Impact of Ventricular Geometrical Characteristics on Myocardial Stiffness Assessment using Shear Wave Velocity in Healthy Children and Young Adults

Diastolic myocardial stiffness (MS) can serve as a key diagnostic parameter for congenital or acquired heart diseases. Using shear modulus and shear wave velocity (SWV), shear wave elastography (SWE) is an emerging ultrasound-based technique that can allow non-invasive assessment of MS. However, MS extrinsic parameters such as left ventricular geometrical characteristics could impact on shear wave propagation.To determine a range of normal values of MS using SWE in age groups of healthy children and young adults and to explore the impact of left ventricular geometrical characteristics on SWE.60 healthy volunteers (HVs) were recruited in the study and divided into 2 groups: "neonates" (0-1-month-old, n=15) and ">1 month old" (1 month - 45 years, n=45). SWE was performed using the Verasonics Vantage systems with a phased array ultrasound probe. The anteroseptal basal segment was assessed in two views. SWE was ECG-triggered during the end-diastolic phase. Conventional echocardiography was achieved to assess ventricular function and anatomy. Results are presented as stiffness values along with mean velocity measurements and SD. Simple and multivariate linear regression analysis were performed.For neonates, mean MS was 1.87 ± 0.79 kPa [min = 0.59 kPa; max = 2.91 kPa; SWV = 1.37 ± 0.57 m/s] with high variability and no correlation with age (p=0.239). For this age group, no statistically significant correlation was found between MS and any demographic or echocardiographic parameters (p>0.05). For ">1 month old" group, mean MS value of 1.67 ±0.53 kPa was observed [min 0.6 kPa, max 3 kPa; SWV = 1.29 ± 0.49 m/s] for HV. When age-paired, no sex-related difference was observed (p=0.55). In univariate linear regression analysis, age (r=0.83, p<0.01), diastolic interventricular septum thickness (IVSd, r=0.72, p<0.01), and left ventricle end-diastolic diameter (r=0.67, p<0.01) were the parameters with the higher correlation coefficient with MS. In a multiple linear regression analysis incorporating these three parameters as cofounding factors, age was the only statistically significant parameters (r=0.81, p=0.02).Diastolic MS has a linear increase in children and young adults. Diastolic MS correlates more robustly with age than with myocardial and left ventricular geometrical characteristics. However, the geometry impacts on the SWV implying the need to determine well established boundaries through future studies for the clinical application of the SWE.