Abstract 18262: Left Ventricle Strain Rate in Children Demonstrates Heart Rate Dependence and a Force-frequency Relationship

Abstract

Introduction: In adult pigs and human studies, strain rate (SR) is a valid and reproducible marker of contractility. It is also heart rate (HR) independent, hence lacks force-frequency relationship (FFR). Isovolumic acceleration (IVA) is a proven non-invasive load-independent measure of LV contractility used in research settings. This study sought to assess SR behavior during tachycardia and inotropic stimulation in children, compared to IVA. Methods: Twenty-four patients (median age, 13.9; range 7.8 - 22.5 years) with no structural or functional heart abnormalities were evaluated after a radiofrequency ablation procedure. Echocardiogram was performed at baseline, during atrial pacing and isoprenaline infusion to achieve 130% of baseline HR. Speckle tracking global LV longitudinal SR and tissue Doppler septal IVA were measured. Relationships between HR, SR and IVA were assessed. Percent (%) change and absolute differences between SR and IVA at baseline, pacing and isoprenaline were evaluated. Data are reported as median and interquartile ranges. Results: SR and IVA showed a moderate correlation with HR at baseline (SR: r=-0.68, p=0.0002; IVA: r=0.46, p=0.01), and during pacing (SR: r=-0.56, p=0.003; IVA: r=0.58, p=0.002). Both SR and IVA increased with pacing and isoprenaline (table 1), however the greatest % change was seen during isoprenaline infusion for IVA (p < 0.006) and SR (p < 0.0001). Conclusion: SR enhances with increasing HR in children, demonstrating a relative HR dependence and a FFR. This is contrary to findings in adult studies, thus this study highlights that children show a different LV mechanical response to chronotropic effects and therefore caution should be use when extrapolating of adult findings to children.