Aspects of surgery for congenital ventricular septal defect

In chapter 1, an outline of the thesis is given. This thesis focuses on aspects of surgical closure of a congenital ventricular septal defect. In Chapter 2, the accuracy and the potential of 3-D echocardiography in the preoperative assessment of a congenital VSD were evaluated. 3-D echocardiography can be considered a valuable diagnostic tool, which may accurately identify the location, size, and spatial relations of a VSD. Chapter 3 presents a surgical alternative by temporary tricuspid valve detachment, in the approach for the repair of a congenital VSD in patients in whom transatrial exposure of the VSD is inadequate. The procedure was significantly associated with patients that were younger, lighter in weight, shorter and more often on diuretic therapy. Regardless of the age, size and preoperative clinical condition of the patients, and regardless of the right ventricular load, temporary detachment of the tricuspid valve in closure of a congenital VSD can be performed safely, without any negative effect on growth or function of the valve at medium-term follow-up. Chapter 4 comments on temporary chordal detachment as an alternative to temporary detachment of the anterior or septal tricuspid leaï¬,et from the tricuspid annulus in repairing a congenital VSD in patients in whom transatrial exposure of the VSD is incomplete. This technique may be useful in selected cases; however, arguments in favour should preferably come from obvious advantages or from careful follow-up. Chapter 5 focuses on the differences between mild (32°C) and moderate (28°C) systemic hypothermia during the reconstruction of a congenital ventricular septal defect in paediatric patients. No differences were found regarding organ preservation and adequacy of cardio pulmonary bypass, nor in surgical exposure and clinical outcome. Chapter 6 demonstrates the clinical application of real time 3-D echocardiography in patients with a surgically corrected congenital ventricular septal defect. With I-Space technology, the complex postoperative cardiac anatomy of the closed congenital VSD can be appropriately visualised in virtual reality and provides a unique resource for postoperative quality control as well as for education with regard to the intracardiac repair of a congenital VSD. Chapter 7 provides a long-term follow-up study after surgical closure of a congenital ventricular septal defect. To enhance surgical exposure of the congenital ventricular septal defect in selected patients, the tricuspid valve was temporary detached from the tricuspid annulus and proved to be a safe method. Closure of a congenital ventricular septal defect can be performed with a low complication rate. Tricuspid valve detachment (TVD) results in less early postoperative tricuspid valve regurgitation and does not result in tricuspid valve dysfunction during follow-up. TVD results in comparable residual shunting as non-TVD. The incidence of trivial residual shunting is higher in small children irrespective of tricuspid valve detachment. Trivial residual shunting is expected to disappear spontaneously Chapter 8 provides a long-term follow-up study after surgical closure of a congenital ventricular septal defect at adult age with special emphasis to quality of life. The need for surgical closure of a congenital ventricular septal defect in adulthood is rare, but on the right indication, surgery is an adequate and safe procedure, with good results on long-term follow up. Quality of life of this adult VSD group is comparable with general population. In 10 out of twelve domains of the TAAQOL-questionnaire they had an equal score. Merely in 2 domains, cognitive functioning and sleep, our population differed from the general population with regard to the quality of life. Chapter 9 contains a general discussion regarding aspects of surgery of a co

Towards Patient Specific Mitral Valve Modelling via Dynamic 3D Transesophageal Echocardiography

