Regional and Epi- to Endocardial Differences in Transmural Angles of Left Ventricular Cardiomyocytes Measured in Ex Vivo Pig Hearts: Functional Implications

Recent studies point toward the existence of a significant population of cardiomyocytes that intrude transmurally, in addition to those aligned tangentially. Our aim was to investigate the extent of transmural angulation in the porcine left ventricle using diffusion tensor magnetic resonance imaging (DTMRI). Hearts from eight 15 kg pigs were arrested in diastole. The ventricles were filled with polymer to maintain the end-diastolic dimensions. All hearts were examined using DTMRI to assess the distribution of transmural angulation of the cardiomyocytes at 12 predetermined locations covering the entirety of the left ventricle. We found significant differences between the regions, as well as within the transmural subcomponents. In eight out of the 12 predetermined mural segments, the highest mean transmural angle was located sub-endocardially. The greatest mean transmural angles were found in the anterior basal region, specifically 14.9 +/- 6.0-degree angle, with the greatest absolute value being 34.3-degree angle. This is the first study to show the significant heterogeneities in the distribution of helical and transmural angles within the entirety of the left ventricular walls, not only for different depths within the ventricular walls, but also between different ventricular regions. The results show unequivocally that not all the contractile elements are aligned exclusively in tangential fashion within the left ventricle. The main function of the transmurally intruding component is most likely to equalize and normalize shortening of the cardiomyocytes at all depths within the myocardium, but our findings also support the notion of antagonistic forces existing within the myocardial walls. Anat Rec, 296:1724-1734, 2013. (c) 2013 Wiley Periodicals, Inc.