Left ventricular chamber filling and midwall fiber lengthening in patients with left ventricular hypertrophy: Overestimation of fiber velocities by conventional midwall measurements

Abstract

Observations that the inner (subendocardial) half of the left ventricular wall contributes more to total left ventricular wall thickening than the outer (subepicardial) half may have important implications in the analysis of myocardial fiber length transients. Accordingly, we measured endocardial and midwall shortening and lengthening rates in normal and hypertrophic hearts and compared the results obtained with conventional methods of measurement with those obtained with a modified model that does not depend on use of conventional assumptions about the midwall. This modified (two-shell cylindrical model) method considers the substantial contribution of inner wall thickening and thus does not require the assumption of a theoretical midwall fiber that remains at the midwall throughout the cardiac cycle. Echocardiographic data from six normal subjects and six patients with concentric left ventricular hypertrophy (LVH) were examined; left ventricular wall thickness ranged from 8 to 10 mm in normal subjects and from 11 to 16 mm in the patients with LVH. By design, the standard measurements of left ventricular size (diastolic and systolic dimensions) and systolic function (fractional shortening and endocardial fiber shortening velocities) were equal in the two groups. Endocardial, conventional midwall, and modified midwall methods all indicate reduced fiber lengthening rates in patients with LVH; peak fiber lengthening rates for normal and LVH groups were 4.5 ± 0.7 vs 3.1 ± 0.8 sec-1 (p .02) at the endocardium, 2.3 ± 0.4 vs 1.6 ± 0.4 sec-1 (p < .02) at the midwall (conventional method), and 2.1 ± 0.3 vs 1.4 ± 0.3 sec-1 (p < .01) at the midwall (modified method). Chamber filling and fiber lengthening rates are depressed in patients with concentric LVH. Conventional measurements overestimate 'true' fiber velocities more in those with LVH than in normal subjects; thus, the modified midwall method offers a theoretical advantage, especially in studies in which data from normal and hypertrophic hearts are compared.