Syncope is a common condition, especially in the elderly population, which frequently leads to presentation to an emergency department. The socioeconomic costs of syncope and its consequences are substantial and will continue to increase in an aging society. Current guidelines recommend Implantable loop recorder (ILR) in the case of an unremarkable comprehensive syncope evaluation. There are only few large studies that have investigated clinical predictors of pacemaker implantation in this patient cohort. The aim of this study was to identify clinical predictive markers for pacemaker implantation in patients with unexplained syncope who underwent ILR implantation.

The present study was a retrospective two-centre cohort study. A total of 261 patients were retrospectively analysed between 2015 and 2017 who got an ILR implantation and were followed up at least for 3 years. All patients experienced at least 1 syncope. A guideline oriented diagnostic workup was performed before implanting an ILR.  The primary end point of the study was detection of an electrocardiogram (ECG) recording in the ILR leading to pacemaker implantation. 

A total of 261 patients underwent ILR implantation. The median age of all study patients was 67.9 years and 35,3% of patients were female. Implantation of a pacemaker was required in 78 (29.9%) patients (group 1), while the rest of the patients had no indication for pacemaker implantation (group 2). Patients who received a pacemaker have been on average significantly older (71.79 ± 13.19 vs 66.37 ± 18.27; p=0.008), had lower GFR (64.09 ± 20 vs 72.73 ± 20.69; p 0.006) and lower TSH values (mU/l) (1.48 ± 1.09 vs 2.15 ± 3.72; p= 0.003). 

In terms of 12 lead resting ECG characteristics, patients who required pacemaker implantation had significantly lower heart rate (67.85 ± 12.76 versus 74.36 ± 19.31, p=0.002) and more frequent first-degree AV block (23% vs 10.9%; p= 0.013) as compared to group 2.

Furthermore, the PR interval (ms) was significantly longer in group 1 (176.09ms ± 46.55 vs 162.86ms ± 36.87; p=0.024) as compared to group 2. There were no differences regarding bundle branch blocks, QRS and QTc duration in both groups.

In terms of echocardiographic findings there were no significant differences in comparing both groups. The number of syncope episodes and the number of syncope episodes with injury consequences did not differ significantly between the two groups. 

Age >70 years, GFR (<60ml/min), TSH, AV Block first degree and heart rate (bpm) were found as clinical predictors in the univariate analysis. In the multivariate analysis age >70 years (OR 0.511; 95% CI 0.249 – 0.937; p=0.028), TSH (OR 0.707; 95% CI 0.530 – 0.944; p=0.019) and heart rate (OR 0.972; 95% CI 0.953 – 0.992; p=0.007) could be identified as independent predictors for pacemaker implantation. 

Advanced age (>70years), reduced GFR (< 60ml/min), TSH, first degree AV Block and heart rate were found to be predictive factors for bradyarrhythmias requiring pacemaker implantation in patients receiving an ILR for unexplained syncope.