Statistical Analysis of the Angle of Intrusion of Porcine Ventricular Myocytes from Epicardium to Endocardium Using Diffusion Tensor Magnetic Resonance Imaging

Abstract

Pairs of cylindrical knives were used to punch semicircular slices from the left basal, sub-basal, equatorial, and apical ventricular wall of porcine hearts. The sections extended from the epicardium to the endocardium. Their semicircular shape compensated for the depth-related changing orientation of the myocytes relative to the equatorial plane. The slices were analyzed by diffusion tensor magnetic resonance imaging. The primary eigenvector of the diffusion tensor was determined in each pixel to calculate the number and angle of intrusion of the long axis of the aggregated myocytes relative to the epicardial surface. Arrays of axially sectioned aggregates were found in which 53% of the approximately two million segments evaluated intruded up to 6158, 40% exhibited an angle of intrusion between 6158 and 6458, and 7% exceeded an angle of 6458, the positive sign thereby denoting an epi-to endocardial spiral in clockwise direction seen from the apex, while a negative sign denotes an anticlockwise spiral from the epicardium to the endocardium. In the basal and apical slices, the greater number of segments intruded in positive direction, while in the sub-basal and equatorial slices, negative angles of intrusion prevailed. The sampling of the primary eigenvectors was insensitive to postmortem decomposition of the tissue. In a previous histological study, we also documented the presence of large numbers of myocytes aggregated with their long axis intruding obliquely from the epicardial to the endocardial ventricular surfaces. We used magnetic resonance diffusion tensor imaging in this study to provide a comprehensive statistical analysis.

Determinants of left ventricular shear strain

“…It is this distribution of ␣ t that was used in the FIB simulation. Meanwhile, more recent experimental investigations have confirmed the earlier observations by Streeter and colleagues that myofiber orientation in the LV wall has a component in transmural direction (1,13,18,23,24,25,32). Accurate quantification of ␣ t has proven to be difficult, among others, because the unique definition of a wall-bound coordinate system to which the fiber orientation can be referred to is difficult (13).…”

“…Accurate quantification of ␣ t has proven to be difficult, among others, because the unique definition of a wall-bound coordinate system to which the fiber orientation can be referred to is difficult (13). Yet, the main experimental findings are that ␣ t is positive in the basal part and negative in the apical part of the LV wall (13,18,32), that ␣ t reaches its extremum closer to the endocardial surface than the epicardial surface (24), and that ␣ t is small (Ͻ5°) in the bulk of the myocardium but certainly not small near the apex and base (23), with some studies (25,32) reporting that the magnitude of ␣ t may increase up to 40°. The distribution of ␣ t in the FIB simulation agrees with these experimental findings.…”

The three‐dimensional arrangement of the myocytes in the ventricular walls

“…7). As already stated, when we used circular knives to compensate for the changing helical angle of the long axis of the aggregated myocytes (Lunkenheimer et al, 2006;Schmid et al, 2007), we found that the orientation of significant numbers of myocytes deviated by values up to 408 from the anticipated tangential alignment, with variations in both positive and negative directions. Our ongoing studies, therefore, add still further evidence to our view that the ventricular myocardium is a three-dimensional meshwork of myocytes set in a supporting matrix of fibrous tissue.…”

“…According to our previous observations, nonetheless, about one-third of the myocytes aggregated within the walls of the left ventricle are aligned at various angles from the epicardium toward the endocardium, with some achieving angulations of up to 408 (Lunkenheimer et al, 2006;Schmid et al, 2007). By virtue of the parallelogram of forces, these myocytes are able, with one vector, to sustain tangential ventricular constriction, while with a smaller vector, they oppose systolic mural thickening.…”

“…This problem can be circumvented by sectioning blocks removed from the ventricular walls using circular knives, the turn of the circular blade compensating for the change in helical angle. These studies (Lunkenheimer et al, 2006;Schmid et al, 2007) have shown that a significant population of myocytes traverses the ventricular walls at angles of up to 408. The anatomic evidence, therefore, in our opinion, shows that the walls of the heart are arranged in the form of a modified blood vessel, with the myocytes aggregated together as a three-dimensional meshwork supported by a matrix of fibrous tissue.…”