Heba Aguib

Aortic root dynamism, geometry, and function after the remodeling operation: Clinical relevance

Objectives Valve‐conserving operations for aneurysms of the ascending aorta and root offer many advantages, and their use is steadily increasing. Optimizing the results of these operations depends on providing the best conditions for normal function and durability of the new root. Methods Multimodality imaging including 2‐dimensional echocardiography, multislice computed tomography, and cardiovascular magnetic resonance combined with image processing and computational fluid dynamics were used to define geometry, dynamism and aortic root function, before and after the remodeling operation. This was compared with 4 age‐matched controls. Results The size and shape of the ascending aorta, aortic root, and its component parts showed considerable changes postoperatively, with preservation of dynamism. The postoperative size of the aortic annulus was reduced without the use of external bands or foreign material. Importantly, the elliptical shape of the annulus was maintained and changed during the cardiac cycle (&Dgr; ellipticity index was 15% and 28% in patients 1 and 2, respectively). The “cyclic” area of the annulus changed in size (&Dgr;area: 11.3% in patient 1 and 13.1% in patient 2). Functional analysis showed preserved reservoir function of the aortic root, and computational fluid dynamics demonstrated normalized pattern of flow in the ascending aorta, sinuses of Valsalva, and distal aorta. Conclusions The remodeling operation results in near‐normal geometry of the aortic root while maintaining dynamism of the aortic root and its components. This could have very important functional implications; the influence of these effects on both early‐ and long‐term outcomes needs to be studied further.

Spatial Orientation and Morphology of the Pulmonary Artery: Relevance to Optimising Design and Positioning of a Continuous Pressure Monitoring Device.

Personalised treatment of heart disease requires an understanding of the patient-specific characteristics, which can vary over time. A newly developed implantable surface acoustic wave pressure sensor, capable of continuous monitoring of the left ventricle filling pressure, is a novel device for personalised management of patients with heart disease. However, a one-size-fits-all approach to device sizing will affect its positioning within the pulmonary artery and its relationship to the interrogating device on the chest wall on a patient-specific level. In this paper, we analyse the spatial orientation and morphology of the pulmonary artery and its main branches in patients who could benefit from the device and normal controls. The results could optimise the design of the sensor, its stent, and importantly its placement, ensuring long-term monitoring in patient groups.

Characterisation of spatiotemporal aortic flow and aortic wall biomechanics in coarctation

The thoracic aorta performs sophisticated functions which depends largely on its almost unique structure1. Coarctation of the aorta is a relatively common congenital anomaly, which causes a heavy burden of morbidity and mortality worldwide. As emphasized by Suradi and Hijazy in this issue of the journal, the long-term results can be very variable due to many factors. There is now a growing realization that the condition is associated with different forms of aortopathy, which are either a direct result of, or associated with, the narrowing2–4. These changes of the aorta can interfere with the long-term results of surgical correction of the anomaly and, therefore, need to be thoroughly defined and understood. Advances in modern imaging techniques, coupled with detailed computerized analysis, offer new opportunities to evaluate in vivo the mechano-biology of the arterial wall and the factors which could influence it, such as the spatiotemporal pattern of flow. Computational fluid dynamics (CFD) offers an opportunity to study both the fluid dynamics as well as its potential impact on the (patho-) physiology of the aortic wall5,6, (see Figure 1 and Figure ​Figure2).2). It allows quantification of flow, vortex formation, pressure gradients, wall shear stress (WSS) and other relevant parameters starting from the aortic valve through the coarcted area downstream towards the distal descending aorta, based on patient-specific 3D anatomical models of the aorta and magnetic resonance imaging (MRI) flow acquisition. Briefly, CFD analysis of a patient-specific vasculature involves the following steps: (1) reconstruction of vascular anatomy from medical images such as CT and MRI, (2) setting inflow and outflow conditions as well as properties of the blood, (3) running computations, and (4) post-processing to visualise and/or quantify the variables of interest. Figure 1. a) Flow patterns in a hypoplastic aortic arch ((left) systole, (right) diastole). The flow pathways are visualised by traces of virtual particles released in the aorta based on the CFD. High velocity flow through the hypoplastic arch leads to a hemodynamic ... Figure 2. Flow patterns (left) and endothelial shear stress (right) of a patient with calcified bicuspid aortic valve (BAV) and thoracic aortic aneurysm. The impact of the hemodynamic jet coming out through the BAV elevates the shear stress level on the endothelium ... Goubergrits et al.7 developed a CFD model to calculate peak systolic pressure drops in coarctation patients pre- and post-treatment. This is particularly relevant due to the fact that pre-operative geometries vary considerably, (Figure 3). The model demonstrated a strong correlation with catheter-based measurements in the aorta as well as flow patterns captured using 4D velocity CMR imaging. Another interesting study on the use of CFD to calculate cardiac workload and hemodynamic behaviour in different types of aortic arch obstruction was presented by Coogan et al.8. The above examples demonstrate the potential of CFD as a functional imaging tool, by adding additional visualisation and quantification power to conventional diagnostic measurements such as CT and MRI. Figure 3. Anatomical models of different reconstructed cases representing aortic coarctation geometries7. More recently, 4D velocity CMR imaging (4D Flow) has been used in looking at fluid dynamics over the cardiac cycle. Using 4D Flow acquisition sequence and post-processing software, the propagation of blood – velocity and flow – through an arterial segment can be calculated over the cardiac cycle (Figure 4). Figure 4. Post-processing results of 4D velocity CMR images in a patient with aortic coarctation and poststenotic dilatation. Systolic 3D streamlines in the entire thoratic aorta and a magnified region encompassing the pathological site14. 4D velocity CMR imaging and quantification of cardiovascular hemodynamics are contributing to the understanding of cardiovascular pathologies: the combination of 3D spatial encoding, three-directional velocity encoding and cine acquisition provides data for the measurement and visualization of the temporal evolution of complex flow patterns throughout a 3D-volume9. Hope et al.10 showed that 4D velocity CMR imaging can help to evaluate collateral blood flow as a potential measure of hemodynamic significance in patients with aortic coarctation. Additionally, 4D Flow analysis showed distorted flow patterns in the descending aorta after coarctation repair. Considerable helical and vortical flow in regions of post-stenotic dilation were identified. The utility of 4D Flow to analyse and understand vascular geometry and systolic flow characteristics in a patient with restenosis in aortic coarctation, after surgical repair, is presented by Markl et al.11 (Figure 4). An early study by Kilner et al. 12 was published, describing helical and retrograde flows in normal aortic arch using three-directional cine velocity mapping (predecessor to 4D Flow). The development of flow through the two coronary cusp sinuses, the arch and the descending aorta was demonstrated at selected velocity mapping planes. Image acquisition as well as post-processing of 4D flow datasets require time and multi-disciplinary skills. Efficient synchronization considering cardiac and respiratory movements has a significant impact on image quality13,14. 4D Flow is not yet a part of the clinical routine of CMR examination, but its use should increase in specialized centres in the near future.

