Presyncopal episodes after implantation of dual-chamber pacemaker programmed in SafeR pacing mode.

On arrival to the emergency department, the patient had no symptoms. Laboratory studies and chest X-ray showed no significant findings, and the electrocardiogram revealed sinus rhythm at 58 bpm and a normal PR interval (160 ms) with left anterior fascicular block and complete right bundle branch block, both previously known. Device interrogation showed how all nine presyncopal episodes coincided with nine checks to detect intrinsic conduction that caused pauses>2.5 s (Figure 1). The pacemaker was adjusted to permanent DDD mode, resolving the symptomatology. Figure 1 Automatic switch to AAI mode after 100 paced ventricular cycles related to presyncopal symptoms. As the atrioventricular block is still present, the third-degree AVB criterion applies and the algorithm makes the switch to DDD mode.