Personalised Simulation of Myocardium Electromechanics
and Pulmonary Valve Replacement Surgery in
Repaired Tetralogy of Fallot: a Case Study
1. Introduction: Medical Background and Challenges
Tetralogy of Fallot is a congenital heart disease that mainly affects the right ventricle (denoted as RV in the following). It occurs in about 1 child out of 2500 (Hoffman et al., 2002) and it is characterised by four heart defects:
- Inter-ventricular septal defect
- Pulmonic stenosis
- Hypertrophic right ventricle
- Overriding aorta
Because of these defects, Tetralogy of Fallot requires surgical repair early in infancy. Mortality and morbidity of this initial intervention is nowadays very low but the repair may lead to the destruction of the pulmonary valves. Regurgitations can appear, resulting in extreme dilation of the right ventricle and loss of cardiac function later during the child life. Pulmonary valve may thus be replaced to retrieve a normal cardiac function.
Determining the best time for re-intervention is a clinical challenge. Because the child is growing, replacing the valves too early may not be necessary and may result to be inefficient on the long term. Besides, valves lifetime is about 10 years. Hence, the earlier they are replaced, the earlier they must be changed, resulting in repeated interventions. On the other hand, waiting too much may result fatal. The extreme dilation of the right ventricle may cause arrhythmia or other electro-physiological troubles. Furthermore, if too dilated, the right ventricle may not be able to recover a normal function even after valve replacement.
Several pulmonary valve replacement strategies are available. In Health-e-Child, we are interested in two competing approaches:
- Pulmonary valve replacement alone. Usually, this pulmonary valves are replaced surgically but minimally-invasive techniques have been proposed recently (Khambadkone et al., Circulation 2005). With this approach, the heart adapts itself to its new conditions owing to natural remodelling.
- Pulmonary valve replacement and direct right ventricle remodelling. The surgeon not only replaces the valves but also resects any scars and fibrosis regions of the myocardium to improve the cardiac function and reduce the right ventricle volume (del Nido et al., 2006).
Nevertheless, choosing which therapy to apply for a given patient is nowadays complex. The effects of these therapies upon the cardiac function are difficult to predict. No clinical evidences nor rules have been found to help the cardiologists in taking the right decision.
Based on these clinical rationales, we investigate in Health-e-Child how cutting-edge image analysis algorithms and personalised electromechanical models of the heart can help in evaluating the cardiac function of a patient and can predict the effects of right pulmonary valve replacement therapies. To that purpose, we propose a three-step approach:
- Step 1: Building a patient-specific anatomical model of the heart from clinical gated cine-MRI.
- Step 2: Simulating patient cardiac function by personalising an electromechanical model of the heart
- Step 3: Simulating the two PVR therapies using soft-tissue intervention platform
The pipeline is tested on a young Health-e-Child patient (age=17). Details and first results of the experiments are presented in the following sections.
References
- Khambadkone, S., Coats, L., Taylor, A., Boudjemline, Y., Derrick, G., Tsang, V., Cooper, J., Muthurangu, V., Hegde, S. R., Razavi, R. S., Pellerin, D., Deanfield, J., and Bonhoeffer, P.: Percutaneous Pulmonary Valve Implantation in Humans: Results in 59 Consecutive Patients, Circulation 112(8), 1189–1197, 2005
- Hoffman, J.I.E., and Kaplan, S.: The incidence of congenital heart disease, Journal of the American College of Cardiology 39(12), Elsevier, 1890-1900, 2002
- del Nido, P. J.: Surgical Management of Right Ventricular Dysfunction Late After Repair of Tetralogy of Fallot: Right Ventricular Remodeling Surgery, Semin Thorac Cardiovasc Surg Pediatr Card Surg Annu. 9(1), 29-34, 2006