Reference Values of Noninvasive Myocardial Work Indices Measured by Echocardiography in Healthy Children

Abstract

Backgroud: Noninvasive myocardial work, estimated by left ventricular (LV) pressure-strain loop (PSL), has been introduced for assessing LV myocardial performance. Based on both blood pressure and speckle-tracking derived strain data, noninvasive myocardial work is considered to be less load-dependent than global longitudinal strain (GLS). In some conditions, such as hypertension or aortic coarctation, the increased afterload will affect strain measurements, and myocardial work can serve as a more robust metric.

Objective: We prospectively recruited healthy children to explore the relationship between myocardial work indices and body size parameters, and to determine the reference values of noninvasive myocardial work indices in healthy children.

Methods: 183 healthy children (aged 1-18 years, males: 52.5%) were enrolled in the study. Global work index (GWI), global constructive work (GCW), global wasted work (GWW), global work efficiency (GWE), were assessed by LVPSL and compared according to age and sex.

Results: The mean for GWI was 1,448.7 ± 265.0 mm Hg%, 1,859.8 ± 290.7 mm Hg% for GCW, and the median (interquartile range) for GWW was 54.0 (33.0-82.0) mm Hg% and 97.0 (95.0-99.0) % for GWE. male had greater GWI and GCW) than female (1,572.5 ± 250.2 mm Hg% vs. 1,312.2 ± 208.7 mm Hg% and 1,944.3 ± 299.2 mm Hg% vs. 1,766.6 ± 251.5 mm Hg%, respectively, all P < 0.001). GWI and GCW were significantly correlated with baseline parameters, including age, height, weight, BSA, body mass index, heart rate, and blood pressure. After indexed to BSA, GWI (BSA), GCW (BSA) remained significantly negatively correlated with age (P < 0.001).

Conclusions: we proposed the normal reference values and regression equations for GWI and GCW based on age and BSA in healthy children. This might provide a basis of reference for the evaluation of cardiac function in children with cardiopulmonary disease.

Keywords: echocardiography; myocardial work; normal value; pediatric; reference value.

Figure 1

Flow chart detailing the identification of the study cohort (A) and image analysis for myocardial work indices (B). Eventing time was determined based on the Doppler flow spectrum of the aortic valve (a) and mitral valve (b). Tracking was automatically performed to determine segmental and global longitudinal strain (c). After entering the cuff blood pressure value (d), the software automatically generated the PSL curve and myocardial work indices (e). The lower right corner of figure e displays the myocardial work indices obtained from the PSL curve. PSL, pressure-strain loop.

Figure 2

Bar graphs showing average global work index (A), global constructive work (B), global wasted work (C), and global work efficiency (D) in different age subgroups. ^aP < 0.05 vs. age 1–3 years; ^bP < 0.05 vs. age 4–6 years; ^cP < 0.05 vs. age 7–9 years; ^dP < 0.05 vs. age 10–12 years; ^eP < 0.05 vs. age 13–15 years.

Figure 3

Impact of age on GWI (BSA) (A), GCW (BSA) (B), Lines represent mean and 95% confidence interval. GWI (BSA), GCW (BSA) indicate global work index, global constructive work indexed to body surface area.

Figure 4

The Bland–Altman analysis for assessing intra-observer variability of global work index, global constructive work, global wasted work, and global work efficiency. Lines represent bias and 95% limits of agreement for measurements performed in 20 subjects.

Figure 5

The Bland–Altman analysis for assessing inter-observer variability of global work index, global constructive work, global wasted work, and global work efficiency. Lines represent bias and 95% limits of agreement for measurements performed in 20 subjects.