Determination of left ventricular diastolic chamber stiffness and myocardial stiffness in patients with congenital heart disease.

Left ventricular diastolic indexes were derived in 13 patients aged 5 to 21 years. Three had a normal heart, three had lesions causing volume overload and seven had coarctation of the aorta, including one whose main lesion was severe endocardial fibroelastosis. At cardiac catheterization simultaneous high fidelity pressure (P) and left ventricular volume (V) measurements were obtained and several points in one diastolic cycle taken. With use of a monoexponential formula (P = aebv) for P versus V, dP/dv and the operant chamber stiffness b were obtained. Similarly, with use of sigma = alpha e beta epsilon, d sigma/d epsilon, elastic stiffness (E) and the muscle stiffness constant KE were obtained. Values for b were 0.0273 +/- 0.0065 in normal subjects, 0.017 +/- 0.0043 in those with volume overload, 0.0369 +/- 0.0173 in those with coarctation (without endocardial fibroelastosis) and 0.0192 in the child with endocardial fibroelastosis. The plot of P versus V for coarctation was to the left and steeper than normal and the patients with volume overload had a flattened rightward curve, whereas the curve for those with endocardial fibroelastosis was extremely rightward. The stress-radii curves of the normal subjects and those with coarctation were similar whereas the curves for patients with volume overload and endocardial fibroelastosis were rightward of normal. The value for KE was 8.92 +/- 0.87 for the normal subjects, 8.26 +/- 0.75 for those with volume overload, 9.2 +/- 2.5 for those with coarctation and 22.75 for those with endocardial fibroelastosis. Thus, the pressure-loaded ventricle is stiffer than the normal, which in turn, is stiffer than the volume-loaded ventricle. This response, due to hypertrophy, appears to be appropriate in that diastolic stress was normalized and muscle stiffness was not increased except in the patient with endocardial fibroelastosis.