Myocardial fiber diameter and regional distribution in the ventricular wall of normal adult hearts, hypertensive hearts and hearts with hypertrophic cardiomyopathy.

Myocardial fiber diameters were measured to determine their distribution throughout the ventricular wall in normal adult hearts, hypertensive hearts and hearts with hypertrophic cardiomyopathy (HCM). In normal adult hearts and hypertensive hearts, the diameter decreased from the inner to the outer third of the left ventricular free wall and from the left ventricular side to the right ventricular side of the septum. In HCM, these regional differences were preserved in the left ventricular free wall, but not in the septum. The diameter was greatest in the middle third of the septum, where myocardial fiber disarray was widely distributed. The diameters of the fibers in the right ventricular side of the septum were significantly larger than those of the fibers in the left ventricular side of the septum in HCM. This finding, in contrast to that in normal adult hearts or hypertensive hearts, was considered to be related to the inward convex curvature of the left ventricular chamber. Although there was no significant difference in the diameter of myocardial fibers in the left ventricular free wall between hypertensive hearts and hearts with HCM, the diameters of those in the right ventricular free wall, in the right ventricular side of the septum and in the middle third of the septum were significantly larger in HCM than in hypertensive hearts. We conclude that there is a transmural variation of myocardial fiber diameter in the left ventricular free wall and the ventricular septum, and such transmural variation in HCM is clearly different from that in hypertensive hearts.