Sinus rhythm R-wave amplitude as a predictor of ventricular fibrillation undersensing in patients with implantable cardioverter-defibrillator
Introduction
Historically, ventricular fibrillation (VF) has been induced during implantable cardioverter-defibrillator (ICD) implantation to ensure that the ICD will sense, detect, and defibrillate VF. Predicting the likelihood of VF undersensing without inducing VF is of limited importance if VF is induced routinely at ICD implant to test reliability of defibrillation. However, the shock strength required to defibrillate VF can be estimated without inducing VF using testing based on the upper limit of vulnerability,1 and there is an increasing clinical trend toward implanting ICDs without testing defibrillation efficacy.2, 3
Current implant guidelines state that sensing of VF should be reliable if the amplitude of the R wave recorded from the ventricular tip-ring electrogram (EGM) is at least 5 mV in sinus rhythm.4 The recommendation was developed from peak-peak values manually measured on paper strips from a pacing system analyzer, with epicardial screw-in sensing leads placed 1 cm apart, and subsequently validated in small studies using early-model integrated-bipolar and bipolar sensing5, 6, 7, 8, 9, 10 from transvenous leads.
Sinus rhythm R-wave amplitude is commonly assessed twice at ICD implant, first using the pacing system analyzer after leads are placed and then using the sinus R-wave test in the ICD after the device has been implanted. In Medtronic ICDs, the pacing system analyzer measures peak-peak amplitude and the ICD measures base-peak amplitude from a rectified signal. The goal of this study was to determine the relationship between ICD-measured, rectified, sinus rhythm amplitude and reliability of VF sensing using dedicated-bipolar, transvenous sensing leads.
Section snippets
Methods
A retrospective analysis was conducted of VF episodes from the EMPIRIC (900 patients) and WAVE (1122 patients) clinical trials.11, 12 These studies enrolled patients with Marquis dual- or single-chamber ICDs (Medtronic, Minneapolis, MN USA). Both induced and spontaneous VF episodes were examined. The EMPIRIC and WAVE clinical trials received approval of the institutional review boards of all participating centers. Patient data were de-identified for this analysis.
Induced VF undersensing vs sinus rhythm R-wave amplitude
Of the 2022 patients enrolled in the 2 studies, 1112 (55%) met the study criteria (Figure 1) and each had 1 VF episode used for the analysis. We found that 33 episodes (3%) had at least 4 undersensed ventricular intrinsic deflections during the detection of induced VF. These episodes with VF undersensing received additional analysis. There were certainly additional episodes with 1–3 undersensed deflections that were not evaluated further. Table 2 presents the total number of undersensed
Discussion
The increasing clinical trend toward implanting ICDs without inducing VF has refocused attention on using sinus rhythm R-wave measurements to predict VF undersensing.1, 2, 3, 13 Although data on the relationship between sensing in VF and RV endocardial sinus rhythm R-wave amplitude are limited and the statistical correlation is weak,8, 9 2 studies reported that sensing of VF is adequate with nominal sensitivities near 0.3 mV if the baseline R-wave amplitude is sufficiently large: ≥5 mV13 or ≥7
Conclusion
We analyzed true bipolar sensing of induced VF or spontaneous VT/VF detected in the VF zone. Sensing of VF was so reliable that clinically significant undersensing before the initial detection did not occur. There was no correlation between device-measured, rectified sinus rhythm R-wave amplitude and VF undersensing at implant or during follow-up. 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
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Cited by (0)
The clinical studies referenced in this article were funded by Medtronic, Inc.
Ms Ruetz is a former employee of Medtronic, owns stock in Medtronic, and serves as a consultant to St Jude Medical. Ms Koehler is an employee of Medtronic. Dr Brown is an employee of Medtronic and owns stock and stock options in Medtronic. Mr Jackson is an employee of Medtronic and owns stock and stock options in Medtronic. Dr Belk is a former employee of Medtronic and is currently employed by St Jude Medical; he owns stock in St Jude Medical. Dr Swerdlow serves as a consultant to MDT and St Jude Medical and has received honoraria from MDT and BSX.