Pulmonary Vein Morphology Before and After Segmental Isolation in Patients with Atrial Fibrillation

Marehiko Ueda; Hiroshi Tada; Kenji Kurosaki; Kazuhiro Itoi; Keiko Koyama; Shigeto Naito; Sachiko Ito; Issei Komuro; Shigeru Oshima; Koichi Taniguchi

Disclosures

Pacing Clin Electrophysiol. 2005;28(9):944-953. 

In This Article

Discussion

The quantitative analysis of the PV morphology performed by CT in this study demonstrated the following novel findings. (1) Shrinkage of the PV trunk was often observed in the ablated PVs, and its severity did not correlate with the changes in the LA diameter but did with the severity of the de novo PV narrowing. (2) After ablation, the reduction in the diameters of both the PV ostium and the ablation site in the ablated veins, as well as the reduction in the diameter of the PV ostium in the nonablated PVs, correlated with the reduction in the diameter of the LA after ablation. (3) Luminal reduction inside the PV after ablation occurred in a bidirectional manner, and its severity was usually greater in the supero-inferior direction than in the antero-posterior direction, with 60% of PV narrowing detected only in the supero-inferior direction. No de novo PV narrowing had a diameter reduction ≥25% only in the antero-posterior direction. (4) Narrowing of the PV was found in about 10% of PVs in the patients with AF before ablation as well as in the control subjects, and it was most often found in the LIPV. No pre-existent narrowing had a diameter reduction ≥25% only in the supero-inferior direction.

These findings indicate that an asymmetric bidirectional luminal reduction and longitudinal shrinkage of the PV are characteristic morphologic changes after ablation. Structural and reverse remodeling of the PV together with the LA remodeling may affect the changes in the PV diameter. Bidirectional viewing before and after ablation is preferable to avoid missing a pre-existent lesion or underestimating the asymmetric bidirectional reduction within the PV. Meanwhile, only bidirectional viewing after ablation can distinguish a unidirectional narrowing that can be sporadically encountered, between one that is a de novo narrowing located only in the supero-inferior direction, and one that is a pre-existent narrowing located only in the antero-posterior direction.

A recent study demonstrated that fibrocellular intimal proliferation, endovascular contraction, and elastic proliferation were responsible for PV narrowing more than 6 weeks after RF energy applications, and that endovascular contraction was observed typically at the site at which the RF energy application produced necrosis with a resulting scar formation.[10] In the present study, shrinkage of the PV trunk after ablation was not influenced by the changes in the LA size but by the severity of the PV narrowing at the ablation sites. Therefore, endovascular contraction caused by RF energy deliveries within the proximal portion of the PV might cause a longitudinal shrinkage of the PV trunk as well as PV stenosis.

The muscle sleeve over the proximal portion of the PV is distributed heterogeneously, which is predominantly in the inferior portion of the superior PVs and in the superior portion of the inferior PVs.[11] A recent study also demonstrated that the sites with electrical breakthroughs where RF energy delivery impaired the conduction between the LA and the PV were often located at the superior and inferior segments within the PV.[12] In keeping with a heterogeneous distribution of the myocardial sleeve within the proximal PV and to isolate the PV electrically from the LA, RF energy has to be applied more often at the superior and inferior segments than at the anterior and posterior segments within the PV, which may result in heterogeneous PV stenosis.

Dense fibrous connective tissue around the distal portion of the myocardial sleeve from the LA into the PV has been reported.[13] We hypothesized that the dense fibrous tissue representing the histological junction between the LA and the proper PV involving medial smooth muscle forms a pre-existent mild luminal reduction in the PV at the vicinity of the ostium. In addition, as Figure 2B shows, adjacency to the descending aorta may be associated with the greatest frequency of narrowing in the LIPV. In patients with pectus excavatum, a kinking of the LIPV has been reported.[14] The specific location of the vein lying between the LA and the spine may be related to the narrowing of the LIPV in this group (Fig. 2C).

A decrease or elimination of the recurrence of AF has been expected to develop "reverse remodeling" of the LA and PVs, resulting in restoration of the enlarged dimensions. However, few studies have ever characterized the reverse remodeling of the PVs or the relationship between the LA and the PVs after ablation. In the present study, we demonstrated that dilated PV ostia in both non-ablated and ablated PVs are reduced after ablation, and that the reduction in the diameter of the PV ostium correlates with that of the LA after ablation. These findings indicate that reverse remodeling of the PVs can occur after successful ablation and is observed with a reduction in the LA size. In addition to the histological changes caused by the RF energy delivery, reverse remodeling of the PVs may play an important role in the reduction of the diameter at the ablation site after ablation. The present study and a previous study demonstrated no significant difference in the PV trunk between the AF and the control subjects.[7] Meanwhile, Kato et al. reported that the PV trunk of the AF group was significantly larger than that of the control subjects.[5] The difference in the Results among the three studies was supposedly due to undisclosed differences in the characteristics, i.e., physical size or gender of the control subjects.

In previous articles, the severity of the reduction inside the PV was determined quantitatively using a unidirectional view. Further, a measurement or estimation of the diameter at the ablation site before ablation was not sufficiently attempted.[4,5,6] The curved MPR is a kind of three-dimensional reconstruction that allows for an integrated oblique view encompassing the whole PV lumen, trunk and branches, and has been available for quantitative evaluation of stenosis of the coronary arteries.[9,15] In the present study, we measured the PV diameters in two orthogonal directions and estimated the diameter at the ablation site in consideration of the longitudinal shrinkage retrospectively using curved MPR.

A limitation of this study was that the extensive shrinkage might have complicated the estimation of the luminal reduction or alteration in the PVs because of an underestimation of the reference diameters or deformation of the ostia. A second limitation was that we could not completely distinguish a de novo luminal reduction from a pre-existent luminal reduction. Third, in the present study, no clinical stenosis of the PVs occurred after ablation. Thus, we cannot assert whether or not unidirectional viewing missed in any way any clinical PV stenosis after ablation. Finally, the distance between the ablation site and the ostium was calculated on the assumption of a linear relationship between the trunk length and the luminal reduction of the PVs, and this assumption might not have been the case. However, as mentioned in the "Results" section, the percent shortening of the trunk length demonstrated a significant linear relationship to the luminal reduction. Therefore, we believe that the error range was very small and made no difference in the Results.


CLICK HERE for subscription information about this journal.

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as:

processing....