Clinical predictors of very low defibrillation threshold in the extravascular ICD

Abstract

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Medtronic, Inc. Background The extravascular ICD (EV ICD) is a 40J device utilising a lead placed behind the sternum and a subcutaneous can in the axilla to achieve defibrillation efficacy, size, and predicted longevity comparable to transvenous devices, as well as providing pause prevention and antitachycardia pacing. In the worldwide EV ICD Pivotal Study, 98.7% of 302 patients completed the defibrillation (DF) testing protocol with a safety margin of ≥10J. In 71.5% of patients, defibrillation was successful at lower energies (20J or 15J). Factors associated with lower energy defibrillation in EV ICD patients have yet to be determined. Purpose In this analysis we examine what factors are associated with very low DF thresholds (safety margin ≥20J). Methods Multivariate analysis was performed to look for clinical and implant predictors in patients with success at very low energies (15J or 20J, n = 216) versus those in whom either success was achieved at higher energies (2x 30J before or after polarity changes/revisions, n = 82), or DF testing failed (n=4) or was incomplete (n = 4). Results 24 variables were examined: 18 pre-implant clinical factors (including gender, body measurements, aetiology, LV ejection fraction, medications) and 6 peri-implant electrical measurements. Univariate analysis identified 5 clinical factors and 4 implant measurements as predictors of defibrillation success at very low energy; multivariate analysis with a gate of p <0.1 found 6 factors to be independent predictors (see table). Conclusions Certain pre-implant clinical factors and implant details are independent predictors of successful defibrillation at very low energies. If confirmed, these findings suggest that in many cases DF testing at EV ICD implant may not be necessary.