Published online before print February 24, 2005, 10.1148/radiol.2351041729
(Radiology 2005;235:49-50.)
Clinician’s Commentary
Tristram D. Bahnson, MD
Details about pulmonary vein anatomy have become clinically important for catheter ablation in patients with atrial fibrillation. Initial reports suggested that in most patients with lone atrial fibrillation, which is atrial fibrillation that occurs in the absence of any evident heart disease, atrial fibrillation is initiated by rapid nonsustained atrial tachycardia that originates in regions of the left atrium near the pulmonary vein orifices (1). Ablation or isolation of these regions can cure atrial fibrillation (2,3). Catheter ablation for atrial fibrillation has evolved rapidly, and most large centers currently employ anatomically based radiofrequency catheter ablation targeting tissue around the pulmonary vein orifices with or without additional ablation of left atrial tissue (3,4). Imaging with contrast material–enhanced computed tomography (CT) or magnetic resonance (MR) imaging before the procedure (5–7), and intracardiac ultrasonography (8,9) or electroanatomic mapping during the procedure (3), have proved important for recognition of anatomic variations in the pulmonary venous system and to guide localization of ablation to lesions. Newer techniques are being developed to import segmented CT or MR image reconstructions of the left atrium and pulmonary veins into ablation mapping systems to facilitate the ablation procedure. Thus, the population with atrial fibrillation will likely yield the largest pool of patients who will undergo CT or MR imaging of the left atrium and pulmonary veins in the near term.
In this issue, Kim et al (10) report pulmonary vein size and shape in 104 normal subjects who underwent contrast-enhanced CT to exclude pulmonary embolus. Kim et al (10) found that pulmonary veins have an ovoid shape that is most prominent for left-sided veins. Further, they reported that the left inferior pulmonary vein often demonstrated narrowing at the pulmonary vein–left atrium junction. These findings are potentially important for two reasons. First, the apparent normal anatomic characteristics of the left pulmonary veins, especially the left inferior pulmonary vein, could mimic postablation stenosis. Second, findings in previous reports demonstrate that venous stenosis or increased flow after catheter ablation, when observed with serial imaging, usually involves the left-sided veins, particularly the left inferior pulmonary vein (2,9,11). The reported ovoid shape and ostial narrowing of the left pulmonary veins, if generalizable to patients with atrial fibrillation, could help explain these observations. For example, ostial narrowing of the left inferior pulmonary vein could potentially facilitate unwanted ablation delivery deep in the pulmonary vein beyond the area of narrowing by stabilizing the catheter tip at this location; catheter ablation within the pulmonary veins has been associated with stenosis rates as high as 45% (12). In addition, an ovoid venous ostium could result in contact of the ablation catheter with the anterior and posterior rim of the os simultaneously to produce more extensive tissue contact and ablation than intended when the catheter is oriented out of plane to the long axis of the vein. Though speculative, either occurrence could explain, in part, the observed tendency for stenoses to occur in the left veins after ablation. Alternative hypotheses have not been excluded.
An important qualification of this study relates to generalizability of the data to other patient groups, such as those with atrial fibrillation. Previous studies in which patients with atrial fibrillation were compared with patients without atrial fibrillation clearly demonstrated significant differences in pulmonary veins between these groups; pulmonary vein size was larger in patients with atrial fibrillation who underwent either CT (5) or MR imaging (6,13). The current study (10) did not include patients with atrial fibrillation or patients with a left common pulmonary vein trunk, which is a pulmonary vein anatomic variant often seen in patients with atrial fibrillation (6,7) and others (14).
In conclusion, Kim et al (10) added to our understanding of pulmonary vein anatomy and raised questions that may be relevant to catheter ablation for atrial fibrillation if further data confirm generalization to the population of patients with atrial fibrillation. Results of the current study indicate variable pulmonary vein size, ovoid shape, and baseline ostial narrowing. Taken together with results in previous studies, these findings highlight the potential pitfalls of making an assessment about catheter ablation– induced narrowing or occlusion of pulmonary veins without direct comparison with findings at a preprocedure imaging study.
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FOOTNOTES
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See also the article by Kim et al
in this issue.
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REFERENCES
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- Purerfellner H, Cihal R, Aichinger J, et al. Pulmonary vein stenosis by ostial irrigated-tip ablation: incidence, time course, and prediction. J Cardiovasc Electrophysiol 2003; 14:158-164.[Medline]
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