Causes of syncopal recurrences in patients treated with permanent pacing for bradyarrhythmic syncope: findings from the SYNCOPACED registry

BACKGROUND: Few studies have examined the causes of syncope/collapse recurrences in patients with a previously implanted pacemaker for bradyarrhythmic syncope.OBJECTIVE: To assess the causes of syncope/collapse recurrences after pacemaker implantation for bradyarrhythmic syncope in a large patient population.METHODS: Prospective, multicenter, observational registry enrolling 1,364 consecutive patients undergoing pacemaker implantation for bradyarrhythmic syncope. During follow-up, the time to the first syncope/collapse recurrence was recorded. Patients with syncope/collapse recurrences underwent a predefined diagnostic work-up aimed at establishing the mechanism of syncope/collapse.RESULTS: During a median follow-up of 50 months, 213 patients (15.6%) reported at least one syncope/collapse recurrence. The risk of syncope/collapse recurrence was highest in patients who underwent implantation for cardioinhibitory vasovagal syncope (26.4%), followed by unexplained syncope and chronic bifascicular block (21.5%), cardioinhibitory carotid sinus syndrome (17.2%), atrial fibrillation needing pacing (15.5%), atrioventricular block (13.6%), and sinus node disease (12.5%) (p=0.017). The most frequent cause of syncope/collapse recurrence was reflex syncope (27.7%), followed by orthostatic hypotension (26.3%), pacemaker/lead malfunction (5.6%), structural cardiac disease (5.2%), and atrial and ventricular tachyarrhythmias (4.7 and 3.8%, respectively). In 26.8% of cases, the mechanism of syncope/collapse remained unexplained.CONCLUSION: In patients receiving a pacemaker for bradyarrhythmic syncope, reflex syncope and orthostatic hypotension are the most frequent mechanisms of syncope/collapse recurrence after implantation. Pacing system malfunction, structural cardiac diseases and tachyarrhythmias are rare mechanisms. The mechanism remains unexplained in more than 25% of patients.