Key result
High-voltage intracardiac biphasic shocks decreased unipolar and bipolar electrogram amplitudes by ~20% and dV/dt by ~30%, with recovery taking approximately 60 seconds.
Why the study?
Do high-voltage intracardiac shocks alter local electrogram characteristics in humans?
RCT (n=29)
Random order
Do high-voltage intracardiac shocks alter local electrogram characteristics in humans?
p-value: p=NS
Intracardiac shocks transiently decrease electrogram amplitude and dV/dt, potentially explaining the failure of transvenous defibrillators to redetect ventricular fibrillation after an unsuccessful shock.
Transient post-shock electrogram attenuation may impair arrhythmia sensing; hypothesis-generating for transvenous defibrillator VF redetection failure.
INTRODUCTION: Transvenous defibrillators may have difficulty sensing ventricular fibrillation following an unsuccessful shock. This study was undertaken to characterize the changes that occur in intracardiac electrograms following a defibrillator shock that may contribute to the failure to redetect arrhythmias. METHODS AND RESULTS: Unipolar and bipolar electrogram recordings were made during sinus rhythm before and following monophasic and biphasic test shocks delivered in random order through a single lead defibrillator system in 15 patients. An additional 14 patients received only a biphasic shock. Electrogram amplitude, dV/dt, and activation recovery time were determined. Following biphasic shocks, unipolar electrogram amplitude decreased by a mean of 19.6% and the bipolar amplitude by a mean of 20.8% (P = NS). The mean dV/dt in the unipolar recordings decreased by 30.7% and in the bipolar recordings decreased by 33.0% (P = NS). Time constants for recovery were approximately 60 seconds. Reduction in dV/dt was greater when the shocking coil was closer to the distal sensing electrode. There was no significant influence of shock waveform (monophasic vs biphasic), recording type (unipolar vs bipolar), or clinical variables on the change in electrogram characteristics. CONCLUSION: Changes in intracardiac electrograms following defibrillator shocks through transvenous leads are seen with shocks delivered in sinus rhythm and may be related to the proximity of the shocking coil to the distal sensing electrode.
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Smith et al. (1996) conducted an RCT in Patients undergoing transvenous defibrillator testing (n=29). High-voltage intracardiac shock (monophasic and biphasic) vs. Baseline (pre-shock) and monophasic vs biphasic was evaluated on Electrogram amplitude and dV/dt (p=NS). High-voltage intracardiac biphasic shocks decreased unipolar and bipolar electrogram amplitudes by ~20% and dV/dt by ~30%, with recovery taking approximately 60 seconds.
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