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Strain Rate in Children and Young Piglets Mirrors Changes in Contractility and Demonstrates a Force-Frequency
Silvia V Alvarez1, Etienne Fortin-Pellerin2, Mohammed Alhabdan3
1Division of Pediatric Cardiology, University of Alberta, Stollery Children's Hospital, Edmonton, Alberta, Canada.
Insights
Strain rate (SR) in children and piglets increases with heart rate and inotropic stimulation, demonstrating a force-frequency relationship. This finding suggests SR is a valid measure of myocardial contractility in the immature heart.
Area of Science:
- Pediatric Cardiology
- Cardiac Physiology
- Echocardiography
Background:
- Adult myocardial strain rate (SR) correlates with contractility but lacks a force-frequency relationship.
- Maturation significantly alters myocardial properties, making adult findings inapplicable to the immature heart.
- The force-frequency relationship is a fundamental characteristic of myocardial contraction.
Purpose of the Study:
- To evaluate the strain rate (SR) response in the immature heart to increased heart rate (HR) and inotropic stimulation.
- To determine if the immature heart exhibits a force-frequency relationship.
- To assess SR as a measure of contractility in pediatric and neonatal populations.
Main Methods:
- Part 1: Echocardiography in 23 children (7.8-17.5 years) measuring LV speckle tracking-derived SR and tissue Doppler IVA during atrial pacing and isoprenaline infusion.
- Part 2: Invasive assessment of LV dP/dt and speckle tracking-derived SR in young piglets (1-17 days) at varying heart rates (200, 230, 260 bpm).
- Statistical analysis using repeated measures ANOVA to compare with baseline values.
Main Results:
- In children, LV SR and IVA significantly increased with pacing and isoprenaline (P < .001).
- In piglets, SR and invasive dP/dt significantly increased with rising HR (P < .01 and P < .001).
- Both SR and dP/dt plateaued at the highest HRs in piglets, with a concurrent decrease in LV end-diastolic dimension.
Conclusions:
- Strain rate (SR) in children is augmented by chronotropic and inotropic stimulation.
- Young infant piglets' SR is augmented by chronotropic stimulation.
- Both children and piglets exhibit a force-frequency relationship for SR, supporting its role as a contractility measure in immature hearts.
Background:
In adult humans and pig models, strain rate (SR) correlates strongly with invasive measures of contractility but does not demonstrate a force-frequency relationship, which is a fundamental behavior of myocardial contraction. Given the considerable maturational changes of the myocardium from fetal stages to adulthood, extrapolation of adult findings to the young heart may not be appropriate. We sought to evaluate the SR response of the immature heart to increased heart rate (HR) and inotropic stimulation.
Methods:
The study consisted of two parts. In part 1, children without obvious structural or functional cardiac abnormalities were evaluated following successful radiofrequency ablation. Echocardiography was performed at baseline HR and then with atrial pacing and isoprenaline infusion titrated to achieve 130% of baseline HR. Left ventricular (LV) speckle tracking-derived SR and tissue Doppler isovolumic acceleration (IVA, a load-independent marker of contractility) were measured. In part 2, young piglets were submitted to atrial pacing at 200, 230, and 260 bpm. Invasive LV dP/dt was assessed, and speckle tracking-derived SR was measured at all stages. Repeated measures analysis of variance was used for comparison with baseline values.
Results:
In part 1, the LV SR and IVA (septal and lateral) in 23 children (ages 7.8-17.5 years) increased significantly with pacing and isoprenaline infusion (P < .001). In part 2, SR and invasive dP/dt increased significantly with increasing HR in young piglets (1-17 days; P < .01 and P < .001, respectively). Both LV SR and dP/dt plateaued at highest HRs concurrent with the decrease in LV end-diastolic dimension from baseline (73.0% ± 9.9% of the baseline value at 260 bpm; P < .001).
Conclusions:
SR in children is augmented with chronotropic and inotropic stimulation and in young infant piglets with chronotropic stimulation; in both children and piglets it has a force-frequency relationship, a behavior that is consistent with a measure of contractility.
