Usefulness of an implantable loop recorder in diagnosing unexplained syncope and predictors for pacemaker implantation

Background: An implantable loop recorder (ILR) is an effective tool for diagnosing unexplained syncope (US). We examined the diagnostic utility of an ILR in detecting arrhythmic causes of US and determining which clinical factors are associated with pacemaker (PM) implantation. Methods: This retrospective, multicenter, observational study was conducted from February 2006 to April 2018 at 11 hospitals in Korea. Eligible patients with recurrent US received an ILR to diagnose recurrent syncope and document arrhythmia. Results: A total of 173 US patients (mean age, 67.6 ± 16.5 years; 107 men [61.8%]) who received an ILR after a negative conventional workup were enrolled. During a mean follow-up of 9.4 ± 11.1 months, 52 patients (30.1%) had recurrent syncope, and syncope-correlated arrhythmia was confirmed in 34 patients (19.7%). The ILR analysis showed sinus node dysfunction in 24 patients (70.6%), supraventricular tachyarrhythmia in 4 (11.8%), ventricular arrhythmia in 4 (11.8%), and sudden atrioventricular block in 2 (5.9%). Overall, ILR detected significant arrhythmia in 99 patients (57.2%) irrespective of syncope. Among patients with clinically relevant arrhythmia detected by ILR, PM implantation was performed in 60 (34.7%), an intra-cardiac defibrillator in 5 (2.9%), and catheter ablation in 4 (2.3%). In a Cox regression analysis, history of paroxysmal atrial fibrillation (PAF) (hazard ratio [HR], 2.34; 95% confidence interval [CI], 1.33-4.12; P < 0.01) and any bundle branch block (BBB) (HR, 2.52; 95% CI, 1.09-5.85; P = 0.03) were significantly associated with PM implantation. Conclusion: ILR is useful for detecting syncope-correlated arrhythmia in patients with US. The risk of PM is high in US patients with a history of PAF and any BBB.