In canine models, an abrupt increase in muscle thickness between the PV and LA (0.42 vs 2.0 mm, P<0.01) and complex fiber orientations provided an anatomical basis for conduction disturbances.
BACKGROUND: The roles of complex muscle sleeve geometry and fiber orientation in the pulmonary veins (PVs) in wave-front propagation are poorly understood. METHODS AND RESULTS: We mapped the left superior PV (LSPV, n=7) and left inferior PV (LIPV, n=4) of dogs with 420 bipolar electrodes (1-mm resolution) and performed detailed histological examination. In the anterior LSPV-left atrial (LA) junction, myocardial muscle fibers were oriented perpendicular to PV blood flow. A wedge filled with connective tissues led to a complete muscle separation or an abrupt increase in muscle thickness between the PV and LA (0.42+/-0.12 versus 2.0+/-0.31 mm, P<0.01). Distal LSPV pacing resulted in conduction block at the anterior PV-LA junction, with double potentials. In contrast, the posterior LSPV-LA junction showed gradual muscle thickening and a fiber orientation parallel to the blood flow. The maximum PV muscle thickness in the anterior PV-LA junction is thinner than that in the posterior junction (0.83+/-0.15 versus 1.3+/-0.38 mm, P<0.01). Distal LIPV pacing showed multiple PV-LA breakthroughs, with segmental conduction block in the anterior PV-LA junction. The conduction block corresponded to segmental PV-LA muscle disconnection. Complex fiber orientations in the PV muscle sleeves away from the PV-LA junction were responsible for intra-PV conduction delay or block during rapid PV pacing. CONCLUSIONS: We conclude that segmental muscle disconnection and differential muscle narrowing at PV-LA junctions and complex fiber orientations within the PV provide robust anatomical bases for conduction disturbance at the PV-LA junction and complex intra-PV conduction patterns.
Hamabe et al. (Mon,) conducted a other in Canine pulmonary vein anatomy and electrical activation (n=11). High-resolution mapping and histological examination was evaluated on Correlation between anatomy (muscle thickness, fiber orientation) and electrical activation. In canine models, an abrupt increase in muscle thickness between the PV and LA (0.42 vs 2.0 mm, P<0.01) and complex fiber orientations provided an anatomical basis for conduction disturbances.