Long term shock efficacy of the subcutaneous defibrillator in the EFFORTLESS extension sub study

Introduction EFFORTLESS was a post-approval study of the subcutaneous defibrillator (S-ICD) where patients (pts) were implanted with the S-ICD and followed for up to 5 years. The EFFORTLESS Extension was created to follow subgroup of pts, to report on long term S-ICD outcomes. Purpose To assess long-term shock efficacy and time to therapy for pts who experienced appropriate episodes for pts enrolled in the EFFORTLESS extension phase. Hypothesis: Shock efficacy and time to therapy did not differ significantly over time. Methods Appropriate episodes were delineated as discrete or part of a storm event defined as ≥3 episodes in 24 hours. Time to therapy was defined as the interval starting 2000 ms after the last induction artefact and ending at the onset of the shock deflection on a standard ECG recording. Effects of time and rhythm type on first and final shock efficacy were evaluated using logistic regression and effects of time and rhythm type on time to therapy were evaluated using a linear regression preceded by logarithmic transformation. Results Of the 985 pts in the EFFORTLESS main study, 203 were enrolled in the study’s extension study phase. At original study enrollment, pts in this extension cohort were 49±16 years old, 24% were female, and clinical characteristics were: ejection fraction 41±17%, 74% primary prevention indication, 37% previous MI/ischemia/CAD, 29% hypertension, and 8% diabetes (Table). Overall, pts enrolled in the study and extension were followed for 9.3 years (range 4.4-10.8 years). During that time, a total of 40 pts experienced 189 treated episodes, which is a sum total of 36 pts with 106 discrete episodes and 9 pts with 83 episodes from 9 storm events. First shock efficacy for discrete episodes was 87% and did not change significantly by rhythm type (MVT or PVT/VF P=.44), nor over time (P=.67) (Figure). Likewise, final shock efficacy for discrete episodes was 96% and did not change significantly with rhythm type (MVT or PVT/VF P=.23), nor over time (P=.87) (Figure). In the 4 episodes from 3 pts the final shock did not terminate the arrhythmias within the specified timeframe for success; in all cases the pts survived the episodes. Shock efficacy was 100% for all storm events. Time to therapy delivery (median 17.6 seconds, interquartile range (IQR) 16.3-2.3) did not change significantly by rhythm type (P=.08) nor by year (P=.32) for first shock delivery in discrete episodes, nor for first shock delivery in episodes during storm events (median 18.5 seconds, IQR 15.7-21.1; rhythm type: P=.47; year: P=.72). Conclusion The EFFORTLESS extension results demonstrate that high shock efficacy and consistent time to therapy persisted for 203 patients implanted with the subcutaneous defibrillator and followed for a median of 9.3 years.