Virtual sectioning of cardiac tissue relative to fiber orientation

Ventricular myocardium is composed of muscle fibers organised into a complex, branching, laminar (sheet-like) structure. The fibers run approximately parallel to the epicardial wall, but their orientation relative to the circumferential axis varies transmurally, rotating from around −70° at the epicardium to +70° at the endocardium. This ensures that any flat transmural imaging plane or histological section contains only a partial description of myocardial architecture, as fibers intersect with the image plane at a variety of angles depending on transmural depth. We have developed a new way of viewing microstructure that accounts for this variation. Extended-volume confocal 3-D images of normal rat left-ventricular wall have previously been acquired, with an approximate size of 4 × 1 ×1 mm³. The transmural fiber rotation is measured on planes parallel to the epicardium, and used to define a curvilinear coordinate system with a transmural axis, and a second axis defined relative to the local fiber orientation. Images extracted from the image volume on curvilinear planes derived from these axes reveal a consistent view of myocardial architecture.