Mean Velocity of Fiber Shortening

Abstract

Previously it was shown that left ventricular (LV) myocardial contractility can be assessed from the instantaneous relation between velocity of fiber shortening and maximum LV wall tension (V_CF at max T). Such analysis is complex, requiring frame-by-frame correlation of LV dimensions with pressure, and a simpler approach was sought. In 50 patients the mean velocity of circumferential fiber shortening (mean V_CF), determined from the systolic excursion of the LV internal minor equator obtained by cineangiography, was compared with instantaneous tension-velocity relations. In 13 subjects without LV disease, V_CF at max T averaged 1.74 ± 0.31 (mean ± sd) circumferences (circ)/sec (range, 1.37-2.52); corresponding mean V_CF was 1.50 ± 0.27 circ/sec (range, 1.23-2.03). In 22 patients with LV myocardial disease V_CF at max T averaged 0.64 ± 0.29 circ/sec (range, 0.12-1.27); mean V_CF averaged 0.68 ± 0.36 circ/sec (range, 0.15-1.29, P < 0.001 compared with normal subjects). Similar results were obtained in 15 patients with valvular lesions and an abnormal V_CF at max T. Mean V_CF detected impaired myocardial function in 95% of patients with abnormal instantaneous tension-velocity relations, and in the remaining 5% the amount of overlap between normal and abnormal mean V_CF was slight. The extent of fiber shortening and the percent shortening of the internal diameter at the minor equator did not provide separation of normal from abnormal groups. It is concluded that the mean velocity of fiber shortening provides a simplified method of estimating LV contractility which: (1) requires analysis of only two frames of a cineangiogram; (2) allows quantitative comparison of LV myocardial contractility among patients; (3) adequately detects altered cardiac performance, even when valvular disease and myocardial dysfunction coexist.