Primary Results From a Study of the Use of S-ICD in Primary Prevention Patients With Low Ejection Fraction
abstract
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Access this abstract nowBackground
The Subcutaneous ICD (S-ICD) is safe and effective for sudden cardiac death prevention. However, patients in previous S-ICD studies had fewer comorbidities, less left ventricular dysfunction and received more inappropriate shocks (IAS) than in typical transvenous (TV)-ICD trials. The UNTOUCHED trial was designed to evaluate the IAS rate in a more typical, contemporary ICD patient population implanted with the S-ICD using standardized programming and enhanced discrimination algorithms.
Methods
Primary prevention patients with left ventricular ejection fraction (LVEF) ≤ 35% and no pacing indications were included. Generation 2 or 3 S-ICD devices were implanted and programmed with rate-based therapy delivery for rates ≥ 250 beats per minute (bpm) and morphology discrimination for rates ≥200 and < 250 bpm. Patients were followed for 18 months. The primary endpoint was the IAS free rate compared to a 91.6% performance goal, derived from the results for the ICD-only patients in the MADIT-RIT study. Kaplan-Meier analyses were performed to evaluate event-free rates for IAS, all cause shock, and complications. Multivariable proportional hazard analysis was performed to determine predictors of endpoints.
Results
S-ICD implant was attempted in 1116 patients and 1111 patients were included in post-implant follow-up analysis. The cohort had a mean age of 55.8±12.4 years, 25.6% women, 23.4% black race, 53.5% with ischemic heart disease, 87.7% with symptomatic heart failure and a mean LVEF of 26.4±5.8%. Eighteen-month freedom from IAS was 95.9% (Lower confidence limit LCL 94.8%). Predictors of reduced incidence of IAS were implanting the most recent generation of device, using the three-incision technique, no history of atrial fibrillation, and ischemic etiology. The 18-month all cause shock free rate was 90.6% (LCL 89.0%), meeting the prespecified performance goal of 85.8%. Conversion success rate for appropriate, discrete episodes was 98.4%. Complication free rate at 18 months was 92.7%.
Conclusions
This study demonstrates high efficacy and safety with contemporary S-ICD devices and programming despite the relatively high incidence of co-morbidities in comparison to earlier S-ICD trials. The inappropriate shock rate (3.1% at one year) is the lowest reported for the S-ICD and lower than many TV ICD studies using contemporary programming to reduce IAS.
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Additional Info
Primary Results From the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) Trial
Circulation 2020 Oct 19;[EPub Ahead of Print], MR Gold, PD Lambiase, MF El-Chami, RE Knops, JD Aasbo, MG Bongiorni, AM Russo, JC Deharo, MC Burke, J Dinerman, CS Barr, N Shaik, N Carter, T Stoltz, KM Stein, AJ Brisben, LV BoersmaFrom MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
Leads represent the weak link in cardiac implantable electronic devices (CIEDs) because they reside in a hostile intravascular environment, twisting and bending 70 or more times each minute over many years. Despite manufacturers’ attempts to replicate that stress in prefabrication testing to create the most resilient lead, nothing can really replace the stress of the real-world environment. Hence, the development of the leadless pacemaker, a bullet-sized and shaped invention implanted in the right ventricular wall without a lead, which has achieved such clinical success.
For implantable cardiac defibrillators (ICDs), the challenge has been different, and as Gust Bardy, the inventor of the subcutaneous ICD (S-ICD), wrote in this journal several weeks ago, “The S-ICD concept first arose 29 years ago following the death of a young female patient of mine who had a transvenous ICD but died of untreated VF. Her ICD properly diagnosed VF but failed to convert the VF because the defibrillation coil cable failed. At that time, I imagined that it would be possible to avoid transvenous leads and the risk of lead failure given that most VF patients did not need pacing.”
The study by Gold et al reaffirms the success of the S-ICD as a safe and effective CIED to prevent sudden cardiac death from a ventricular tachyarrhythmia. The UNTOUCHED trial was designed to determine the rate of inappropriate shocks (IAS) as primary prevention in patients with left ventricular ejection fraction (LVEF) ≤35% and no pacing indications. The primary endpoint was the IAS-free rate compared with a 91.6% outcome from the results in the MADIT-RIT study. In 1111 patients analyzed post implant (mean age, 56 years; 25% women; 53.5% ischemic heart disease; mean LVEF, 26.4%), they found a 96% 18-month freedom from IAS. The conversion success rate was 98.4%, and the complication-free rate at 18 months was 92.7%. The authors noted that the “study demonstrates high efficacy and safety with contemporary S-ICD devices and programming despite the relatively high incidence of comorbidities in comparison with earlier S-ICD trials. The inappropriate shock rate (3.1% at 1 year) is the lowest reported for the S-ICD and lower than many TV ICD studies using contemporary programming to reduce IAS.”
Bardy concluded in his report that “I can only find joy in this 29-year odyssey that was birthed from tragedy but eventually grew into a public health benefit. Countless colleagues worked endless hours and directed considerable effort to ensure that cardiac patients live longer and live better.” Indeed, he should feel proud that his invention has made such a beneficial impact in treating one of the world’s scourges, sudden cardiac death.