The diagnostic yield of implantable loop recorders in unexplained syncope : A systematic review and meta-analysis

Background: Guidelines recommend that implantable loop recorders (ILRs) are used in the evaluation of people with recurrent unexplained syncope in the absence of high-risk criteria, and in high-risk patients after a negative evaluation. The aim of this systematic review was to analyze the diagnostic yield of ILRs in these patients. Methods: We performed a systematic search in order to retrieve studies enrolling adults undergoing ILR implantation for undetermined syncope. The primary outcome was the overall diagnostic yield, defined as the proportion of patients with syncope recurrence and an available ILR recording or an automatic detection of a significant arrhythmia. Secondary outcomes were the proportions of patients with the specific etiologic diagnoses on the total of subjects and the proportion of an analyzable ECG recording during symptoms. We used a random effects model for the meta-analyses. Results: Forty-nine studies, enrolling 4381 subjects, were included. The overall diagnostic yield was 43.9% (95% CI=40.2%, 47.6%; I 2 =79.8%). The proportions of subjects finally diagnosed with arrhythmic syncope, ventricular arrhythmias, supraventricular arrhythmias and bradyarrhythmias were 26.5%, 2.7%, 4.9% and 18.2%, respectively. The proportion of an analyzable ECG recording during symptoms was 89.5% (95% CI=86.1%, 92.1%; 1236 subjects; 36 studies; I 2 =44.9%). Median time to diagnosis was 134days. Heterogeneity is an important limitation to be acknowledged. Conclusions: About a half of unexplained syncope subjects implanted with an ILR were diagnosed, and around 50% of them had an arrhythmia. Life-threatening arrhythmias as well as ILR complications and death due to arrhythmic events were very rare.