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Background: In patients with implantable cardioverter-defibrillators (ICDs), inappropriate therapies (ITs) are often caused by supraventricular tachyarrhythmias (SVTs)., Objective: We aimed to estimate the incidence of IT in modern single-lead ICDs., Methods: The THINGS study enrolled patients with single-lead ICDs with 2 SVT discrimination modalities: dual chamber (DC) with an atrial floating dipole or single chamber (SC) with morphology criterion. All devices were programmed with 2-zone therapy: ventricular tachycardia (VT) zone from 170 beats/min with ≥15 seconds (≥36 beats) detection time and SVT discriminators; and ventricular fibrillation (VF) zone from 214 beats/min with ≥7 seconds (≥24 beats) detection time. The primary end point was the first occurrence of IT, adjudicated by an independent board., Results: A total of 526 patients (median age, 66 years; 83% male), 183 (34.8%) with DC and 343 (65.2%) with SC discrimination, were observed for a median of 2.2 years. The incidence rate of IT was 4.2% (95% confidence interval [CI], 2.7%-6.4%) at 1 year and 7.1% (95% CI, 5.0%-9.9%) at 2 years. Younger age (adjusted hazard ratio, 0.97; 95% CI, 0.95-0.99; P = .013) and history of atrial fibrillation (adjusted hazard ratio, 2.67; 95% CI, 1.30-5.46; P = .007) were significantly associated with increased IT risk. In a propensity score-matched comparison, DC discrimination showed a trend toward reduced IT rates compared with SC discrimination in the VT zone (1-year incidence, 1.8% vs 3.5%; P = .105)., Conclusion: High-rate VF cutoff and prolonged detection time programming resulted in a low IT rate in single-lead ICD patients with modern SVT discriminators. A trend favoring the DC system was observed in the VT zone., Competing Interests: Disclosures Mauro Biffi has held educational activity and participated in speakers bureau on behalf of Abbott, Boston Scientific, Biotronik, Medtronic, and Philips. Matteo Ziacchi has held educational activity and participated in speakers bureau on behalf of Medtronic., (Copyright © 2024 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)