Background: For many patients, sudden cardiac arrest (SCA) risk is elevated temporarily. Wearable cardioverter-defibrillators (WCDs) can monitor and treat SCA during these temporary periods. Traditional WCDs can be uncomfortable, require frequent maintenance, and cannot be used when showering, resulting in poor compliance and avoidable SCA deaths. The Jewel is a novel, water-resistant patch-wearable cardioverter-defibrillator (P-WCD) with a machine learning detection algorithm designed to improve compliance and protection against SCA., Objectives: This study aims to demonstrate the safety and clinical effectiveness of a novel P-WCD., Methods: The Jewel IDE Study, a prospective, single-arm study conducted at 30 U.S. sites, enrolled patients at SCA risk due to ventricular tachycardia/ventricular fibrillation who were not candidates for or refused an implantable defibrillator. The primary safety endpoint was <15% patients with clinically significant cutaneous adverse device effects and the primary effectiveness endpoint was <2 inappropriate shocks/100 patient-months. Secondary endpoints were ≥1 successful ventricular tachycardia/ventricular fibrillation conversion and wear time compliance of >14.1 h/d., Results: A total of 305 patients (mean age: 57.9 years; 30.2% female, 27.9% non-White) were enrolled, of which 290 had available device data. The clinically significant cutaneous adverse device effect rate was 2.30% (upper 1-sided 98% CI: 4.80); none were severe. No device-related deaths or serious adverse events were reported. The inappropriate shock rate was 0.36/100 patient-months (upper 1-sided 98% CI: 1.53). Of 11 shocks in 9 patients, 9 shocks were adjudicated to be appropriate. Eight of 9 shocks were successful with a single shock. Median wear time compliance was 23.5 (20.7-23.9) h/d., Conclusions: The novel P-WCD is a safe and effective WCD with high patient compliance. There were no deaths due to noncompliance and a high number of successful conversions (Jewel IDE study [A Clinical Evaluation of the Jewel P-WCD in Subjects at High Risk for Sudden Cardiac Arrest]; NCT05201495)., Competing Interests: Funding Support and Author Disclosures The Jewel IDE trial was conducted with support from Element Science, Inc. The sponsor was responsible for site selection, data monitoring, and overall clinical trial management. All statistical analyses were performed by an independent statistician. Dr Hummel has received consulting fees from Medtronic, Volta Medical, S4 Medical, Abbott Medical, and Element Science. Dr Houmsse has received speaker fees from Zoll. Dr Tomassoni has received speaker fees from Zoll. Ms Mathews and Drs Eapen and Kumar are employed by and stockholders of Element Science, Inc. Dr Thakkar was a Clinical Affairs Fellow at Element Science, Inc. Dr Kumar is a stockholder of iRhythm Technologies. Dr Mehran has received institutional research payments from Abbott, Abiomed, Affluent Medical, Alleviant Medical, Amgen, AM-Pharma, Arena, AstraZeneca, AtriCure Inc, Biosensors, Biotronik, Boston Scientific, Bristol Myers Squibb, CardiaWave, CeloNova, CERC, Chiesi, Concept Medical, Cytosorbents, Daiichi-Sankyo, Duke, Element Science, Essential Medical, Faraday, Idorsia Pharmaceuticals, Janssen, MedAlliance, Mediasphere, Medtelligence, Medtronic, MJH Healthcare, Novartis, OrbusNeich, Penumbra, PhaseBio, Philips, Pi-Cardia, PLx Pharma, Population Health Research Institute, Protembis, RecCor Medical Inc, RenalPro, RM Global, Sanofi, Shockwave, Vivasure, and Zoll; and has received personal fees from Cardiovascular Research Foundation (CRF), Cordis, Daiichi-Sankyo Brasil, E.R. Squibb & Sons, Esperion, Europa Group, Gaffney Events, Educational Trust, Henry Ford Health Cardiology, Ionis Pharmaceuticals, MedCon International, Novartis, NovoNordisk, PeerView Institute for Medical Education, TERUMO Europe N.V., Vectura, VoxMedia, WebMD, IQVIA, Radcliffe, and TARSUS Cardiology. Dr Butler has received consulting fees from Abbott, American Regent, Amgen, Applied Therapeutic, AskBio, Astellas, AstraZeneca, Bayer, Boehringer Ingelheim, Boston Scientific, Bristol Myers Squibb, Cardiac Dimension, Cardiocell, Cardior, CSL Bearing, CVRx, Cytokinetics, Daxor, Edwards, Element Science, Faraday, Foundry, G3P, Innolife, Impulse Dynamics, Imbria, Inventiva, Ionis, Lexicon, Lilly, LivaNova, Janssen, Medtronics, Merck, Occlutech, Owkin, Novartis, Novo Nordisk, Pfizer, Pharmacosmos, Pharmain, Pfizer, Prolaio, Regeneron, Renibus, Roche, Salamandra, Sanofi, SC Pharma, Secretome, Sequana, SQ Innovation, Tenex, Tricog, Ultromics, Vifor, and Zoll. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)