Background:Atrial fibrillation (AF) is the most frequent tachyarrhythmia in patients with a permanent pacemaker.Angiotensin II receptor antagonists have a protective effect against the occurrence of AF in patients with heart diseases.This study aimed to assess the effectiveness of olmesartan in the prevention of new-onset AF and AF burden in atrioventricular block (AVB) patients with dual-chamber (DDD) pacemaker implantation.Methods:This was a single-center,prospective,randomized,single-blind,controlled clinical study.A total of 116 AVB patients,who received DDD pacemakers implantation with the percentage of ventricular pacing (VP％) ≥40％ from April 22,2011 to December 24,2012,were prospectively randomized to olmesartan group (20 mg per day;n =57) or control group (n =59).Patients were followed up using pacemaker programming,12-lead electrocardiography in the intrinsic sinus rhythm,laboratory examinations,and transthoracic echocardiography at 24 months.Atrial high rate events (AHREs) were defined as 180 beats/min over a minimum of 5 min.AF burden was calculated by the number of hours with AHREs divided by the number of measurement hours.Results:Ten (17.5％) patients in the olmesartan group and 24 patients (40.7％) in the control group occurred new-onset AF,and the difference between two groups was statistically significant (P =0.04).AF burden was lower in olmesartan group than that in control group (8.02 ± 3.10％ vs.13.66 ± 6.14％,P =0.04).There were no significant differences in mean days to the first occurrence of AHREs and mean cumulative numbers of AHREs between two groups (P =0.89 and P=0.42,respectively).Moreover,olmesartan group had smaller values of maximal P-wave durations and P-wave dispersion (PD) after 24 months follow-up compared with the control group (109.5 ± 7.4 ms vs.113.4 ± 7.1 ms,P =0.00;and 40.6 ± 4.5 ms vs.43.3 ± 4.4 ms,P =0.02,respectively).Left ventricular end-diastolic diameter and left ventricular ejection fraction were not significantly different between two groups (both P ＞ 0.05).Conclusion:This study suggested that 24-month of olmesartan therapy could reduce new-onset AF and AF burden in patients with DDD pacemakers.