Abstract
Syncope with bifascicular block may be caused by intermittent complete heart block, but competing diagnoses may co-exist. We tested the hypothesis that in patients with syncope and bifascicular heart block a strategy of empiric permanent pacing (PM) reduces major adverse events more effectively than acting on the results of an implantable cardiac monitor (ICM). 115 patients >50.0 y old with bifascicular block, preserved left ventricular function, and ≥1 syncope in the preceding year were randomized to receive a PM or ICM in a prospective, open label, pragmatic randomized trial. The primary outcome measure was a composite of Major Adverse Study-Related Events (MASRE) over ≥2 years up to study completion. MASRE included death, syncope, symptomatic bradycardia, asymptomatic actionable bradycardia, and device complications. Enrollment ended May 22, 2015 with follow-up ending May 22, 2017. There were 56 and 59 subjects randomized to receive a PM or implantable cardiac monitor ICM in 23 sites (17 Canadian). The PM and ICM groups were similar in age (74±9 vs 77±9 y), sex (20 vs 14 female), lifetime syncopes (medians 2), syncope in prior year (medians 2), duration of symptoms (medians 1 year), no prodrome (40/56 vs 39/59), and baseline systolic BP (137±20 vs 133±21 mmHg). 40 pts had left bundle branch block and 75 had right bundle branch block and a left hemiblock. Patients were followed for median 30 months and 21 exited the study (death 8, withdrew consent after 2 years 6, cancer 4, dementia 3). PM effectively prevented the primary outcome with end study MASRE-free survivals in PM (63%) and ICM (22%) group (figure, left panel, p < 0.001 Wilcoxon). Proportions of pts with syncope were similar in PM and ICM groups (figure, middle panel, 27 vs 31%, p=0.50, Wilcoxon). Other outcomes were far higher in ICM than PM pts: asymptomatic actionable heart block (40% vs 0%, p < 0.001), and symptomatic bradycardia (40% vs 0%, p < 0.001). Fully 35/59 ICM pts (59%) crossed over to PM. There were 5 pacemaker complications requiring reintervention. In on treatment analysis syncope-free survival was far higher in the PM group (80% vs 50%, figure, right panel, p=0.002, Wilcoxon). Syncope recurs frequently in elderly pts with few but recent syncopal spells and bifascicular block. Permanent pacing compared to ICM is a preferred strategy due to high crossover rates from ICM to PM, and on-treatment efficacy in prevention of syncope by PM.
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