Predictors of pacemaker requirement in patients receiving implantable loop recorders for unexplained syncope: a systematic review and meta-analysis.

Background Implantable loop recorders (ILR) are increasingly used to evaluate patients with unexplained syncope. Identification of all predictors of bradycardic syncope and consequent permanent pacemaker (PPM) insertion is of substantial clinical interest, as patients in the highest-risk category may benefit from upfront pacemaker insertion. Objectives We performed a systematic review and meta-analysis to identify risk predictors for PPM insertion in ILR recipients with unexplained syncope. Methods An electronic database search (MEDLINE, Embase, Scopus, Cochrane) was performed in June 2023. Studies evaluating ILR recipients with unexplained syncope and recording risk factors for eventual PPM insertion were included. A random-effects model was used to calculate the pooled odds ratio (OR) for clinical and ECG characteristics with respect to future PPM requirement. Results 8 studies evaluating 1007 ILR recipients were included. 268 patients (26.6%) underwent PPM insertion during study follow-up. PPM recipients were older (mean age 70.2±15.4 vs 61.6±19.7 years, p<0.001). PR prolongation on baseline ECG was a significant predictor of PPM requirement (pooled OR 2.91, 95% confidence interval [CI] 1.63-5.20). The presence of distal conduction system disease, encompassing any bundle-branch or fascicular block, yielded a pooled OR of 2.88 for PPM insertion (CI 1.53-5.41). Injurious syncope and lack of syncopal prodrome were not significant predictors of PPM insertion. Sinus node dysfunction accounted for 62% of PPM insertions, while atrioventricular (AV) block accounted for 26%. Conclusion Approximately one-quarter of ILR recipients for unexplained syncope require eventual PPM insertion. Advancing age, PR prolongation and distal conduction disease are the strongest predictors for PPM requirement.