Subcutaneous implantable cardioverter defibrillator (S-ICD) devices have demonstrated a cardioversion efficacy rate of 98% over a period of at least five years in the EFFORTLESS study—the results of which were presented in a late-breaking presentation at the 2021 European Heart Rhythm Association congress (EHRA, 23–25 April, online).
Pier Lambiase, professor of cardiology at University College London and Barts Heart Centre (London, UK), presented five-year findings from the post market S-ICD Registry, reporting no definite electrode failures or structural defects associated with the devices throughout the study, along with only 2% of the enrolled patients requiring conversion of their S-ICD to a transvenous (TV) device for pacing.
“If we look at inappropriate shocks in this cohort, 16.9% of patients had inappropriate shocks over the five-year period, with the main cause being cardiac oversensing,” he added. “Overall, there was a low burden of inappropriate shocks, particularly for atrial fibrillation [AF] and supraventricular tachycardia [SVT], at 2.9%.
“And, importantly, untreated, inappropriate sensing episodes did predict later inappropriate shocks—and this is an opportunity for reprogramming and personalising therapy for these patients.”
The EFFORTLESS S-ICD Registry (Boston Scientific) was set up to determine the long-term efficacy and final outcomes seen within patients implanted with the CE-marked S-ICD system—early-generation devices preceding routine SMARTPASS filter availability. In his presentation, Lambiase described it as the first large, multicentre registry to report five-year outcomes in patients implanted with the device, and the longest follow-up of S-ICD outcomes in a large cohort to date.
The study took place across 46 centres in 11 countries, and specifically focused on spontaneous efficacy of shock conversion for ventricular tachycardia/ventricular fibrillation (VT/VF) throughout, as well as assessing predictors of later outcomes. A total of 984 patients, with an average age of 48 years, were implanted with the S-ICD system at the beginning of the study—although patients either dying or withdrawing over the five-year period meant 703 patients ultimately completed the study. Lambiase reported a mean implant duration of 4.4 years, and a median follow-up time of 5.1 years.
The study results saw 2% of patients require conversion of their S-ICD to a TV device for pacing, with four (0.4%) of these cases being for bradycardia, seven (0.7%) for anti-tachycardia pacing for VT, and nine (0.9%) for cardiac resynchronisation therapy (CRT).
Lambiase stated that patients’ S-ICD devices underwent reprogramming for causes of their inappropriate shocks “in a significant proportion”, and although reprogramming did initially reduce the burden of inappropriate shocks earlier on in the study, this trend was less pronounced towards the end of the study period. In addition, patients who underwent post-inappropriate shock reprogramming in the first year of the trial generally had fewer inappropriate shocks in years two-to-five.
The main predictors of appropriate shocks observed in the study were previous, appropriate shock in the first year, inappropriate shocks in years two-to-five, and markers of impaired left-ventricular function, such as heart failure. Lambiase also highlighted the fact that complications in year one, however, were not a predictor of later complications.
“Importantly, arrhythmogenic right ventricular cardiomyopathy [ARVC] and ischaemic heart disease were key multivariable predictors of appropriate shocks for monomorphic VT, indicating there is a subpopulation here that could be identified—particularly if they were having more than one appropriate shock for monomorphic VT,” Lambiase added.
Regarding the maintenance of shock efficacy over the whole five-year period, first-shock efficacy was reported to be 90% for all forms of VT/VF, and the shock efficacy rate for storm episodes was 95%, while a “high level” (98%) of final shock efficacy was maintained and did not change significantly throughout the study period.
In terms of mortality, 90.7% of patients remained alive during the five-year follow-up period, with the main, multivariable predictors of mortality being left-ventricular ejection fraction (LVEF), kidney disease and diabetes, as well as all-cause shocks. Complications and defibrillation threshold testing (DFT) were not, however, identified as predictors of mortality, according to Lambiase.
And, following his presentation, when asked by one of the EHRA session’s moderators, cardiology professor Isabelle van Gelder (University of Groningen, Groningen, The Netherlands), if he foresees a future study involving “normal ICD patients” with a higher average age, Lambiase stated: “Yes, the UNTOUCHED trial already moved in that direction and, in elderly patients, other issues come into play. Renal failure, diabetes and infection risks are all higher.
“That is why I think it is very important that we open up the opportunity to implant this device in older populations—if we can be confident they are not likely to require conversion for pacing, and we have seen already that pacing requirements seem to be very low if you select the patients carefully.”