Mitral valve disease is a common pathologic problem occurring increasingly in an aging population, and many patients suffering from mitral valve disease require surgical intervention. Planning an interventional approach from diagnostic imaging alone remains a significant clinical challenge. Transesophageal echocardiography (TEE) is the primary imaging modality used diagnostically, it has limitations in image quality and field-of-view. Recently, developments have been made towards modelling patient-specific deformable mitral valves from TEE imaging, however, a major barrier to producing accurate valve models is the need to derive the leaflet geometry through segmentation of diagnostic TEE imaging. This work explores the development of volume compounding and automated image analysis to more accurately and quickly capture the relevant valve geometry needed to produce patient-specific mitral valve models. Volume compounding enables multiple ultrasound acquisitions from different orientations and locations to be aligned and blended to form a single volume with improved resolution and field-of-view. A series of overlapping transgastric views are acquired that are then registered together with the standard en-face image and are combined using a blending function. The resulting compounded ultrasound volumes allow the visualization of a wider range of anatomical features within the left heart, enhancing the capabilities of a standard TEE probe. In this thesis, I first describe a semi-automatic segmentation algorithm based on active contours designed to produce segmentations from end-diastole suitable for deriving 3D printable molds. Subsequently I describe the development of DeepMitral, a fully automatic segmentation pipeline which leverages deep learning to produce very accurate segmentations with a runtime of less than ten seconds. DeepMitral is the first reported method using convolutional neural networks (CNNs) on 3D TEE for mitral valve segmentations. The results demonstrate very accurate leaflet segmentations, and a reduction in the time and complexity to produce a patient-specific mitral valve replica. Finally, a real-time annulus tracking system using CNNs to predict the annulus coordinates in the spatial frequency domain was developed. This method facilitates the use of mitral annulus tracking in real-time guidance systems, and further simplifies mitral valve modelling through the automatic detection of the annulus, which is a key structure for valve quantification, and reproducing accurate leaflet dynamics

Modelling and application of mitral valve dynamics for reproducing the flow in the left ventricle of the human heart

The fluid dynamics in the left ventricle of the human heart is considered an important player for the prediction of long term cardiovascular outcome. To this end, numerical simulations represent an important tool for integrating the existing medical imaging technology and uncover physical flow phenomena. This study presents a computational method for the fluid dynamics inside the left ventricle designed to be efficiently integrated in clinical scenarios. It includes an original model of the mitral valve dynamics, which describes an asymptotic behavior for tissues with no elastic stiffness other than the constrain of the geometry obtained from medical imaging; in particular, the model provides an asymptotic description without requiring details of tissue properties that may not be measurable in vivo. The advantages of this model with respect to a valveless orifice and its limitations with respect to a complete tissue modeling are verified. Its performances are then analyzed in details to ensure a correct interpretation of results. It represents a potential option when information about tissue mechanical properties is insufficient for the implementations of a full fluid-structure interaction approach. Geometries of left ventricle (LV) and mitral valve (MV) are extracted from 4D-transesophageal echocardiography. MV geometries are extracted in open and closed configurations and the intraventricular fluid dynamics is reproduced by a dedicated approach to direct numerical simulation (DNS) that includes flow-tissue interaction for the MV leaflet (Collia et al. 2019). This approach is applied to normal and pathological ventricles to investigate the dynamics of the MV during the cardiac cycle: how it interacts with the ventricular flow and how it affects clinical measurements. The dynamics of mitral opening at the onset of diastole, as well as the closure at the transition between diastole and systole, is governed by the high pressure gradients associated with the bulk cardiac flow. On the opposite, during the flow diastasis in the middle of the diastolic filling, valvular motion is primarily influenced by the intraventricular circulation that gives an increased tendency to close in enlarged ventricles. This observation provides a physical interpretation to echocardiographic measurements commonly employed in the clinical diagnostic process. Results demonstrated the properties of false regurgitation, blood that did not cross the open MV orifice and returns into the atrium during the backward motion of the MV leaflets, whose entity should be accounted when evaluating small regurgitation (Collia et al. 2019). The regurgitating volume is found to be proportional to the effective orifice area, with the limited dependence of the LV geometry and type of prolapse. These affect the percentage of old blood returning to the atrium which may be associated with thrombogenic risk. This non-invasive method is useful for the assessment of blood flow, to improve early detection of cardiac dysfunctions and for provide a concrete helpful in clinical routines

