Local unipolar and bipolar electrogram criteria for evaluating the transmurality of atrial ablation lesions at different catheter orientations relative to the endocardial surface

Background: Recognition of the creation of transmural lesions (TLs) during atrial ablation procedures is important.

Objective: The purpose of this study was to characterize local unipolar electrograms (UEs) and bipolar electrograms (BEs) recorded from a TL at different catheter orientations.

Methods: In 13 porcines, 125 point-by-point ablations were performed in the smooth myocardial areas of the atria during recording of UE and BE. Catheter orientation was adjusted to be perpendicular or oblique (nonparallel; 80 sites) or parallel (75 sites) to the endocardial surface based on left atriograms.

Results: Microscopic examination revealed TLs in 54 sites and non-TLs in 71 sites. Irrespective of catheter orientation, the distal UE recorded from TLs consistently exhibited elimination of a negative deflection, whereas that from non-TLs did not. BE recorded from TLs with nonparallel catheter orientation consistently exhibited elimination of a positive deflection, whereas that with parallel catheter orientation exhibited one of two different patterns: (1) predominant attenuation (> or =75%) of the R wave at sites exhibiting QRS pattern preablation or (2) complete elimination of the R' wave at sites exhibiting RSR' pattern preablation. The heterogeneity of the patterns of morphologic change in BE at the different catheter orientations was due to the different degree of contribution of the proximal UE to BE.

Conclusion: UE and BE criteria successfully differentiated TLs from non-TLs. Different BE criteria should be applied for recognizing TL formation in different catheter orientations.