Isovolumic Acceleration at Rest and During Exercise in Children: Normal Values for the Left Ventricle and First Noninvasive Demonstration of Exercise-Induced Force-Frequency Relationships

Objectives This study aimed to determine the normal variation of left ventricular (LV) isovolumic acceleration (IVA) in healthy children and to assess the feasibility of an entirely noninvasive method for demonstration of the LV force-frequency relationship (FFR). Background Pediatric cardiologists continue to seek noninvasive, load-independent indexes for the assessment of LV contractility and myocardial reserve. Methods Resting LV IVA was measured by echocardiogram in 236 healthy children and compared with their clinical characteristics. Further measurements were made in 51 children at incremental heart rates during semi-recumbent exercise. For these, FFRs were constructed by plotting LV IVA against heart rate. To assess potential clinical applications, pilot FFR data were collected from 16 children previously treated with anthracyclines. Results In healthy children, median resting LV IVA was 1.2 m/s 2 , interquartile range 0.9 to 1.6 m/s 2 . Resting LV IVA was unaffected by age, sex, weight, height, and body surface area but associated with baseline heart rate (r = 0.18, p = 0.0006). Noninvasive evaluation of the LV FFR was possible in 98% of subjects. Positive FFRs were confirmed in all the healthy children. By comparison, several of the children with anthracycline exposure demonstrated flattened force-frequency curves that were largely independent of resting LV ejection fraction and suggest reduced contractile reserve. Conclusions In children over 7 years, it is possible to demonstrate the LV FFR by interval measurement of IVA during exercise. The availability of pediatric normal values for both this relation and resting LV IVA might facilitate future investigation of LV contractility and myocardial contractile reserve during childhood.