Persistent sinus nodal electrograms during abnormally prolonged postpacing atrial pauses in sick sinus syndrome in humans: sinoatrial block vs overdrive suppression.

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Abstract
A transvenous electrode catheter technique was used for direct recording of bipolar sinus node electrograms during postpacing atrial pauses. Multiple repetitive local sinus node electrograms during atrial quiescence validate sinus node electrograms. Such atrial pauses with sinus node electrograms are due to sinoatrial block; atrial pauses without sinus node electrograms are due to overdrive suppression or improper recording. Eight consecutive patients were prospectively selected on the basis of a corrected sinus node recovery time greater than 1500 msec during diagnostic electrophysiologic evaluation. Six patients had atrial pauses with sinus node electrograms; three patterns of sinus node electrograms during atrial pauses were observed. We conclude that (1) sinus node electrogram recording is of value in understanding the mechanism underlying postpacing atrial pauses; (2) atrial pauses are usually (6/8) caused by sinoatrial block; (3) three patterns of sinus node electrograms are observed, thus making indirect interpretation unreliable.