Prevention of Syncope Through Cardiac Pacing in Patients With Bifascicular Block and Syncope of Unexplained Origin: The PRESS Study

Study Questions:

Do pacemakers prevent syncope in patients with bifascicular block?


The subjects of this multicenter randomized trial were 101 patients (mean age 77 years) with bifascicular block and ≥1 episode of unexplained syncope in the prior 6 months. A dual-chamber (DDD) pacemaker was implanted in all patients. The patients then were randomly assigned in single-blind fashion either to DDD pacing with a lower rate limit of 60 pulses/minute (ppm) (n = 52) or to a control group (back-up pacing at 30 ppm, n = 49). The primary endpoint was a composite of syncope, presyncope, or episodes of symptomatic atrioventricular block (AVB).


During 2 years of follow-up, the primary endpoint occurred significantly less often in the DDD group (13.5%) than in the control group (32.6%). During the course of the study, 14/101 patients (14%) developed a class I indication for permanent pacing, most often for symptomatic AVB (10/14 patients).


The authors concluded that DDD pacing reduces the risk of recurrent syncope/near-syncope/symptomatic AVB in patients with bifascicular block and unexplained syncope.


This study shows that DDD pacing is of value in patients with unexplained syncope and a left bundle branch block or right bundle branch block plus left anterior or left posterior hemiblock. Of note is that there was not a significant difference in the incidence of syncope between the DDD pacing group and the control group. This may be because the study was underpowered to detect a difference in syncope as a sole endpoint and/or because pacing at 30 ppm was sufficient to prevent syncope in some patients in the control group.

Clinical Topics: Arrhythmias and Clinical EP, Implantable Devices

Keywords: Cardiac Pacing, Artificial, Syncope, Single-Blind Method

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