Abstract 2495: Sinus Rhythm R-wave Amplitude Does Not Predict Undersensing of Ventricular Fibrillation by Implantable Cardioverter-Defibrillators
Background: Ventricular fibrillation (VF) is induced at implantable cardioverter-defibrillator (ICD) implants to test VF sensing and defibrillation. Based on limited data from several publications, chronic VF sensing should be reliable if the amplitude of the sinus R-wave is at least 5 mV at implant, but this has never been rigorously tested. Increased interest in inductionless implants has brought new attention to the necessity of VF sensing tests.
Methods: We reviewed stored tip-ring electrograms from true bipolar leads of first episodes of induced VF recorded at a sensitivity of 1.2 mV in two clinical trials of ICDs (n=1177 patients). Undersensing was defined as failure to sense 4 or more VF depolarizations in a window of 18 VF electrograms. Detection delay was defined as a delay >5 s caused by undersensing. We also reviewed all spontaneous episodes of true VF or ventricular tachycardia detected in the VF zone during follow-up.
Results: Undersensing caused by variations in signal amplitude or low-frequency electrograms occurred in 36 of 1177 induced VF episodes (3%), with detection delay occurring in only 1 episode (0.08%) with a sinus R-wave of 13.7 mV. There was no significant difference between the R-wave amplitudes of episodes with and without undersensing (p=0.952) [Table⇓]. R waves <5 mV were slightly but not significantly more common in episodes with undersensing vs. those without: 8 of 36 (22%) vs. 173 of 1141 (15%), p=0.25. Importantly, neither undersensing nor delay occurred in any of 1236 spontaneous episodes of ICD-detected VF.
Conclusions: Clinically significant undersensing of VF is rare at implant and follow-up of modern ICD systems with true bipolar sensing. R-wave amplitude at implant does not correlate with undersensing of VF.