Characterising the function of the systemic right ventricle in hypoplastic left heart syndrome using cardiac magnetic resonance imaging

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

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.
Date of Award1 Nov 2019
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorReza Razavi (Supervisor) & Tobias Schaeffter (Supervisor)

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