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  • Title: Sinus rhythm R-wave amplitude as a predictor of ventricular fibrillation undersensing in patients with implantable cardioverter-defibrillator.
    Author: Ruetz LL, Koehler JL, Brown ML, Jackson TE, Belk P, Swerdlow CD.
    Journal: Heart Rhythm; 2015 Dec; 12(12):2411-8. PubMed ID: 26272520.
    Abstract:
    BACKGROUND: Ventricular fibrillation (VF) is induced during implantable cardioverter-defibrillator (ICD) implantation to ensure that the ICD will sense, detect, and defibrillate VF. ICD implant guidelines state that the amplitude of the sinus rhythm R wave recorded from the ventricular electrogram should have amplitude ≥5 mV. No study has tested the relationship between sinus rhythm R-wave amplitude and VF sensing using modern, transvenous sensing electrodes. OBJECTIVE: The goal of this study was to determine whether there is a sinus rhythm R-wave amplitude cutoff that can be used to determine which patients are not at risk of VF undersensing. METHODS: A retrospective analysis of induced and spontaneous VF episodes from 2 clinical trials with 2022 patients was performed. Episodes with undersensing during the initial detection of VF were identified, and the distribution of sinus rhythm R-wave amplitudes for patients with and without VF undersensing was analyzed. RESULTS: Only 3% of analyzed induced VF episodes were considered to have VF undersensing, and none had clinically significant detection delays. There was no correlation between device-measured, rectified sinus rhythm R-wave amplitude and VF undersensing at the time of implantation or during follow-up, although <4% of patients had sinus rhythm R-waves with amplitude <3 mV. CONCLUSION: We analyzed true bipolar sensing of induced VF or spontaneous ventricular tachycardia/VF detected in the ICD VF zone. Sensing of VF was so reliable that clinically significant undersensing did not occur. Our findings do not support any recommended minimum sinus rhythm R wave to ensure reliable sensing of VF or the necessity of inducing VF to verify sensing for rectified sinus rhythm R-waves with amplitude ≥3 mV.
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