Architecture of the pulmonary veins: relevance to radiofrequency ablation

Abstract

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.

Figures

Figure 1

(A) Longitudinal section through the left atrium showing a common orifice (open arrows) to the left pulmonary veins. (B) Another heart sectioned transversely and viewed from above to show the entrances of the four pulmonary veins. Note the common venous orifice (open arrow) on the left and the relation of the superior caval vein to the right superior pulmonary vein.

Figure 2

Graphic reconstructions of nine pulmonary veins with the venous wall (white) removed from the endothelial aspect to show the extensions of the muscular sleeves (pale grey). The bars represent 2 mm along the length of each vein. The unhatched areas of pale grey represent circularly or spirally arranged myocytes; hatched areas represent longitudinal or oblique myocytes. Dark grey areas represent the fibro-fatty tissues of the adventitia, the layer that is external to the sleeves. White areas among pale grey areas represent gaps in the venous wall that were without the outer myocardial sleeve. LI, left inferior pulmonary vein; LS, left superior pulmonary vein; RI, right inferior pulmonary vein; RS, right superior pulmonary vein.

Figure 3

Transverse sections through three sets of left pulmonary veins (LPV) showing the variations in circumferential arrangement of the myocardial sleeves. Myocardium is shown as dark grey and the venous wall is shown as pale grey. Note the myocardial sleeve completely surrounding the superior vein and extending beyond 10 mm from the venoatrial junction in the 38 year old patient. In contrast, there is incomplete encirclement of the sleeves in the 30 year old and 62 year old patients. The inferior veins have less extensive sleeves. 2 mm, 3 mm, 5 mm, 10 mm are the distances of the sections from the venoatrial junction (V-A). Trichrome stain.

Figure 4

Transverse sections showing variations in widths of the muscular isthmus between superior and inferior veins at the venoatrial junction in four hearts. The myocardial sleeves (dark grey) are a complex arrangement of circular and longitudinal bundles of myocytes. The myocardial sleeves in (A) show extensive fibrotic replacement (pale grey; small arrows) compared with another case of the same age shown in (B). The isthmus is narrow in (C) and fibrotic changes are insignificant. The case shown in (D) and (E) has hardly any sleeves. The left veins share an orifice. LPV, left pulmonary veins; RPV, right pulmonary veins. Trichrome stain.

Figure 5

(A) and (B) are longitudinal sections of the myocardial sleeve of the right superior pulmonary vein from a 47 year old man. (A) Degenerative changes with fibrous replacement. (B) Circularly arranged myocytes occupy nearly the full thickness. A fascicle of longitudinally arranged myocytes (double arrows) arises from the circularly arranged myocytes (star) as a separate bundle surrounded by fibrous tissue and fat. The bundle terminates within circularly oriented myocytes when followed distally (not shown). (C) is an enlargement of the isthmus between superior and inferior veins shown in fig 4B. The white arrows indicate the crossover of muscle bundles linking superior and inferior veins. There are abundant nerve bundles (thin arrows) in the vicinity. Trichrome stain. Epi and Endo mark the orientations for epicardial and endothelial surfaces, respectively, for panel (B).