An engineering analysis of myocardial fiber orientation in pig's left ventricle in systole

Abstract

The concept of discrete layers and bundles of muscle as a basic structural arrangement in left ventricular myocardium was tested by measuring the helix angles at 1 m m intervals from endocardium to epicardium, using pig's heart in the contracted state. A fixed coordinate system was established which permitted measurement of corresponding sites in hearts of different dimensions.The helix angle was found to change from somewhat less than 90" endocardially to about -90" epicardially in a n almost linear clockwise sequence, like a Japanese fan opened up. Approximately the same pattern was observed in the interventricular septum and the anterior, left and posterior walls. Generally, there was no abrupt change between the helix angle of papillary fibers and that of adjacent wall myocardium. Where occasionally abrupt changes in fiber orientation were demonstrated, no intervening septum could be discerned. The deviant fibers seemed to co-exist as part of the same gross structure.The concept of a continuum more appropriately describes the basic structure of left ventricular myocardium. Lev and Simkins ('56) and Grant ('65) showed that there was no evidence of identifiable layers as defined by the presence of connective tissue septa. This study shows no evidence of identifiable layers as defined by (1) a n abrupt change in fiber direction demarking the boundary of a layer and (2) a parallel fiber direction between such boundaries.For the past five centuries, prominent anatomists have been asserting that the ventricles are made up of discrete, overlapping muscle bands, each band being consistently identifiable. The history of this account of heart morphology beginning with Vesalius in 1514 has been reviewed by Robb and Robb ('42). In this view, myocardial structure is generally visualized like the layers of an onion, each layer of muscle fiber separated by wellmarked septa and having its own characteristic fiber direction. The standard unwinding technique for unraveling muscle bundles lends support to this idea.Recently Grant ('65) challenged the use of the unwinding technique. In this procedure, as employed by such anatomists as Mall ('ll), Shaner ('23) or Thomas ('57), a decollagenized muscle bundle is split off from the main muscle mass along a "natural" cleavage plane. However, myocardium is a syncytium with branch points. If there were no septa, one fiber would be ruptured when the cleavage plane reaches a point of fiber branching. Lev and Simkins ('56), reemphasized by Grant ('65), found that in unwinding the outer myo-ANAT. REC.. 155: 503-512.cardial fiber bundles, the choice of fiber to be ruptured depends upon the way the bundle is split off. Different populations of unwound fibers exposed different helix angles. The so-called "discrete" muscle bands do not have discrete "natural" cleavage planes between bundles. Rather, he observed, the helix angles in myocardial layers are continuous with each other and have a gradual transition from epicardium to endocardium. This modifies the old model of distinct la...

Normal Right Ventricular Three‐Dimensional Architecture, as Assessed with Diffusion Tensor Magnetic Resonance Imaging, is Preserved During Experimentally Induced Right Ventricular Hypertrophy

“…Thus, we used diffusion tensor magnetic resonance imaging to trace the primary diffusion vectors of the myocardium so as quantitatively to assess the overall orientation of the myocytes within different regions of the ventricular walls. We found the helical angle to change at different depths within the walls as established for the left ventricle, and as previously shown with histological techniques (Greenbaum et al, 1981), with endocardial myocytes aggregated so as to form right hand helical patterns, and epicardial myocytes aggregated as left hand helixes (Pettigrew, 1864;Streeter et al, 1966;Streeter et al, 1969;Schmid et al, 2005). Significantly, we were able to identify virtually identical myocardial tracks in hearts with or without hypertrophy, showing that the right ventricular wall is arranged in reproducible composites of aggregated myocytes, as has also been observed in the left ventricle (Smerup et al, 2008).…”

“…with as low a radius of curvature as possible (Krehl L, 1891). Although the measured helical angles of the aggregated right ventricle myocytes are similar to those found in the walls of the left ventricle (Streeter et al, 1966;Streeter et al, 1969), this is because we measured these angles relative to the long axis of the left ventricle, choosing this axis because of its consistent geometry between hearts when compared to the more complex right ventricular geometry. In this light, it is of interest to study the situations in which the right ventricle faces an increase in afterload so as to assess whether the fundamental morphological differences allow adaptation.…”

“…The overall scheme of left-handed helical patterns in the epicardial regions of the left ventricular walls, and reciprocal right-handed helical patterns in the endocardial regions, have been known since the stellar study of Pettigrew (Pettigrew, 1864). This architectural outline was revived by Streeter using histology (Streeter et al, 1966;Streeter et al, 1969), and has recently been fully consolidated using the technique of diffusion tensor magnetic resonance imaging (Helm et al, 2005;Rohmer et al, 2007). Using this novel, but validated, technique (Hsu et al, 1998;Scollan et al, 1998), we have now demonstrated that in keeping with the demonstration of myocytes also aggregated in transmural fashion (Lunkenheimer et al, 2006), reproducible pathways can be demonstrated within the walls using diffusion tensor magnetic resonance imaging (Smerup et al, 2008).…”

Myocardial Matrix Remodeling and the Matrix Metalloproteinases: Influence on Cardiac Form and Function

“…The architectural complexity of the myocardium and the potential role that the ECM played in maintaining unique myocyte orientations throughout the LV free wall were described by Streeter and Basset (417,418). Using a structural engineering approach, these authors demonstrated that myocyte orientation and myocardial fiber angles were highly organized and moved in a continuous fashion from the endocardium to the epicardium.…”

Simulating cardiac ultrasound image based on MR diffusion tensor imaging

“…These anisotropies are derived from the variable distributions of cardiac fiber orientations. 39,40 This method utilized the DTI-based fiber orientations to simulate the anisotropic effects by processing the point scatterers with an ellipsoidal filter. Although different angles between fiber orientations and ultrasound beam directions lead to different intensities, the proposed simulation method can model these differences of myocardial intensities as the real imaging does.…”