By randomly activating or deactivating the atrial sensing function for a study, researchers sought to evaluate, in the first place, whether the atrial sensing capability of atrial sensing dipole (VDD)- implantable cardioverter-defibrillator (ICD) was helpful in atrial fibrillation (AF) detection and inappropriate therapy reduction. The study was intended to be a prospective, multicenter, open-label, randomized experiment to enroll 640 patients receiving the implantation of the VDD-ICD system. These patients had no history of clinical AF or rhythm control for AF within the previous year. Patients were given a random assignment to either the “ON” or “OFF” group for atrial sensing, with crossover being permitted throughout follow-up. During the study’s follow-up period of 2 years, the incidence of AF detection and incorrect ICD therapy would serve as the coprimary outcomes. Secondary outcomes included atrial tachyarrhythmia that was not associated with atrial fibrillation (non-AF atrial tachyarrhythmia), ventricular tachyarrhythmia with or without ICD therapy, and thromboembolic events, bleeding, hospitalization for heart failure, mortality, a composite of unfavorable cardiovascular events, and long-term stability or variability of atrial sensing. They anticipated that this trial would be able to evaluate the efficacy of a single-lead ICD system on a variety of clinical outcomes, such as the detection of atrial fibrillation (AF) and the reduction of inappropriate therapy, and would ultimately guide the selection of an ICD system.