Modelling mitral valvular dynamics–current trend and future directions

Dysfunction of mitral valve causes morbidity and premature mortality and remains a leading medical problem worldwide. Computational modelling aims to understand the biomechanics of human mitral valve and could lead to the development of new treatment, prevention and diagnosis of mitral valve diseases. Compared with the aortic valve, the mitral valve has been much less studied owing to its highly complex structure and strong interaction with the blood flow and the ventricles. However, the interest in mitral valve modelling is growing, and the sophistication level is increasing with the advanced development of computational technology and imaging tools. This review summarises the state-of-the-art modelling of the mitral valve, including static and dynamics models, models with fluid-structure interaction, and models with the left ventricle interaction. Challenges and future directions are also discussed

Understanding the blood flow in realistic and idealised models of the pulmonary bifurcation

Adults patients with congenital heart disease are at risk of chronic complications including dysfunction of the pulmonary valve and narrowing of the branch pulmonary arteries [1]. Understanding the hemodynamic environment of the pulmonary bifurcation in these patients, is of immense importance, to prevent the clinical consequences of abnormal lung development and elevated pulmonary vascular resistance [2]. The aim of this study is to numerically investigate the blood flow characteristics in the pulmonary trunk of adults with congenital heart defects. In this work, we present results from a parametric analysis conducted, to study the effect of variations in morphology and boundary conditions. Blood flow simulations were performed in idealised and realistic geometries of the pulmonary arteries. The fluid was considered incompressible and governed by the Navier-Stokes equation. Local velocities, wall shear stress values and pressure ratios were evaluated in all cases. The flow was also examined in the case of a model with a static idealised pulmonary valve and by accounting the elasticity of arterial walls. The computational results indicate that the hemodynamic environment and the wall shear stress distribution are affected by variations in morphology and boundary conditions. The pressure in the left pulmonary artery was found higher than the right and main arteries, but reduced in the presence of stenosis. Downstream pressure conditions altered the flow in the pulmonary arteries and explained realistic flow splits between the branches. Different flow patterns were also noticed when pulmonary valve and elasticity of arterial walls are included in the pulmonary arterial models. Computational fluid dynamics is a powerful tool that has been utilised in this study to investigate blood flowing the pulmonary arteries under a range of geometrical characteristic and boundary conditions. Notable differences are noticed in the flow of the stenotic models or when pressure difference is assigned in the branch outlets. Modelling the pulmonary valve and the elasticity of the arterial wall are important parameters to consider in the computational models

Blood flow in the pulmonary bifurcation under healthy and diseased conditions

Adult patients with congenital heart disease are at risks of chronic complications including pulmonary regurgitation [1] and stenosis in the left pulmonary branch [2]. Long-term pulmonary stenosis is also associated with abnormal lung development and elevated pulmonary vascular resistance [3]. In this study, the haemodynamic environment of the pulmonary bifurcation is investigated, assuming different physiological and pathological cases based on various geometries and boundary conditions. Within the finite volume method framework of OpenFOAM®, blood flow simulations were performed in simplified two- and three-dimensional models of the pulmonary bifurcation. Newtonian and non-Newtonian blood rheology was considered for incompressible fluid flow governed by the Navier-Stokes equations. The simulation results demonstrated that the pulmonary arterial flow can be significantly affected by different geometrical characteristics and boundary conditions. Flow separation varied in models with different branch angle, origin, and obstruction. Local stenosis in the left pulmonary artery had a notable effect in the axial velocities and shear stresses developed on the vessel wall. Peripheral stenosis and pressure difference in the branch outlets resulted in variations in the branch flow splits, representative of pulmonary hypertension conditions. The branch pressure ratio was further analysed, based on disease severity, as an indicator of flow discrepancies between the different cases. The obtained results were comparable to flow simulations in a three-dimensional model, for both steady and unsteady flow. Future work will involve simulations in more complex patient-specific geometries from patients with congenital heart diseases. Peripheral resistances and patient-specific blood flow inlet waveform will be also considered

