Sensing issues related to the clinical use of implantable loop recorders

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Abstract
The newer insertable loop recorder device (Reveal Plus 9526, Medtronic Inc, Minneapolis MN, U.S.A.) is equipped with auto-activation capabilities. In this study we investigated whether the new device encounters sensitivity problems in the form of oversensing or undersensing. We also tested whether body position changes influence the sensed electrogram's amplitude, therefore affecting the device's autosensing ability. We enrolled 32 patients aged 58·1±11·7 years with a loop recorder implanted either in the left parasternal or in the heart's apex area, to investigate undiagnosed syncopal episodes after initial assessment. During the follow-up period (5·7±2·7 months), that began 6 months after the device implantation, we analysed 284 auto-recorded episodes (103 undersensed and 181 correctly sensed). No oversensing episodes were recorded. The recorded QRS amplitude in five different body positions: supine, left and right lateral, sitting and standing was measured. No statistically significant changes were observed in the different postures. Even when patients were divided into subgroups according to implant site or the occurrence of undersensing episodes, no significant inter- or intra-group differences of the sensed electrogram were observed. Undoubtedly this device is the current gold standard for the diagnosis of unexplained syncope. In the population we studied though, the device faced undersensing problems. Consequently, the device should be equipped with more advanced software for QRS morphology recognition, to improve the diagnostic accuracy of the recorder.