Extracellular mapping of canine pulmonary veins revealed slow and complex conduction with activation delays up to 96 ms over 3 mm, correlating with abrupt changes in myocardial fiber orientation.
The complex architecture of muscular sleeves in canine pulmonary veins causes zones of activation delay, which may facilitate reentry and arrhythmias associated with ectopic activity.
Background — Paroxysmal atrial fibrillation in patients is often initiated by foci in the pulmonary veins. The mechanism of these initiating arrhythmias is unknown. The aim of this study was to determine electrophysiological characteristics of canine pulmonary veins that may predispose to initiating arrhythmias. Methods and Results — Extracellular recordings were obtained from the luminal side of 9 pulmonary veins in 6 Langendorff-perfused dog hearts after the veins were incised from the severed end to the ostium. Pulmonary veins were paced at the distal end, the ostium, and an intermediate site. During basic and premature stimulation, extracellular electrical activity was recorded with a grid electrode that harbored 247 electrode terminals. In 4 hearts, intracellular electrograms were recorded with microelectrodes. Myocyte arrangement immediately beneath the venous walls was determined by histological analysis in 3 hearts. Extracellular mapping revealed slow and complex conduction in all pulmonary veins. Activation delay after premature stimulation could be as long as 96 ms over a distance of 3 mm. Action potential duration was shorter at the distal end of the veins than at the orifice. No evidence for automaticity or triggered activity was found. Histological investigation revealed complex arrangements of myocardial fibers that often showed abrupt changes in fiber direction and short fibers arranged in mixed direction. Conclusions — Zones of activation delay were observed in canine pulmonary veins and correlated with abrupt changes in fascicle orientation. This architecture of muscular sleeves in the pulmonary veins may facilitate reentry and arrhythmias associated with ectopic activity.
Hocini et al. (Tue,) conducted a other in Paroxysmal atrial fibrillation (n=6). Electrophysiological mapping and histological analysis was evaluated on Electrophysiological characteristics and myocyte arrangement of pulmonary veins. Extracellular mapping of canine pulmonary veins revealed slow and complex conduction with activation delays up to 96 ms over 3 mm, correlating with abrupt changes in myocardial fiber orientation.