Investigation into the 3D structure of the developing human fetal heart

Investigating the developmental processes of the human fetal heart is a challenging task. Few reports describe the morphological features during the first stage of heart maturation and consecutive developmental periods after cardiogenesis. Reasons for this include the difficulty of collecting suitable samples and the limitations of investigating modalities. This research was proposed to clarify the detailed morphological features of normal human fetal hearts in early-stage maturation, using post-mortem samples. These samples were analysed using high-resolution episcopic microscopy (HREM), and compared with the latest clinical imaging taken by 3D fetal echocardiography and compared with mouse samples. HREM, a newly-developed high-quality image modality, produces a computerbased 3D reconstruction which enables us to visualize detailed spatial structures of small specimens. HREM includes several procedural steps, which may affect the histological or morphological structures of samples, so I explored the potential effects. I found 12% shrinkage due to dehydration and polymerization. Therefore, while the general appearance of 3D reconstructed images looked identical to the pictures of the original heart samples, it is important to consider the effects of shrinkage when interpreting the morphological assessment by HREM. Normal human fetal hearts from the 9th to 11th weeks of postmenstrual gestation demonstrated unique morphological findings. Ventricular walls and trabeculations showed thick and random cellular structures. Atrioventricular and semilunar valves were also thick but histological maturation was observed within a few weeks after cardiogenesis. The great arterial walls were thick and comprised of dense cellular matrix. Morphologically, several characteristic findings, such as large atrial appendages, the developmental process of formation of the membranous ventricular septum and prominent coronary arteries, were recognised during this period. Heart size increased linearly with gestation. Normal human fetal hearts demonstrate geometrical development and histological and morphological maturation after the period of cardiogenesis. In comparison with human fetal hearts, mouse hearts demonstrate dramatic morphological alterations during a short maturation period. Fetal mouse hearts show some similar morphological findings to the human fetal heart, such as large atrial appendages, lack of formation of the membranous septum, and thickened great arterial walls. This suggests a shared mechanism of fetal heart maturation in mammals. Detailed clinical information regarding cardiac morphology is vital for accurate prenatal heart diagnosis in the first trimester. Fetal echocardiography in early gestation has become routine practice. However, the technical limitations of image acquisition and picture resolution make it difficult to visualize clear 3D images for fetal cardiac diagnosis. Current modalities for clinical investigation by 3D echocardiography do not have sufficient resolution to enable detailed morphological investigation of the human fetal heart between 10th to 12th weeks of postmenstrual gestation. Only the original data of the four-chamber view demonstrated no offsetting of the atrioventricular valves as seen on HREM. Further technical advances in 3D echocardiography will be required to enable precise cardiac diagnosis in the first trimester. This thesis describes morphological development in normal human fetal hearts for the first few weeks after cardiogenesis and contributes to a better understanding of the normal appearances in the first trimester which is vital for future investigation into the origin of congenital heart disease

Translating computational modelling tools for clinical practice in congenital heart disease

Increasingly large numbers of medical centres worldwide are equipped with the means to acquire 3D images of patients by utilising magnetic resonance (MR) or computed tomography (CT) scanners. The interpretation of patient 3D image data has significant implications on clinical decision-making and treatment planning. In their raw form, MR and CT images have become critical in routine practice. However, in congenital heart disease (CHD), lesions are often anatomically and physiologically complex. In many cases, 3D imaging alone can fail to provide conclusive information for the clinical team. In the past 20-30 years, several image-derived modelling applications have shown major advancements. Tools such as computational fluid dynamics (CFD) and virtual reality (VR) have successfully demonstrated valuable uses in the management of CHD. However, due to current software limitations, these applications have remained largely isolated to research settings, and have yet to become part of clinical practice. The overall aim of this project was to explore new routes for making conventional computational modelling software more accessible for CHD clinics. The first objective was to create an automatic and fast pipeline for performing vascular CFD simulations. By leveraging machine learning, a solution was built using synthetically generated aortic anatomies, and was seen to be able to predict 3D aortic pressure and velocity flow fields with comparable accuracy to conventional CFD. The second objective was to design a virtual reality (VR) application tailored for supporting the surgical planning and teaching of CHD. The solution was a Unity-based application which included numerous specialised tools, such as mesh-editing features and online networking for group learning. Overall, the outcomes of this ongoing project showed strong indications that the integration of VR and CFD into clinical settings is possible, and has potential for extending 3D imaging and supporting the diagnosis, management and teaching of CHD

