Anatomy and myoarchitecture of the left ventricular wall in normal and in disease.

The normal left ventricle comprises an inlet, apical trabecular, and an outlet portion although these portions do not have discrete anatomical borders. The ventricular wall is thickest near the cardiac base and thins to 1-2 mm at the apex. Characteristically, the muscle bundles at the apical portion are thin, but there are also thicker bundles and very fine strands that may be mistaken on imaging as pathologies. Transmurally through the ventricular wall, the myoarchitecture has a typical arrangement of myocardial strands that change orientation from being oblique in the subepicardium to circumferential in the middle and to longitudinal in the subendocardium. The circumferential portion is the thickest with the longitudinal portion the thinnest. In the hypertrophied ventricle the circumferential portion is reduced. In combination with alterations in the quality and quantity of the connective tissue matrix, myoarchitecture impacts on myocardial function.