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Background: 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. Clinical Trial Registration: URL https://clinicaltrials.gov Unique Identifier NCT02433379

We appreciate the authors' careful review of our manuscript and prepared the following response to their comments.The first comment is that the SmartDelay Determined AV Optimization: A Comparison to Other AV Delay Methods Used in Cardiac Resynchronization Therapy (SMART-AV) trial was underpowered to detect the additional response to atrioventricular (AV) optimization. Importantly, the authors performed a post hoc power calculation, basing their calculations on the observed fixed-group response. These calculations do not have the same validity as prospective power calculations and must be interpreted with great caution. 1 Second, the noninferiority margin of 15 mL for a left ventricular end-systolic volume difference from baseline to 6 months post-cardiac resynchronization therapy was chosen by the SMART-AV Steering Committee as reflecting a clinically meaningful difference. Moreover, the primary and secondary end points and the statistical analysis plan were reviewed with the Food and Drug Administration before the initiation of the SMART-AV trial and have been previously published in detail. 2 Third, a larger trial would always provide more power to detect smaller differences. Based on the trial design, we cannot exclude the possibility that AV optimization with either echo or the SmartDelay can lead to smaller changes in these end points. The 95% confidence limits for the median differences observed in the trial suggest that the true difference in improvement in left ventricular end-systolic volume between the echo and fixed arms is between 12 mL and Ϫ3 mL. The 95% confidence limits for the median differences observed in the trial suggest that the true difference in improvement in left ventricular end-systolic volume between the SmartDelay and fixed arms is between 11 mL and Ϫ3 mL.Finally, this trial should not be interpreted as providing evidence "that AV optimization does not work for anyone." In fact, we explicitly conclude that "these data do not exclude possible utility in selected patients who do not respond to CRT," and we provide the results of a subgroup analysis suggesting a possible benefit to AV optimization in women, as well. 3 Disclosures

Background-One variable that may influence cardiac resynchronization therapy response is the programmed atrioventricular (AV) delay. The SmartDelay Determined AV Optimization: A Comparison to Other AV Delay Methods Used in Cardiac Resynchronization Therapy (SMART-AV) Trial prospectively randomized patients to a fixed empirical AV delay (120 milliseconds), echocardiographically optimized AV delay, or AV delay optimized with SmartDelay, an electrogram-based algorithm. Methods and Results-A total of 1014 patients (68% men; mean age, 66Ϯ11 years; mean left ventricular ejection fraction, 25Ϯ7%) who met enrollment criteria received a cardiac resynchronization therapy defibrillator, and 980 patients were randomized in a 1:1:1 ratio. All patients were programmed (DDD-60 or DDDR-60) and evaluated after implantation and 3 and 6 months later. The primary end point was left ventricular end-systolic volume. Secondary end points included New York Heart Association class, quality-of-life score, 6-minute walk distance, left ventricular end-diastolic volume, and left ventricular ejection fraction. The medians (quartiles 1 and 3) for change in left ventricular end-systolic volume at 6 months for the SmartDelay, echocardiography, and fixed arms were Ϫ21 mL (Ϫ45 and 6 mL), Ϫ19 mL (Ϫ45 and 6 mL), and Ϫ15 mL (Ϫ41 and 6 mL), respectively. No difference in improvement in left ventricular end-systolic volume at 6 months was observed between the SmartDelay and echocardiography arms (Pϭ0.52) or the SmartDelay and fixed arms (Pϭ0.66). Secondary end points, including structural (left ventricular end-diastolic volume and left ventricular ejection fraction) and functional (6-minute walk, quality of life, and New York Heart Association classification) measures, were not significantly different between arms. Conclusions-Neither SmartDelay nor echocardiography was superior to a fixed AV delay of 120 milliseconds. The routine use of AV optimization techniques assessed in this trial is not warranted. However, these data do not exclude possible utility in selected patients who do not respond to cardiac resynchronization therapy. Clinical Perspective on p 2668Achieving the optimal outcome from CRT may be dependent on proper programming of the optimal atrioventricular (AV) delay. 13,14 Suboptimal AV delay programming can result in as much as a 10% to 15% decline in cardiac output. 15,16 However, the large-scale randomized clinical trials establishing the overall efficacy of CRT have differed widely in their approach to AV optimization. In the CONTAK CD trial, there was no AV optimization. 6 In contrast, the Cardiac Resynchronization-Heart Failure (CARE-HF) and Multicenter InSync Randomized Clinical Evaluation (MIRACLE) investigators used Doppler echocardiography of transmitral flow to select the optimal AV delay, 2,3,13,14,17 an approach endorsed by the American Society of Echocardiography. 18 In further contrast, the Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) investigators used an algorithm based on the i...