Behaviour of natural myocardial shear waves in children and adolescents: determinants and reproducibility

Abstract Funding Acknowledgements Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): Egyptian ministry of higher education and research Background Ultrafast echocardiography allows the direct non-invasive assessment myocardial shear waves (SW). These waves are naturally generated after mitral valve closure (MVC) and aortic valve closure (AVC) and their propagation velocities has been found to be linked to myocardial stiffness (MS) in adults. However, little experience exist regarding behaviour of such waves in children and normal values of SW velocities in children are lacking. Purpose This study aimed at setting up a reference range for SW velocities in paediatrics, determining influencing factors and exploring the reproducibility of their measurements in children. Methods One hundred-four healthy children (mean age 10 ±4 years old; range 2–18 years) were recruited. Participants were scanned with a research ultrasound scanner using divergent waves to yield a high frame rate of 1580 ±113 Hz. Parasternal long axis views (PLAX) were recorded for offline analysis. An anatomical M-mode was drawn along interventricular septum to visualize the propagation of shear waves after both MVC and AVC. Tissue Doppler acceleration maps were extracted and SW velocities were measured semi-automatically as the spatiotemporal slope of these waves (figure 1). Intra-class correlation coefficient (ICC) (2-way mixed model, absolute agreement between single measures) was used to check the reproducibility of these measurements among three raters. Results SW propagation velocities showed an association with clinical variables ; age (Figure2), body mass index (BMI) and body surface area (BSA). In addition, SW speeds showed association with local cardiac factors; ventricular septal thickness, LV mass and left ventricular end-systolic (LVESV) & end-diastolic volumes (LVEDV). Using a multivariate model; predictors of SW velocities after MVC are: age and LV mass (R2=0.59), while predictors of SW after AVC are: age, LV mass and LV volumes (R2= 0.33). In twenty-five randomly selected participants, moderate to good inter-observer reliability were noted among the three observers (ICC 0.84 [CI 0.70 to 0.92] after MVC, and ICC 0.83 [CI 0.69 to 0.92] after AVC). Conclusions Naturally occurring myocardial shear waves in children can easily be measured with acceptable reproducibility. Values are lower than in adults. SW velocities in children showed clear dependency on age, presumably due to growing heart size and increased myocardial muscle mass.