Phase-plane analysis of left ventricular chamber filling and midwall fiber lengthening in patients with left ventricular hypertrophy.

Echocardiographic measurements of the left ventricle were used to define rates of circumferential fiber lengthening at the endocardium and midwall in 12 normal subjects and six patients with concentric left ventricular hypertrophy (wall thickness 11 to 16 mm). There was no difference in chamber size and systolic shortening in the two groups, but peak normalized lengthening rate [endocardial (+) VCF] was less than normal in the group with hypertrophy (4.8 +/- 1.4 and 3.1 +/- 0.9 sec-1, respectively, p less than .05). These results were contrasted with midwall (+) VCF data derived from two models that take into account nonuniform thickening across the left ventricular wall. Both models assume a constant left ventricular mass. The first allows changes in long axis and muscle cross-sectional area; the second assumes a constant cross-sectional area. Peak midwall (+) VCF with the first model was 2.1 +/- 0.5 sec-1 in the normal group and 1.4 +/- 0.3 sec-1 in the group with hypertrophy (p less than .01); with the second model peak midwall VCF was 2.8 +/- 0.6 and 1.4 +/- 0.4 sec-1 (p less than .01) in the two groups. The time to peak VCF and the dimension at the instant of peak (+) VCF were similar in the two groups. Phase-plane plots of length and velocity (dimension vs dD/dt) allow visual inspection and quantification of the relationships between instantaneous dimension, rate of change of dimension, and time in normal and hypertrophic hearts. These plots indicate abnormal filling of the left ventricular chamber and lengthening of midwall fibers in left ventricular hypertrophy.