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Title: Characterising the function of the systemic right ventricle in hypoplastic left heart syndrome using cardiac magnetic resonance imaging
Author: Wong, James Kai-Bun
ISNI:       0000 0004 8500 6937
Awarding Body: King's College London
Current Institution: King's College London (University of London)
Date of Award: 2019
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Background: Children born with hypoplastic left heart syndrome (HLHS) have a LV too small to support the circulation. They undergo surgery resulting in the right ventricle (RV) supporting the systemic circulation. Accurately assessing systemic RV function is challenging but important as patients experience early circulatory failure. MRI is well established as a tool for assessing congenital heart disease. The technology is advancing allowing us to study the impact of energy, motion and shape on ventricular function. Characterising these factors in relation to HLHS might provide new insights into this condition. Methods: A stepwise approach was used: 1. Ventricular work and function were studied at varying heart rates using MRI catheterisation techniques to study the work of the heart and understand the causes of exercise intolerance. 2. Continuing the energetic theme; a non-invasive 4D flow MRI sequence was translated into a tool to study intra-cardiac kinetic energy (KE) a measure of the useful work of the heart. This metric was used to devise a new biomarker based on the ratio of ejected to total systolic KE -the particle energy ejection fraction (PE EF). 3. Finally, computational processing tools were employed to study how different operations effect the shape and motion of the RV. Results: The major findings were: 1. The systemic RV displayed good contractility and relaxation but preload (p < 0.008) and stroke volume fell at higher heart rates indicating a limitation of blood flow due to the absence of a sub-pulmonary ventricle. 2. Early diastolic KE was adversely affected in HLHS by the presence of a larger left ventricle (LV) remnant which acts as a stiff non-compliant structure impeding relaxation. Altered KE indices meant we attempted to study a new metric of function based on KE - PE EF - which was lower in those with single ventricles (p < 0.001) and LV dysfunction (p = 0.01). 3. HLHS subjects receiving RV-to-pulmonary artery conduits compared to those receiving shunts demonstrated ventricular dilatation (p = 0.001), increased sphericity (p = 0.006) and reduced multi-axial strain which is a sensitive measure of function. Conclusions: Novel MRI approaches were used to assess energy, shape and motion in the systemic RV. Characterising ventricular function in these terms provided new insights into HLHS pathophysiology. Refining and implementing these MRI techniques could help guide management of this difficult condition.
Supervisor: Razavi, Reza ; Schaeffter, Tobias Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available