Abstract
The significance of fragmented activity obtained from the atrium during electrophysiologic study (EP study) was confirmed since it was al ways observed just at the onset of fi brillation. It was preceded by extra stimuli or atrial flutter, and the initial site of fragmentation varied from case to case. The premature-stimu lus-induced widening of the atrial wave was observed in some cases who had normal size of atrium and no heart failure. The widening was aug mented by administration of vera pamil but not by procainamide, suggesting that for such widening or fragmented activity, slow-fiber-medi ated conduction seems to be responsi ble. One case with intraatrial reen trant tachycardia developed fragmentation lasting for 1.0 second after verapamil.
Therefore, some apparently nor mal atria may have a subclinical elec trophysiologic abnormality that can be disclosed by premature stimula tions or verapamil.
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