Background:Atrial AutoCaptureTM (ACapTM) was a new technological development that confirmed atrial capture by analyzing evoked response (ER) with a new method-paced depolarization integral ER detection-and optimized energy output to changes in the stimulation threshold.The purpose of this study was to evaluate the clinical performance ofACapTM function.Methods:This was a prospective,observational,nonrandomized two-center study.Between November 2008 and August 2014,102 patients were enrolled from two different institutions.Data were collected by case report forms at enrollment,hospital discharge,and in-office follow-ups scheduled at 1,2,3,6,and 12 months postimplantation.Results:Ambulatory ACapTM function started to become available for 20.6％ of patients at 1 day,then progressed to 30.4％ at 7 days,38.6％ at 1 month,41.6％ at 2 months,47.5％ at 3 months,53.5％ at 6 months,and 63.4％ at 1 year.The cause of the unsuccessful attempts to perform ACapTM threshold was ER/polarization ＜2:1.Availability for SD,BND,and HOCM indications had shown better results than AVB indication.For SD indication cases,feasibility was significantly better for SD with paroxysmal atrial fibrillation (pAF) than SD without pAF (78.4％ vs.35.0％ at l year,n =71,P ＜ 0.001).At each stage of the clinical follow-ups,there had been a strict conrelation between ACapTM measurements and those conducted manually with P ＜ 0.001 (n =299).Conclusions:It has been concluded that ACapTM function was safe and effective to confirm atrial threshold and reduce energy output automatically.ACapTM function is unavailable for some patients at early stages of the implantation;however,availability has been progressively increasing during follow-up.