Fiber orientation in hypertrophied canine left ventricle

Abstract

Myocardial fiber orientation was examined in transmural specimens from the maximum diameter of the left ventricle from 5 dogs with pressure-overload hypertrophy produced by aortic stenosis, 6 dogs with volume-overload hypertrophy due to an arteriovenous fistula and 6 exercise-hypertrophied dogs. Hearts arrested in diastole were fixed in situ while operating end-diastolic pressure was maintained. Fiber orientation changed smoothly from about +60.degree. (with respect to the equator) at the endocardium to about -69.degree. at the epicardium. Most fibers near the midwall were oriented circumferentially. These findings are similar to those reported for normal dogs. Compared to normals, the left ventricles from dogs with pressure-overload had an increase in longitudinally oriented fibers, i.e., fiber angles between -67.5.degree. and -90.degree. and between +67.5.degree. and +90.degree.; these fibers comprised 10.4 .+-. 1.8% of the total fibers in dogs with aortic stenosis vs. 2.9 .+-. 1.8% of total fibers in normal dogs (P < 0.001). The dogs with volume-overload hypertrophy or exercise-trained animals were not significantly different from normals.