Abstract Background It is unknown whether atrial fibrillation (AF) burden varies by pacing site in patients with reactive atrial antitachycardia pacing (rATP). We aimed to compare AF burden in patients with high atrial septal pacing (HASp) via delivery catheter and right atrial appendage pacing (RAAp) in patients with sick sinus syndrome (SSS). Methods We retrospectively identified 109 patients with a history of paroxysmal AF and SSS who had received dual‐chamber pacemaker implantation between January 2017 and December 2019, of whom 39 and 70 patients had HASp and RAAp, respectively. rATP was initiated after a 1‐month post‐implantation run‐in period. Results Patients with HASp had a significantly shorter P‐wave duration during atrial pacing than those with RAAp (99.3 ± 10.4 vs. 116.0 ± 14.3 ms, p