Mortality

Forest plot illustrating the estimated hazard ratios (HRs) and 95% confidence intervals (CIs) for each therapy and arrhythmia type on subsequent mortality. Findings are derived from a time-dependent multivariate model that includes all therapies that occurred during follow-up. ATP = antitachycardia pacing; VT = ventricular tachycardia.