Clinical characteristics associated with bradycardia and asystole in patients with syncope undergoing long-term electrocardiographic monitoring with implantable loop recorder.

Background: The aim of this retrospective single center cohort study was to assess the occurrence of bradycardia during implantable loop recorder (ILR) monitoring in patients with unexplained syncope and negative conventional testing and to identify clinical predictors of bradycardia and pacemaker implantation.
Methods: An ILR was implanted in 112 patients (31 men, 81 women, mean age 64 ±13 years) with syncope which was not explained after conventional diagnostic work-up. Clinical variables were compared between patients with and without pacemaker implantation.
Results: A diagnosis was made in 67 patients (60%), including non-arrhythmic (vasodepressor) syncope (27 patients), sinus bradycardia or asystole (23 patients), atrioventricular (AV) block (14 patients) and bradycardic atrial fibrillation (3 patients). The mean time to diagnosis was 233 ± 282 days. A pacemaker was implanted in 40 patients (36%). Male gender, age above 65 years, hypertension, presence of structural heart disease, absence of prodromal symptoms, trauma secondary to syncope, asymptomatic sinus bradycardia and first-degree AV block were clinical predictors of pacemaker implantation in univariate analysis. Of the independent predictive factors three remained significant in multivariate analysis: absence of prodromal symptoms before the loss of consciousness (odds ratio OR 3.38, p = 0.01, 95% confidence interval CI 1.24-9.20), male gender (OR 3.22, p = 0.01, 95% CI 1.26-8.20) and age >65 years (OR 2.94, p = 0.02, 95% CI 1.14-8.33).
Conclusions: In patients undergoing ILR implantation bradycardia is a frequent finding despite the negative conventional diagnostic testing. Absence of prodromal symptoms, male gender and age >65 years are risk factors for bradycardia and pacemaker implantation.