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EXPERIMENTAL STUDIES

Effect of myocardial hypertrophy on systolic and diastolic function in children: insights from the force-frequency and relaxation-frequency relationships

^a Division of Cardiology, Children’s Hospital Medical Center, Cincinnati, Ohio, USA

Manuscript received January 28, 1998; revised manuscript received May 22, 1998, accepted June 2, 1998.

Address for correspondence: Anirban Banerjee, MD, Director of Pediatric Echoradiography, Floating Hospital for Children, NEMC #313, 750 Washington St., Boston, Massachusetts 02111

Objective. The objective of this study was to evaluate the effect of myocardial hypertrophy on systolic and diastolic properties of the left ventricle in children.

Background. In children with myocardial hypertrophy, ejection phase indices are invariably increased. However, indices of force-generation, e.g., end-systolic elastance and invasive indices of diastolic properties, have been studied infrequently in children with myocardial hypertrophy.

Methods. We studied 10 children with congenital aortic stenosis or coarctation of aorta and nine control patients. 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 110 to 160 beats per minute. Diastolic properties were assessed from time constant of relaxation () at matched heart rates, chamber stiffness constant, myocardial stiffness constant, and relaxation-frequency relationship measured at gradually increasing heart rates.

Results. E_fes remained unchanged by myocardial hypertrophy, however, was prolonged (_L: 27.3 ± 2.3 vs. 21.8 ± 2.2 ms, p < 0.001; and _D: 43.2 ± 3.1 vs. 34.3 ± 3.3 ms, p < 0.001). Both chamber and myocardial stiffness constants remained unchanged. Incremental increases in heart rate produced incremental improvement in both contraction and relaxation. Slopes of force-frequency and relaxation-frequency relationships remained unchanged in the experimental group. However, the relaxation-frequency relationship manifested a parallel shift upward.

Conclusions. In conscious, sedated children with myocardial hypertrophy, systolic function assessed by an index of force generation remains unchanged. However, relaxation is prolonged but passive diastolic properties remain unaffected. The combined effect of hypertrophy and heart rate does not alter the force-frequency and relaxation-frequency relationships.

Abbreviations and Acronyms   Efes = end-systolic fiber elastance   L = time constant of relaxation (zero asymptote method)   D = time constant of relaxation (variable asymptote method)   kc = chamber stiffness constant   km = myocardial stiffness constant   LV = left ventricular

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