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. 2025 Jan;68(1):125-139.
doi: 10.1007/s10840-024-01873-0. Epub 2024 Aug 21.

Incidence and risk factors for first and recurrent ICD shock therapy in patients with an implantable cardioverter defibrillator

Diana My Frodi  1 , Søren Zöga Diederichsen  1 , Lucas Yixi Xing  1 , Daniel Camillo Spona  1 , Peter Karl Jacobsen  1 , Niels Risum  1 , Jesper Hastrup Svendsen  2   3
Affiliations

Incidence and risk factors for first and recurrent ICD shock therapy in patients with an implantable cardioverter defibrillator

Diana My Frodi et al. J Interv Card Electrophysiol. 2025 Jan.

Abstract

Background: Advances in medical treatment and outcomes in implantable cardioverter-defibrillator (ICD) recipients incentivize a need for improved candidate selection and identification of risk factors for ICD therapy. We examined contemporary rates of and risk factors for ICD therapy.

Methods: Patients with ICD for primary (PP) or secondary prevention (SP), implanted between January 2010 and December 2020, were followed for appropriate and inappropriate incident and recurrent shock.

Results: Overall, 2998 patients (mean age 61.8 ± 12.7 years, 20% female, 73% ICD carriers, and 47.1% SP) were analyzed with a median follow-up of 4.3 (interquartile range (IQR) 2.1-7.4) years. A total of 426/2998 (14.2%) patients had shock; 364/2998 (12.1%) had appropriate and 82/2998 (2.7%) inappropriate shock, with annualized event rates of 2.34 (2.11-2.59) and 0.49 (0.39-0.61) per 100 person-years, respectively. Of those with shock, 133/364 (36.5%) experienced recurrent appropriate shock and 8/364 (2.2%) received recurrent inappropriate shock, with event rates of 10.57 (8.85-12.53) and 0.46 (0.20-0.92), respectively. In multivariable analyses, female sex was associated with a reduced risk of incident appropriate shock (hazard ratio 0.69 [95% confidence interval 0.52; 0.91]). Of other variables, only revascularization status was associated with recurrent appropriate shock in PP, and CRT-D with recurrent appropriate shock in the overall cohort.

Conclusion: One in eight ICD recipients received appropriate shock 2-7 years after guideline-directed implantation. More than one-third of patients with a first shock experienced recurrent shock. Few clinical variables showed potential in predicting shocks, illustrating a need for more advanced tools to select candidates for implantation.

Keywords: ICD-therapy; Implantable cardioverter defibrillator; Recurrent shock; Risk factors; Ventricular arrhythmia.

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Conflict of interest statement

Declarations. Competing interests: Frodi, Xing, Spona, and Risum declare no conflicting interests. Jacobsen has given lectures for Medtronic. Diederichsen is a consultant for Bristol Myers Squibb / Pfizer, Acesion Pharma, Vital Beats and Cortrium. He has received speaker fees from Bristol Myers Squibb / Pfizer and Bayer. Svendsen is a member of an advisory board of Vital Beats and Medtronic and has received speaker’s fee and an unrestricted research grant from Medtronic, independently to this study.

Figures

Fig. 1
Fig. 1
Cumulative incidence of incident ICD shock therapies between PP versus SP Abbreviations: ICD, implantable cardioverter defibrillator; PP, primary prevention; SP, secondary prevention
Fig. 2
Fig. 2
Cumulative incidence of recurrent ICD shock therapies between PP versus SP Abbreviations: ICD, implantable cardioverter defibrillator; PP, primary prevention; SP, secondary prevention
Fig. 3
Fig. 3
Multivariable models on risk factors for ICD therapy This forest plot shows multivariable Cox proportional hazard regression models for time to first of each outcome, for primary and secondary prevention together. Results are given as HR [95% CI], P, and each model was adjusted for covariates as indicated by the given estimates. Abbreviations: BMI, body mass index; BMI category: underweight (BMI < 18.5 kg/m2), overweight (BMI 25–29.9), obese (BMI ≥ 30.0), normal weight (BMI 18.5–24.9); CABG, coronary artery bypass graft; CRT-D, Implantable Cardioverter Defibrillator with cardiac resynchronization therapy; ICD, Implantable Cardioverter Defibrillator; LVEF, left ventricular ejection fraction (Reduced LVEF was defined as LVEF ≤ 35%); PCI, percutaneous coronary intervention
Fig. 4
Fig. 4
Multivariable models on risk factors for ICD therapy following first ICD shock This forest plot shows multivariable Cox proportional hazard regression models for the time from the first to second of each outcome, for primary and secondary prevention together. Results are given as HR [95% CI], P, and each model was adjusted for covariates as indicated by the given estimates. Abbreviations: BMI, body mass index; BMI category: underweight (BMI < 18.5 kg/m2), overweight (BMI 25–29.9), obese (BMI ≥ 30.0), normal weight (BMI 18.5–24.9); CABG, coronary artery bypass graft; CRT-D, Implantable Cardioverter Defibrillator with cardiac resynchronization therapy; ICD, Implantable Cardioverter Defibrillator; LVEF, left ventricular ejection fraction (reduced LVEF was defined as LVEF ≤ 35%); PCI, percutaneous coronary intervention
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