Noninvasive Assessment of Contractility and Compliance of the Left Ventricle in Children: Myocardial Stiffness Measured Throughout the Cardiac Cycle by Shear Wave Imaging

Background: Intrinsic myocardial stiffness (MS) is load-independent, unlike most parameters to assess LV systolic and diastolic function. Pre-clinical studies have found good correlation between 1) peak-systolic MS and contractility (or ESPVR); 2) end-diastolic MS and compliance (or EDPVR). Shear wave imaging (SWI) by ultrafast ultrasound imaging allows MS measurement throughout the cardiac cycle. Methods (Fig 1): Five children with LV pressure-overload (LV-PO; 2 aortic stenosis, 3 coarctation) were studied during cardiac catheterization and there were 5 age-matched controls. Interventricular septal MS was measured by SWI every 100ms during the cardiac cycle, pre- and post-balloon dilation. ESPVR and EDPVR were assessed by pressure-volume loops by a pressure catheter and real-time 3D-echo volumes. Results (Fig 2): Peak-systolic MS was higher in LV-PO (22.7±6.7 kPa) than controls (8.4±2.8 kPa; p<0.01) and compared to end-diastolic MS (LV-PO 4.8±1.7 kPa, control 1.3±0.8 kPa; p<0.01). End-diastolic MS was correlated with LV end-diastolic pressure (r=0.74). Relief of PO did not change the peak MS in the LV-PO (p=0.88). Correlations between peak-systolic MS and ESPVR (r=0.72), and between end-diastolic MS and EDPVR (r=0.79) were confirmed. Conclusions: Non-invasive MS is a load-independent measure of LV systolic contractility and diastolic compliance in children.