Sensing Performance of a New Wireless Implantable Loop Recorder: A 12-Month Follow Up Study

BACKGROUND: The implantable loop recorder (ILR) is a cost-effective tool with a high diagnostic yield in the evaluation of unexplained recurrent syncope. The Sleuth ILR (Transoma Medical, St. Paul MN, USA) is a new-generation ILR with wireless transmission capability approved by the Food and Drug Administration. We report the feasibility of achieving appropriate sensing over 1-year follow-up at the traditional midclavicular and alternative inframammary implantation sites without preimplant electrocardiogram (ECG) mapping. METHODS AND RESULTS: We studied 32 patients with unexplained syncope, aged 58.4+/-18.44 years, with an ILR implanted at the left midclavicular location (n = 17) or the left inframammary site (n = 15) over 1-year post implant. No preimplant electrocardiogram (ECG) mapping was performed. The highest R-wave amplitudes were observed at the inframammary site, but over the entire follow-up period, amplitudes were not significantly different from those at the midclavicular site. At both sites, R-wave amplitudes at the 6-month follow-up were significantly higher than those measured at 1 week. P-waves were visible in 80-90% of the patients. There was no discernible difference in P-waves (amplitude) relative to implant location. Body mass index, left ventricular ejection fraction, and age did not significantly influence the R-wave amplitude or the ability to discern P-waves. CONCLUSION: Our findings show that the Sleuth ILR implanted at both the midclavicular and inframammary locations without preimplant ECG mapping achieves acceptable "R" waves. This may simplify implantation procedures and improve patient satisfaction.