An Underrecognized Cause of Recurrent Nocturnal Syncope with a Pacemaker: Sleep Rate Mode

Nocturnal syncope is a common presentation in the emergency department, often related to orthostatic hypotension and subsequent loss of cerebral perfusion when patients get up from sleep to use the restroom faster than their cardiac output and vascular tone can accommodate. Poor hydration status and antihypertensive medications can increase this risk. Patients with syncope who present to the emergency department with a pacemaker are usually evaluated with a pacemaker interrogation to evaluate for runs of nonperfusing rhythms (e.g., ventricular tachycardia or fibrillation). Sleep rate mode (SRM) is a relatively new feature of modern pacemakers and is not currently recognized by emergency physicians. It was implemented to accommodate more physiologic fluctuations in heart rate during rapid eye movement sleep. There is a paucity of evidence supporting the clinical benefit of SRM and similarly no documentation of prior complications of SRM in the current literature.

We report the case of a 92-year-old woman with a Medtronic Avisa pacemaker presenting with recurrent nocturnal syncope and bradycardia resulting in multiple emergency department visits. These episodes ultimately resolved by turning off SRM on her pacemaker. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: SRM is not currently flagged on interrogation report summaries provided to emergency physicians. This report highlights the importance of recognizing this mode as a potential etiology of nocturnal syncope related to chronotropic incompetence in patients with pacemakers.