EFFECT OF MYOCARDIAL HYPERTROPHY ON SYSTOLIC AND DIASTOLIC FUNCTION IN CHILDREN - INSIGHTS FROM THE FORCE-FREQUENCY AND RELAXATION-FREQUENCY RELATIONSHIPS

Objective. The objective of this study was to evaluate the effect of m yocardial hypertrophy on systolic and diastolic properties of the left ventricle in children. Background. In children with myocardial hypert rophy, ejection phase indices are invariably increased. However, indic es of force-generation, e.g., end-systolic elastance and invasive indi ces of diastolic properties, have been studied infrequently in childre n with myocardial hypertrophy. Methods. We studied 10 children with co ngenital aortic stenosis or coarctation of aorta and nine control pati ents. Systolic properties,were assessed from shortening fraction, end- systolic fiber elastance (E-fes) measured at resting heart rates, and force-frequency relationship measured at heart rates increasing from 1 10 to 160 beats per minute. Diastolic properties were assessed from ti me constant of relaxation (tau) at matched heart rates, chamber stiffn ess constant, myocardial stiffness constant, and relaxation-frequency relationship measured at gradually increasing heart rates. Results. E- fes remained unchanged by myocardial hypertrophy, however, tau was pro longed (tau(L): 27.3 +/- 2.3 vs. 21.8 +/- 2.2 ms, p < 0.001; and tau(D ): 43.2 +/- 3.1 vs. 34.3 +/- 3.3 ms, p < 0.001). Both chamber and myoc ardial stiffness constants remained unchanged. Incremental increases i n heart rate produced incremental improvement in both contraction and relaxation. Slopes of force frequency and relaxation-frequency relatio nships remained unchanged in the experimental group. However, the rela xation-frequency relationship manifested a parallel shift upward. Conc lusions. In conscious, sedated children with myocardial hypertrophy, s ystolic function assessed by an index of force generation remains unch anged. However, relaxation is prolonged but passive diastolic properti es remain unaffected. The combined effect of hypertrophy and heart rat e does not alter the force-frequency and relaxation-frequency relation ships. (C) 1998 by the American College of Cardiology.