Characterization of slow conduction in the common type of atrial flutter--using transient entrainment.

To characterize slow conduction of the common type of atrial flutter (common AF), in which excitation wave propagated in a counterclockwise fashion, transient entrainment during the distal high lateral right atrium (HRAd) pacing and during the proximal coronary sinus (CSp) pacing was studied in 7 patients with common AF. In transient entrainment of common AF, conduction time from stimulus to CSp during HRAd pacing was always longer than that from stimulus to HRAd during CSp pacing. It was also longer than that from stimulus to CSp during HRAd pacing in 5 control patients without common AF in sinus rhythm. Return cycles at HRA and CS after cessation of rapid pacing during transient entrainment were studied. In HRAd pacing, return cycle at the proximal high lateral right atrium was almost equal to the pacing cycle length, or almost equal to or slightly shorter than the flutter cycle length (AFCL). Return cycle at CSp was almost equal to AFCL. In CSp pacing, return cycle at the distal coronary sinus was much longer than AFCL and increased at progressively shorter pacing cycle lengths. In conclusion, slow conduction was demonstrated in the lateral limb (from HRA laterally to CS) of the reentrant circuit in common AF, but it did not exhibit decremental conduction property. Return cycle at an endocardial recording site after transient entrainment in common AF does not always exhibit an uniform pattern, affected by the relative location of and the distance between the recording site, the pacing site, the reentrant circuit and the area of slow conduction.