Combined numerical and morphological study of the heart: development of a scalable mitral valve morphometric model and assessment of modelling criteria for the right atrium

Frameworks for the computational modelling of heart components are continuously evolving, either to create models in a faster manner, or to represent its components more accurately. The mitral valve on the left side of the heart, for example, has a very complex geometry, and shape alterations induced by surgical procedures affect the long-term restoration of function. While several frameworks that recreate mitral valve shape from patient-specific images have been developed, allowing for the development of computational simulations of pre- and post-repaired cases, they are not flexible enough to yield a variety of models. On the other hand, accurate computational models of the right side of the heart are lacking, and since the right heart is used as a platform for clinical treatments such as haemodialysis, the development and validation of a computational model representing its function is necessary. The overall aim of this thesis was to develop computational modelling frameworks for two components of the heart: the mitral valve on the left side, and the right atrium on the right side. A mathematical evaluation of mitral valve morphometry through correlation analysis and evaluation of prediction equations for its shape was performed by using imaging datasets obtained in collaboration with clinicians and from the literature. This information led to the development of a computational toolbox enabling the quick generation of anatomically accurate and clinically useful parametric models of the mitral valve. This toolbox, implemented in MATLAB, generates the mitral valve geometry and respective mesh, and assigns boundary conditions and material properties, necessary for finite element analysis. A sensitivity analysis of boundary conditions was performed to determine their influence on mitral valve biomechanics, with the chosen conditions being incorporated in the tool. A healthy valve geometry was generated and analysed, and the respective computational predictions for valve physiology were validated against data in the literature. Moreover, two patient-specific mitral valve models including geometric alterations associated with disease were generated and analysed. Mitral valve function was compromised in both models, as given by the presence of regurgitating areas, elevated stress on the leaflets and unbalanced subvalvular apparatus forces. These results showcase the importance of a healthy mitral valve shape for adequate function; further, they demonstrate the potential of the computational toolbox, which allows for the automatic finite element analysis of the mitral valve in a variety of clinical cases, useful to study the biomechanics of patient-specific shapes. In addition, a physiological blood flow model of the right atrium was developed and validated against data in the literature. This model was used as a simulation platform to evaluate the performance of four catheter designs for haemodialysis: while the symmetric tip had the best haemodynamic results, associated with low recirculation of flow and shear stress values, the step tip designs yielded the worst haemodynamic outcomes. The presence of side holes at the tip led to a decrease in recirculating flow, associated with improved catheter performance. The present simulation platform therefore enables the assessment of the performance of several catheter designs before their release on the market. The work presented in this thesis bridges engineering and medicine through the development of two computational frameworks with primary clinical objectives: a computational tool for the evaluation of mitral valve biomechanics for a variety of geometries and assessment of current and novel mitral interventions; and a right atrium simulation platform which potentially highlights haemodialysis catheter design features requiring optimisation for optimal performance

Front Lines of Thoracic Surgery

Front Lines of Thoracic Surgery collects up-to-date contributions on some of the most debated topics in today's clinical practice of cardiac, aortic, and general thoracic surgery,and anesthesia as viewed by authors personally involved in their evolution. The strong and genuine enthusiasm of the authors was clearly perceptible in all their contributions and I'm sure that will further stimulate the reader to understand their messages. Moreover, the strict adhesion of the authors' original observations and findings to the evidence base proves that facts are the best guarantee of scientific value. This is not a standard textbook where the whole discipline is organically presented, but authors' contributions are simply listed in their pertaining subclasses of Thoracic Surgery. I'm sure that this original and very promising editorial format which has and free availability at its core further increases this book's value and it will be of interest to healthcare professionals and scientists dedicated to this field