Coupled Pacing and Coupled Pacing with Concealed Conduction

In the case reported coupled pacing via an intracardiac catheter electrode was undertaken and continued for 28 days in order to slow the rapid ventricular response in atrial fibrillation, refractory to drug management and cardioversion. A new phenomenon was observed in which the coupled stimulus caused cardiac cycle prolongation but elicited neither a mechanical nor a propagated electrical ventricular response. Possible mechanisms of this phenomenon are discussed. Stimulation of the bundle of His or a bundle branch with retrograde, concealed conduction in the A-V node and simultaneous antegrade concealed conduction and block are suggested as the most likely. When this phenomenon was produced after each consecutive spontaneous depolarization, a reduction in ventricular rate resulted without the production of coupled extrasystolic ventricular depolarizations. This constituted a new coupled pacing technique, termed "coupled concealed pacing." The long-term effects of this technique and of conventional coupled pacing and paired stimulation in this patient are also reported.