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

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 heart 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 less than .02) at the endocardium, 2.3 +/- 0.4 vs 1.6 +/- 0.4 sec-1 (p less than .02) at the midwall (conventional method), and 2.1 +/- 0.3 vs 1.4 +/- 0.3 sec-1 (p less than .01) at the midwall (modified method).(ABSTRACT TRUNCATED AT 250 WORDS)