Effect of increased wall thickness on indices of left ventricular pump function in children.

OBJECTIVE: To investigate whether augmented chamber performance in children with a concentric hypertrophied left ventricle is due to increased myocardial shortening or a geometric effect of the thickened ventricular wall. DESIGN: Chamber performance in terms of fractional area change and myocardial shortening--that is, circumferential midwall shortening--were measured by cross sectional echocardiography in young people with normal left ventricles and those with concentric hypertrophy of the left ventricle. PATIENTS: 52 healthy infants, children, and young people (age range 3 1/2 weeks to 26 years; body weight 1.8-89 kg (mean 23.6 kg)) and 29 infants, children, and adolescents with ventricular hypertrophy (mean body weight 31.4 kg, age range 4 weeks to 18.7 years). MAIN OUTCOME MEASURES: Chamber areas, fractional area change, midwall circumferential shortening normalised to body weight. RESULTS: In the controls normalised reference values were: end diastolic cavity area, 1.47 (0.25) cm2/kg0.65; fractional area change, 0.56 (0.03); end diastolic myocardial area, 1.62 (0.25) cm2/kg0.55; midwall circumferential shortening, 0.21 (0.03). By comparison, the patients had normal chamber areas (end diastolic myocardial area, 1.57 (0.42) cm2/kg0.65), increased fractional area change, 0.68 (0.05) (P < 0.001), and normal midwall circumferential shortening, 0.21 (0.03). There was a significant relation between the degree of hypertrophy (in terms of end diastolic myocardial area) and pump function while midwall shortening remained constant: 0.08 x end diastolic myocardial area + 0.44 (r = 0.74, P < 0.001). CONCLUSIONS: The relation between myocardial shortening, wall thickness, and fractional area change emphasises that the augmentation of pump function variables in left ventricular hypertrophy in young people is an effect of the thickened wall and not necessarily due to increased myocardial shortening. This relation offers the possibility of assessing the adequacy of chamber performance with respect to the degree of hypertrophy.