Epicardial Fiber Organization in Swine Right Ventricle and Its Impact on Propagation

Abstract

Abstract-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 (nϭ8) 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 m 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 (z 0 ) varied from 110 to 930 m. At the boundary of this layer, we observed an abrupt change in fiber angle by 64Ϯ13°followed by a gradual fiber rotation in the underlying layers. In preparations with z 0 Ͻ700 m, 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 Ⅲ optical mapping Ⅲ propagation T he fiber organization of ventricular myocardium is a significant determinant of both its mechanical function and its electrical propagation [1][2][3] Myocardial fiber organization has been implicated in the mechanisms of ventricular arrhythmias as one of the important factors responsible for the stability of 3D reentrant activity. 4 -8 It is also thought to affect current distribution during defibrillation shocks 9,10 and thus affect their odds of failure and success. All this explains the persistent interest in structural aspects of myocardial organization 11,12 and motivates further refining the existing knowledge of myocardial fiber architecture.The characteristic feature of myocardial fiber organization is the gradual counterclockwise rotation of fibers throughout the heart wall 1,13-16 with the total rotation angle from endocardium to epicardium across species ranging from 120°( dog) to 180°(pig). 17,18 Although in general the dependence of fiber rotation on depth is considered well established, information about fiber organization near the epicardial surface remains scarce.There are in...

Heart structural remodeling in a mouse model of Duchenne cardiomyopathy revealed using optical polarization tractography [Invited]

“…An iterative Jones calculus based algorithm was applied to extract the depth-resolved optic axis for mapping the fiber orientation [13]. The fiber orientation measured is between [-90°, 90°] and represents the projected orientations within the plane perpendicular to the incident light [8,14], which is analog to the "helix" angle measured in DTI [2,7]. The system has a 12.4 µm lateral resolution at the focus and a 5.9 µm axial resolution in tissue.…”

“…However, in addition to its high system cost, the limited spatial resolution of DTI makes it extremely challenging for revealing detailed myocardial fiber structure in the small mouse hearts. A typical mouse heart has a diameter of ~6 mm with 1~2 mm thick ventricular wall and the myofiber orientation can change over 100° across the thin ventricular wall [6,7]. Abrupt orientation changes of more than 50° were observed between different epicardial layers [7].…”

“…A typical mouse heart has a diameter of ~6 mm with 1~2 mm thick ventricular wall and the myofiber orientation can change over 100° across the thin ventricular wall [6,7]. Abrupt orientation changes of more than 50° were observed between different epicardial layers [7]. Therefore, a sufficient resolution is important for correctly imaging detailed fiber orientation changes in the ventricular wall of the heart.…”

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“…It was also shown that the morphology of optical AP changes with the change in the direction of the wave front propagation, because of the complex anisotropy of the myocardium [19]. However, in their study, the authors obtained the fiber orientations (on a 3D slab of tissue) via histology.…”