DUAL-CHAMBER PACEMAKERS IN PATIENTS WITH PAROXYSMAL ATRIAL-FIBRILLATION

Mode switching algorithms have been developed to avoid tracking of atr ial fibrillation (AF) or flutter (AFL) during DDD(R) pacing. Upon reco gnition of AF or AFL, the mode is switched to a non-tracking sensor dr iven mode. Mode switching to a sensor driven non-tracking mode can be triggered by a single or a number of beats. Re-synchronization to sinu s rhythm after termination of the atrial tachyarrhythmia usually occur s after several beats of sinus rhythm. Some modes switch on a beat-to- beat basis thus avoiding an inappropriate rate increase at the onset o f the tachyarrhythmia and also avoiding periods of AV dissociation dur ing re-synchronization to sinus rhythm. In the atrial tracking mode si ngle atrial premature beats or runs of atrial premature beats can give rise to an irregular rapid ventricular paced rhythm. Algorithms desig ned to avoid this by limiting the variation in R-R interval can howeve r give rise to loss of AV synchrony for several beats. The atrial sync hronization pulse algorithm is a feature capable of restoring AV synch rony promptly if the atrial synchronization interval is programmed sho rt enough.