Published online before print December 23, 2004, doi: 10.1161/01.RES.0000153979.71859.e7
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Submitted on July 8, 2004
Revised on November 9, 2004
Accepted on December 10, 2004
Epicardial Fiber Organization in Swine Right Ventricle and Its Impact on Propagation
Frederick J. Vetter ;
From the Biomedical Engineering Program (F.J.V.), Department of Electrical and Computer Engineering, University of Rhode Island, Kingston; and Department of Pharmacology (S.B.S., S.M., C.J.H., A.M.P.), SUNY Upstate Medical University, Syracuse, NY.
* To whom correspondence should be addressed. E-mail: pertsova{at}upstate.edu.
Fiber organization is important for myocardial excitation and contraction. It can be a major factor in arrhythmogenesis and current distribution during defibrillation shocks. In this study, we report the discovery of a previously undetected thin epicardial layer in swine right ventricle (RV) with distinctly different fiber orientation, which significantly affects epicardial propagation. Experiments were conducted in isolated coronary-perfused right ventricular free wall preparations (n=8) stained with the voltage-sensitive dye di-4-ANEPPS. Optical signals were recorded from the epicardium with a CCD video camera at 800 fps. Preparations were sectioned parallel to the epicardial surface with a resolution of 50 µm or better. To link the histological data with the observed activation patterns, resulting fiber angles were introduced into a 3D computer model to simulate the electrical activation and voltage-dependent optical signals. In all preparations, we detected a thin epicardial layer with almost no depth-dependent fiber rotation. The thickness of this layer (z0) varied from 110 to 930 µm. At the boundary of this layer, we observed an abrupt change in fiber angle by 64±13° followed by a gradual fiber rotation in the underlying layers. In preparations with z0 <700 µm, optical mapping during epicardial stimulation revealed unusual diamond- and rectangular-shaped activation fronts with two axes of fast conduction. Computer simulations accurately predicted the features of the experimentally recorded activation fronts. The free wall of swine RV has a thin epicardial layer with distinctly different fiber orientation, which can significantly affect propagation and give rise to unusually shaped activation fronts. This is important for understanding electrical propagation in the heart, and further refines the existing knowledge of myocardial fiber architecture.
Key words: myofiber organization • optical mapping • propagation
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