NONINVASIVE MEASUREMENT OF SHORTENING IN THE FIBER AND CROSS-FIBER DIRECTIONS IN THE NORMAL HUMAN LEFT-VENTRICLE AND IN IDIOPATHIC DILATED CARDIOMYOPATHY

Background Studies in anesthetized dogs have shown that myocardial fib ers shorten approximate to 8%. However, in the endocardium, shortening occurs to a much greater extent at 90 degrees to the fiber orientatio n (''cross-fiber shortening'') than it does along the fiber direction. The purpose of this study was to estimate the extent of fiber and cro ss-fiber shortening in the normal human left ventricle and in patients with idiopathic dilated cardiomyopathy (IDC). Methods and Results Ten normal subjects and nine patient with IDC were imaged with magnetic r esonance tissue tagging. Finite strain analysis was used to calculate endocardial and epicardial shortening in the fiber and cross-fiber dir ections using anatomic fiber angles from representative autopsy specim ens as references. Anatomic fiber angles were not different between no rmal subjects and IDC patients. Epicardial fiber strain was -0.14+/-0. 01 in normal subjects and -0.08+/-0.01 in IDC patients (P<.0001 versus normal subjects). Epicardial cross-fiber strain was -0.08+/-0.01 in n ormal subjects and -0.06+/-0.01 in IDC patients (P=NS). Endocardial fi ber strain was -0.16+/-0.01 in normal subjects and -0.09+/-0.01 in IDC patients (P<.0001), and endocardial cross-fiber strain was -0.26+/-0. 01 in normal subjects and -0.15+/-0.01 in IDC pa tients (P<.0001). Cro ss-fiber shortening was greater than fiber shortening al the endocardi um in both normal subjects (P<.0001) and IDC patients (P<.05). Conclus ions In normal humans, the direction of maximal deformation aligns wit h the fiber direction in the epicardium but is perpendicular to the fi ber direction in the endocardium. When strain in a coordinate system a ligned to the fibers is estimated, cross-fiber shortening is found to be the dominant shortening strain at the endocardium. Normal fiber sho rtening is approximate to 15%, and this is markedly reduced in IDC. Th e normal transition in fiber orientation through the wall is not alter ed in IDC, and cross-fiber shortening is still the dominant strain at the endocardium, suggesting that interactions between myocardial layer s persist in these patients.