Opposing forces and a river into a lake: Relevance to coronary hemodynamics in Kawasaki disease

[first paragraph of article] Kawasaki disease (KD) continues to interest, intrigue, and challenge clinicians, basic scientists, and engineers. One of the defining features of the disease is the development of coronary aneurysms of varying sizes and shapes, reproducing the phenomenon of ‘‘River into a lake’’, and introducing profound changes in the coronary circulation. These changes reflect many physical, engineering and even cultural beliefs which might be of interest to the readers of this special issue of the Journal dealing with KD. Some of these ideas are presented in this article.

Utility of 4D Flow mapping in Eisenmenger syndrome with pulmonary atresia.

Management of patients with Eisenmenger syndrome with pulmonary atresia is challenging because of the complexity of the structure-function relationship of the components of the syndrome. Multi-modality imaging including cardiac magnetic resonance (CMR) 4D Flow offers unprecedented opportunities to unravel, at least in part, some of these components, and thus help in the management of these patients. In this study, we describe the use of these integrated methods with particular reference to CMR 4D Flow in a patient with Eisenmenger syndrome and pulmonary atresia and outline both the utility and the limitations. A comprehensive cardiac magnetic resonance (CMR) 4D Flow analysis was performed preoperatively and postoperatively, during peak systole, late systole, early diastole, and late diastole. The focus of the present study was to investigate the pattern of flow and dynamic changes at different levels of the aorta, as well as in the duct and the pulmonary arteries. Preoperatively, a right-handed helix and a vortex were observed in the dilated ascending aorta, and the duct flow was mainly dependent on reverse, upstream flow from the descending aorta, distal to the duct, during diastole, denoting low pulmonary vascular capacitance. Following repair, the flow in the ascending aorta and the descending aorta changed markedly. These changes included both timing and intensity of the right-handed helix, as well as the vortex in the ascending aorta. The significance of the observed changes in flow pattern and their influence on wall structure and function are discussed. Our study demonstrates the extremely powerful potential of CMR 4D Flow in the management of complex congenital anomalies.

Quantitative assessment of right ventricular structure and flow dynamics in pulmonary homograft obstruction

The insertion of cryopreserved homograft conduit into the pulmonary outflow tract is an effective method of relieving severe pulmonary valve dysfunction. A certain proportion of the inserted homografts undergo late degeneration resulting in progressive right ventricular outflow obstruction. When severe, this obstruction needs repeat intervention. The timing of this intervention is critical and depends on a thorough assessment of symptoms, coupled with detailed evaluation of right ventricular structure and function as well as flow dynamics in the right ventricular outflow. We report a patient who illustrates many of the issues related to management of these patients with particular reference to the use of modern imaging followed by detailed image processing.