Right ventricular energetics using blood speckle tracking in pediatric congenital heart disease

Abstract

This thesis is composed of three studies of right ventricular (RV) energetics in pediatric patients with congenital heart disease (CHD), using blood speckle tracking (BST). The objectives were to describe the RV energetics and flow dynamics in the context of various CHD resulting in adverse loading of the RV. We compared these patient groups with healthy controls. Paper 1: In this pilot study, we used BST to image RV flow patterns in children with large atrial septal defects (ASD) and those with repaired tetralogy of Fallot (rTOF) with severe residual pulmonary insufficiency (PI). This study included 57 participants: 21 with rTOF, 11 with large ASD, and 25 healthy individuals (CTL). Additionally, a flow phantom was utilized to evaluate the impact of imaging plane and smoothing adjustments on the parameter of energy loss (EL) obtained with BST. We observed that RV diastolic EL in ASD and rTOF was comparable, but both were higher than in CTL. High EL areas during systole were consistent across all groups, appearing in the RV outflow tract and near the tricuspid valve leaflets in early diastole. Notably, an extra area of early diastolic EL at the apex was identified in rTOF patients, related to the interaction of tricuspid inflow and PI. The flow phantom experiment indicated that while EL varied with imaging plane and smoothing settings, the overall EL trend remained stable if these settings were consistent. Paper 2: This study used BST to study of blood flow dynamics and patterns in the right ventricle and main pulmonary artery in pediatric pulmonary hypertension (PAH) compared to healthy controls. Eighteen subjects were included in each group. A diastolic vortex in the main pulmonary artery (MPA) was identified in 16 of the PAH patients, but not in controls. Significantly higher MPA systolic and diastolic EL, as well as increased vector complexity (VC) and diastolic vorticity were noted in PAH compared to controls. This study demonstrated abnormal flow patterns in the MPA with diastolic vortex formation in most patients with PAH. This diastolic vortex likely results from reflected waves from the distal pulmonary bed. Our data indicate that diastolic vortex could potentially be used in the diagnosis of PAH. Paper 3: This study included patients with univentricular hearts (UVH) after Fontan palliation and compared their intracardiac flow patterns to healthy controls. The UVH included 29 patients and 30 CTL. Qualitative vortex formation was similar between groups in systole and diastole except for double inlet left ventricle which had more complex inflow patterns consisting of colliding vortices. Quantitatively, UVH kinetic energy (KE), energy loss (EL) and vorticity (VO) were lower when compared to healthy controls. We also demonstrated a correlation between KE, EL and VO. We concluded that although similar vortex formation is preserved in well-functioning UVH after Fontan, the latter is an energy-deprived circulation where all mechanisms of energy conservation are important.