Subcutaneous implantable cardioverter-defibrillators: long-term results of the EFFORTLESS study

Abstract

Aims: To report 5-year outcomes of EFFORTLESS registry patients with early generation subcutaneous implantable cardioverter-defibrillator (S-ICD) devices.

Methods and results: Kaplan-Meier, trend and multivariable analyses were performed for mortality and late (years 2-5) complications, appropriate shock (AS) and inappropriate shock (IAS) rates. Nine hundred and eighty-four of 994 enrolled patients with diverse diagnoses (28% female, 48 ± 17 years, body mass index 27 ± 6 kg/m2, ejection fraction 43 ± 18%) underwent S-ICD implantation. Median follow-up was 5.1 years (interquartile range 4.7-5.5 years). All-cause mortality was 9.3% (95% confidence interval 7.2-11.3%) at 5 years; 703 patients remained in follow-up on study completion, 171 withdrew including 87 (8.8%) with device explanted, and 65 (6.6%) lost to follow-up. Of the explants, only 20 (2.0%) patients needed a transvenous device for pacing indications. First and final shock efficacy for discrete ventricular arrhythmias was consistent at 90% and 98%, respectively, with storm episode final shock efficacy at 95.2%. Time to therapy remained unaltered. Overall 1- and 5-year complication rates were 8.9% and 15.2%, respectively. Early complications did not predict later complications. There were no structural lead failures. Inappropriate shock rates at 1 and 5 years were 8.7% and 16.9%, respectively. Self-terminating inappropriately sensed episodes predicted late IAS. Predictors of late AS included self-terminating appropriately sensed episodes and earlier AS.

Conclusion: In this diverse S-ICD registry population, spontaneous shock efficacy was consistently high over 5 years. Very few patients underwent S-ICD replacement with a transvenous device for pacing indications. Treated and self-terminating arrhythmic episodes predict future shock events, which should encourage more personalized device optimization.

Keywords: Implantable cardioverter-defibrillator; Primary prevention; Secondary prevention; Subcutaneous ICD; Sudden death.

Structured Graphical Abstract

Shock efficacy of appropriate episodes experienced by patients in the EFFORTLESS study. Top left: Torso model of the implant location of the Subcutaneous Implantable Defibrillator (S-ICD) Image provided courtesy of Boston Scientific. © 2022 Boston Scientific Corporation or its affiliates. All rights reserved. Top right: Example S-ICD electrogram recording of a shock (lightning bolt icon) delivered to convert a ventricular arrhythmia. (A) Discrete episodes. (B) Storm episodes.

Figure 1

Patient flow chart for the EFFORTLESS subcutaneous implantable cardioverter-defibrillator registry.

Figure 2

(A) Kaplan–Meier complication-free rates for overall complications (types I–III) and for complications caused by the subcutaneous implantable cardioverter-defibrillator system (type I). (B) Kaplan–Meier complication-free rates in years 2–5 comparing patients who did and did not experience a complication in year 1.

Figure 3

(A) Pie chart of patients’ experience with inappropriate episodes; number of patients and percent of patients provided. (B) Kaplan–Meier inappropriate shock-free rates for all inappropriate shock, for inappropriate shock due to cardiac oversensing, and for inappropriate shock due to cardiac oversensing of T-waves.

Figure 4

Kaplan–Meier event-free rates in in years 2–5, comparing patients who did and did not experience an event in year 1. (A) Inappropriate shocks. (B) Appropriate shocks. AS, appropriate shock; IAS, inappropriate shock.

Figure 5

Significant multivariable predictors to the risk of receiving appropriate therapy using Anderson–Gill models. Separate models were constructed and are shown for any type of appropriate therapy (A), received and for receiving appropriate therapy for polymorphic ventricular tachycardia/ventricular fibrillation arrhythmias (B), and monomorphic ventricular tachycardia arrhythmias (C). Predictors modelled as continuous variables are indicated with an ‘asterisk’. ARVC, arrhythmogenic right ventricular cardiomyopathy; CHF, congestive heart failure; CI, confidence interval; DCM, dilated cardiomyopathy; HCM, hypertrophic cardiomyopathy; LVEF, left ventricular ejection fraction; NICM, non-ischaemic cardiomyopathy; NYHA, New York Heart Association.

Figure 6

Shock efficacy of appropriate episodes experienced by patients in the EFFORTLESS study. (A) Discrete episodes. The left-sided histogram provides first- and final shock efficacy over the course of the study for all rhythms and for episodes with monomorphic ventricular tachycardia or polymorphic ventricular tachycardia/ventricular fibrillation rhythms. The right-sided histogram provides first- and final shock efficacy for episodes experienced for each post-implant year. The number of episodes, number of patients, mean number of shocks delivered, and maximum number of shocks delivered are listed below each rhythm type (left histogram) and follow-up year (right histogram). Regression analyses show that neither duration of follow-up (P = 0.60) nor rhythm type (P = 0.28) significantly impacted first shock efficacy nor final shock efficacy (P = 0.62 and P = 0.82, respectively) for discrete episodes. (B) Storm episodes. The left-sided histogram provides efficacy over the course of the study for all storm episodes. The right-sided histogram provides shock efficacy for storm episodes experienced for each post-implant year. The numbers of patients and storm episodes are provided for each data column. Regression analysis showed that that neither duration of follow-up (P = 0.86) nor rhythm type (P = 0.93) significantly impacted shock efficacy for storm episodes. MVT, monomorphic ventricular tachycardia; PVT, polymorphic ventricular tachycardia; VF, ventricular fibrillation; Yr, year.

Figure 7

(A) Kaplan–Meir rate of survival for the EFFORTLESS study, 5-year follow-up, for all patients (n = 984) and for primary prevention, left ventricular ejection fraction (LVEF) ≤ 35% (n = 303). (B) Multivariable predictors of mortality. Predictors modelled as continuous variables are indicated with an ‘asterisk’. COPD, chronic obstructive pulmonary disease; LVEF, left ventricular ejection fraction; TV-ICD, transvenous implantable cardioverter-defibrillator.