Zoom and its discontents: group decision making in pediatric cardiology in the time of COVID (and beyond)

The emergence of Covid-19 has led to change within hospital-based healthcare. An example, has been to reconfigure clinical decision making meetings from traditional in-person (Face-to-face, FtF) to online video-conferencing (VC) format inorder to decrease contagion risk. Despite its widespread uptake, there is minimal empirical data evaluating this format. This narrative review considers the implications on medical decision-making when clinicians communicate remotely via Microsoft Teams. The discussion is informed by the psychological literature and by commentary obtained from a survey of paediatric cardiac clinicians who participated in clinical meetings when video-conferencing was first introduced. Whist video-conferencing can optimize clinician presence, this is potentially offset by compromises in current imaging quality, the group discussion, information sharing and decision quality. Implementing a shift from face-to-face to VC within the group decision-making process requires an appreciation of the changed environment, appropriate adaptations and the implemention of new technology solutions. Meanwhile, healthcare should carefully consider the potential implications of clinical decision making using online video conferencing, be prepared to adapt and evaluate prior to a shift away from face-to-face formats

Tissue Doppler imaging following paediatric cardiac surgery : early patterns of change and relationship to outcome

In this study, tissue Doppler imaging (TDI) was used to assess changes in ventricular function following repair of congenital heart defects. The relationship between TDI indices, myocardial injury and clinical outcome was explored. Forty-five children were studied; 35 withcardiac lesions and 10 controls. TDI was performed preoperatively, on admission to paediatric intensive care unit (PICU) and day 1. Regional myocardial Doppler signals were acquired from the right ventricle (RV), left ventricle (LV) and septum. TDI indices included: peak systolicvelocities, isovolumetric velocities (IVV) and isovolumetric acceleration (IVA). Preoperatively, bi-ventricular TDI velocities in the study groupwere reduced compared with normal controls. Postoperatively, RV velocities were significantly reduced and this persisted to day-1 (PreOp vs. PICU and day-1: 7.7+2.2 vs. 3.4+1.0, P < 0.0001 and 3.55+1.29, P < 0.0001). LV velocities initially declined but recovered towards baseline by day-1 (PreOp vs. PICU: 5.31+1.50 vs. 3.51+1.23, P < 0.0001). Isovolumetric parameters in all regions were reduced throughout the postoperative period. Troponin-I release correlated with longer X-clamp times (r=0.82, P < 0.0001) and reduced RV velocities (r=0.42, P=0.028). Reduced pre- and postoperative LV velocities correlated with longer ventilation (PreOp: r=0.54, P=0.002; PostOp: r=0.42, P=0.026). This study identified reduced postoperative RV velocities correlated with myocardial injury while reduced LV TDI correlated with longer postoperative ventilation

Impaired cardiac autonomic nervous control after cardiac bypass surgery for congenital heart disease

We undertook a study to describe changes in heart rate variability (HRV) postoperatively in children undergoing cardiac bypass surgery for congenital heart disease (CHD). HRV was recorded for a 1-h period preoperatively and a 24-h period postoperatively in 20 children with CHD. We found a highly significant reduction in HRV in both time and frequency domain indices compared to preoperative values, which was sustained throughout the 24-h study period. There was a negative correlation between both time and frequency domain HRV measurements and length of cardiac bypass. HRV is reduced postoperatively and correlates with cardiac bypass time. Length of cardiac bypass time may be one mechanism whereby HRV is reduced following surgery

Hemodynamics in the pulmonary bifurcation in relation to adults with congenital heart disease : effect of branching angle and origin

