Abstract: We included four trials involving a total of 579 participants. With the limitation that only two studies reported data on mortality and none of them had considered death as a primary endpoint, the meta-analysis showed no evidence of a difference in the risk of long-term mortality between participants who received ILR and those who were managed conventionally at follow-up (RR 0.97, 95% CI 0.41 to 2.30; participants = 255; studies = 2; very low quality evidence) with no evidence of heterogeneity. No data on short term mortality were available. Two studies reported data on adverse events after ILR implant. Due to the lack of data on adverse events in one of the studies' arms, a formal meta-analysis was not performed for this outcome. Data from two trials seemed to show no difference in quality of life, although this finding was not supported by a formal analysis due to the differences in both the scores used and the way the data were reported. Data from two studies seemed to show a trend towards a reduction in syncope relapses after diagnosis in participants implanted with ILR. Cost analyses from two studies showed higher overall mean costs in the ILR group, if the costs incurred by the ILR implant were counted. The mean cost per diagnosis and the mean cost per arrhythmic diagnosis were lower for participants randomised to ILR implant. Participants who underwent ILR implantation experienced higher rates of diagnosis (RR (in favour of ILR) 0.61, 95% CI 0.54 to 0.68; participants = 579; studies = 4; moderate quality evidence), as compared to participants in the standard assessment group, with no evidence of heterogeneity. Our systematic review shows that there is no evidence that an ILR-based diagnostic strategy reduces long-term mortality as compared to a standard diagnostic assessment (very low quality evidence). No data were available for short-term all-cause mortality. Moderate quality evidence shows that an ILR-based diagnostic strategy increases the rate of aetiologic diagnosis as compared to a standard diagnostic pathway. No conclusive data were available on the other end-points analysed. Further trials evaluating the effect of ILRs in the diagnostic strategy of people with recurrent unexplained syncope are warranted. Future research should focus on the assessment of the ability of ILRs to change clinically relevant outcomes, such as quality of life, syncope relapse and costs.

Plain-language summary: We searched scientific databases and found four randomised controlled trials (clinical studies where people are randomly put into one of two or more treatment groups) including 579 adults, which met our inclusion criteria. This review includes evidence identified up to April 2015. All-cause mortality (death from any cause) was no different in people who received the ILR. Loop recorders do not seem to change quality of life, although people with ILR had a significantly higher rate of diagnosis compared to participants in the standard assessment group. Moreover, data seem to show a trend towards a reduction in syncope recurrences after diagnosis in people implanted with ILR. Finally, costs were higher in the group of participants in which the ILR was implanted but the cost per diagnosis and the cost to diagnose an arrhythmia were much lower for participants randomised to ILR implant. There was low quality evidence that ILR does not change mortality if compared to a standard diagnostic assessment of people with syncope. There was moderate quality evidence that ILR increases the rate of diagnosis if compared to a standard diagnostic assessment. Future research is needed in order to clarify if ILRs can improve quality of life and reduce syncope recurrences and costs. All the included studies were funded: two of them by scientific societies, the remaining were partially supported by the ILR's manufacturers.