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Background-Radiofrequency ablation of tissues in pulmonary veins can eliminate paroxysmal atrial fibrillation. Objective-To explore the characteristics of normal pulmonary veins so as to provide more information relevant to radiofrequency ablation. Methods-20 structurally normal heart specimens were examined grossly. Histological sections were made from 65 pulmonary veins. Results-The longest myocardial sleeves were found in the superior veins. The sleeves were thickest at the venoatrial junction in the left superior pulmonary veins. For the superior veins, the sleeves were thickest along the inferior walls and thinnest superiorly. The sleeves were composed mainly of circularly or spirally oriented bundles of myocytes with additional bundles that were longitudinally or obliquely oriented, sometimes forming mesh-like arrangements. Fibrotic changes estimated at between 5% and 70% across three transverse sections were seen in 17 veins that were from individuals aged 30 to 72 years. Conclusions-The myocardial architecture in normal pulmonary veins is highly variable. The complex arrangement, stretch, and increase in fibrosis may produce greater non-uniform anisotropic properties. (Heart 2001;86:265-270) Keywords: arrhythmias; catheter ablation; fibrillation; cardiac veins Studies from various groups of investigators have suggested that certain forms of atrial fibrillation are related to the existence of an ectopic discharging focus which is frequently located within the pulmonary veins.1-4 Radiofrequency catheter ablation carried out in the pulmonary veins can eliminate paroxysmal atrial fibrillation in many cases. Stenosis of the vein is a recognised complication following catheter ablation.5 Recurrence of the arrhythmia is also a common problem.4 Both drawbacks of current techniques of catheter ablation in these patients may be avoidable if there is better understanding of the architecture of the pulmonary veins in the human heart.In this study, we explored the walls of the pulmonary veins from the venoatrial junction to the hilum in normal specimens. We then reconstructed our findings so as to provide a three dimensional impression of the architecture of the cardiac muscle, which reinforces to a varying extent the outer layer of the pulmonary veins at their junction with the left atrium. To standardise the orientation of the left and right pulmonary veins, and to emphasise the potential significance of the diVerences in the anatomical arrangements, we viewed the orifices of the veins as they would be seen in a simulated left anterior oblique projection, and used the clock face to describe the sectors of the walls. MethodsWe harvested 65 veins from 20 structurally normal heart specimens that were collected in

Triggers from the Purkinje arborization or the right ventricular outflow tract have a crucial role in initiating ventricular fibrillation associated with the long-QT and Brugada syndromes. These can be eliminated by focal radiofrequency ablation.

R ecent decades have seen rapid developments in arrhythmia treatment, especially the use of catheter ablation. Although the substrates of atrial fibrillation, its initiation and maintenance, remain to be fully elucidated, catheter ablation in the left atrium has become a therapeutic option for patients with this arrhythmia. With ablation techniques, various isolation lines and focal targets are deployed; the majority of these are anatomic approaches. It has been over a decade since we published our first article on the anatomy of the left atrium relevant to interventional electrophysiologists. 1 Our aim then, as now, was to increase awareness of anatomic structures inside the left atrium. In this review of anatomy, we revisit the left atrium, inside as well as outside, for a better understanding of the atrial component parts and the spatial relationships of specific structures. Location and Atrial WallsViewed from the frontal aspect of the chest, the left atrium is the most posteriorly situated of the cardiac chambers. Owing to the obliquity of the plane of the atrial septum and the different levels of the orifices of the mitral and tricuspid valves, the left atrial chamber is more posteriorly and superiorly situated relative to the right atrial chamber. The pulmonary veins enter the posterior part of the left atrium with the left veins located more superior than the right veins. The transverse pericardial sinus lies anterior to the left atrium, and in front of the sinus is the root of the aorta. The tracheal bifurcation, the esophagus, and descending thoracic aorta are immediately behind the pericardium overlying the posterior wall of the left atrium. Further behind is the vertebral column.Following the direction of blood flow, the atrial chamber begins at the pulmonary veno-atrial junctions and terminates at the fibro-fatty tissue plane that marks the atrioventricular junction at the mitral orifice. The walls of the left atrium are muscular and can be described as superior, posterior, left lateral, septal (or medial), and anterior, as suggested by McAlpine, 2 who drew attention to the importance of describing the heart in its anatomic position in the chest, in the orientation he termed "attitudinal," which is the appropriate terminology for cardiac interventionists. 3 The left atrium is relatively smooth-walled on its internal aspect ( Figure 1A), but its walls are not uniform in thickness. The roof or superior wall is in close proximity to the bifurcation of the pulmonary trunk and the right pulmonary artery. The thickness of its muscle component measured transmurally ranges from 3.5 to 6.5 mm (mean, 4.5Ϯ0.6 mm) in formalin-fixed heart specimens. 4 The thickness of the lateral wall ranges between 2.5 and 4.9 mm (mean, 3.9Ϯ0.7 mm). The anterior wall, related to the aortic root, ranges from 1.5 to 4.8 mm (mean, 3.3Ϯ1.2 mm) thick, but it can become very thin at the area near the vestibule ( Figure 1B) of the mitral annulus, diminishing to an average thickness of 2 mm. Importantly, there is an area of the anterio...

The variability in width and thickness of the LLR, its proximity to Marshall structures and autonomic nerves, and myofibre arrangement may be significant in the fibrillatory process and spread of AF activity.