Pulmonary regurgitation is the most common, clinically-important, complication that affects an increasing population of adult patients with congenital heart disease, primarily with repaired tetralogy of Fallot. Without intervention, the condition can lead to abnormal dilatation of the right ventricle, arrhythmias, heart failure, or death. Pulmonary valve replacement (PVR) is a frequent reoperation, the clinical decision for which is currently relying on symptoms, including arrhythmias and measures of the right ventricular volume. However, there is no common consensus on the reliability of these criteria and further studies are needed for an accurate and timely assessment for PVR treatment. The overall objective of this work is to hemodynamically characterise the pulmonary bifurcation in adult patients with congenital heart disease, pre- and post-operatively, and help establish novel metrics for a more accurate assessment for PVR, contributing to better surgical planning. In this study, we present preliminary computational fluid dynamic results in simplified models of the pulmonary trunk and its branches, in order to investigate the effect of the bifurcation angle on the flow. Physiological vessel dimensions and boundary conditions were used, in both symmetric and asymmetric geometries, and blood flow was simulated by solving the incompressible Navier-Stokes equations. Increase of the branching angle altered the flow development within the bifurcation, and had evident effects on the flow separation downstream of the junction. Shear stresses on the wall connecting the two artery branches were found, for the first time, dependent also on the origin of each branch, having a greater effect on the left pulmonary artery. These results demonstrate the impact of geometry on velocity, pressure, and wall shear stresses in the pulmonary bifurcation and contribute to a better understanding of the underlying flow mechanisms. Future studies will involve 3D reconstruction of patient-specific models of the pulmonary bifurcation, obtained from MRI images of adult patients with repaired tetralogy of Fallot, that need or have undergone pulmonary valve replacement

Computation of blood flow in the pulmonary bifurcation : towards a more effective treatment for adults with congenital heart disease

Adults with congenital heart disease represent an increasing population of patients that require repeated surgical interventions, most commonly for pulmonary valve replacement (PVR) and stenting [1]. Currently, the decision for treatment relies on symptoms, including arrhythmias and abnormal right ventricular volume and function [2], however the optimal timing for surgery remains unclear [3]. The aim of this work is to investigate the altered haemodynamic environment of the pulmonary bifurcation in adults with repaired tetralogy of Fallot, before and after pulmonary valve replacement. The overall objective is to derive a computational fluid dynamic metric to determine the optimal time for surgery. In this preliminary study, we present results in simplified geometries of the pulmonary trunk, focusing on the effects of geometry and flow conditions

Computation of blood flow in the pulmonary bifurcation : towards a more effective treatment for adults with congenital heart disease

Adults with congenital heart disease represent an increasing population of patients that require repeated surgical interventions, most commonly for pulmonary valve replacement (PVR) and stenting [1]. Currently, the decision for treatment relies on symptoms, including arrhythmias and abnormal right ventricular volume and function [2], however the optimal timing for surgery remains unclear [3]. The aim of this work is to investigate the altered haemodynamic environment of the pulmonary bifurcation in adults with repaired tetralogy of Fallot, before and after pulmonary valve replacement. The overall objective is to derive a computational fluid dynamic metric to determine the optimal time for surgery. In this preliminary study, we present results in simplified geometries of the pulmonary trunk, focusing on the effects of geometry and flow conditions

Blood flow simulations in the pulmonary bifurcation for the assessment of valve replacement in adult patients with congenital heart disease

Adult patients with congenital heart disease comprise a growing population with complex cardiac conditions, among other ageing-associated diseases. This particular group of patients may undergo multiple surgical procedures in their lifetime, a significant number of which involves pulmonary valve replacement (PVR). The clinical decision for such surgical intervention is currently relying on symptoms, including arrhythmias, and measures of right ventricular dilatation, at e.g. 80-90 mL/m2 end-systolic and 150-160 mL/m2 end-diastolic volumes [1,2]. However, there is no common consensus on the reliability of these criteria, and more accurate and timely assessment for PVR treatment is necessary. The overall objective of this work is to investigate the altered haemodynamic environment in the adult with congenital heart defect, including pre- and post-operative conditions. Here, we show computational results in the pulmonary bifurcation with the scope to establish a novel and reliable metric for pulmonary valve replacement