According to the article "Analysis of diagnosis and treatment focus of aortic arch dysplasia," jointly released by the Chinese Pediatric Surgical Cardiology Group in 2018 [10]: Although the five commonly used diagnostic methods have advantages, the proximal arch, the distal arch, and the isthmus are less than 60%, 50% and 40% of the diameter of the ascending aorta, respectively. However, it is easy to see that they all rely on the stenosis's diameter for evaluation. These diagnostic methods do not fully consider age, weight, large vessel development, hemodynamics, and other comprehensive conditions, so the accuracy of their criteria is undoubtedly compromised.
Color ultrasound is one of the leading inspection methods of COA [11]. Although it is possible to obtain direct signs of the aortic arch, the quality of ultrasound imaging is affected by the patient's sound transmission conditions. The descending part of the aortic arch and its collateral circulation cannot be displayed clinically in some patients. The operator must check intracardiac abnormalities individually. The technical requirements for the operator are high, leading to a missed diagnosis of aortic arch malformation. Studies have suggested that the missed diagnosis rate of color Doppler ultrasound in COA diagnosis is 5.4%. As color Doppler ultrasound cannot fully display the position relationship between the distal end of the aorta, the constricted segment, and the surrounding blood vessels, the operator must confirm the determination of parameters such as the length and position of the stenosis before operation through other imaging examinations to verify and determine the operation mode. Although pressure data can be directly obtained by vascular catheter pressure measurement, it is not commonly used because it is invasive, requires clinical anesthesia, and is expensive. The catheter and contrast agent can influence hemodynamics. Although MRI can objectively reflect the shape of the aorta, it has high requirements for the heart rate, machine serial number parameters, and electrocardiogram(ECG) gating technology of children, thus developing few institutions. The measured minimum diameter might be missed.
Computed tomographic angiography (CTA) is a method for obtaining intracardiac and extracardiac structural data with extremely spatial resolution using intravenous contrast agents and ionizing radiation [12]. CT allows the evaluation of these structures in 2D and provides the ability to reconstruct 3D data. For patients with poor preoperative arch imaging, CT angiography can be an excellent tool for surgical planning because CT imaging does not produce apparent artifacts on metal objects. This finding is useful for the foot arch imaging of patients who have previously used constriction stents [13]. The guide then clearly pointed out the importance of fluid mechanics at constriction but provided no other analysis methods or strategies.
An image-based computational fluid dynamics (CFD) approach based on Navier Stokes equations is therefore proposed and expected to solve, at source, the current state of the art in terms of the multiplicity of diagnostic criteria for this condition, diversity of treatment modalities, leading to "off" clinical diagnosis and treatment [14]. For example, preoperative diagnosis of aortic arch dysplasia without the need for severing anastomosis surgery after intraoperative release. Intraoperative anastomotic vascular tone is high and must be re-blocked by adding a vascular patch [15]. Postoperative color ultrasound has a significant difference but no clinical manifestations, how to decide whether to re-intervention, and other clinical problems. It is also expected to accurately predict the pressure drop [16, 17]. Furthermore, image-based CFD analysis of patient-specific hemodynamics may have relevance for predicting posttreatment hemodynamics and altered hemodynamics versus long-term outcomes in patients with pathological effects on the aorta [18–20]. Therefore, the present study addressed the clinical problem that preoperative diagnosis of COA provides limited information for comprehensive preoperative evaluation.
CFD—an emerging computer virtual mechanics technique [21]—is used to reconstruct geometric models after processing noninvasively acquired imaging images, perform simulated flow of fluids and obtain patient regions of interest by solving a series of equations, such as coronary artery and hemodynamic parameters in the aorta. The resulting fluid parameters should be used to determine disease severity, and the technology is used in various fields, including water engineering, chemical engineering, civil engineering, and medicine. CFD is also widely used in medical aspects such as the coronary artery, intracranial aneurysm, aortic dissection, and other arterial diseases. In COA diseases, CFD can be performed postprocessing based on CTA to reconstruct the aortic arch model. After fluid simulation, hemodynamic parameters were obtained. Hemodynamic parameters, such as pressure gradient and wall shear force gradient, play a noninvasive advantage over cardiac catheters, guiding diagnosis and determining treatment modality. Briefly, the imaging department reported on a narrow diameter and sometimes provided a narrow segment length, and the extent of resection was empirically analyzed using the master knife on CT film.
Intraoperatively, the external diameters were all thick, and after some resection, the internal diameters remained small. There was a reduction in tension bleeding but a little reduction in fear of restenosis. As the existing preoperative imaging report content is too few, diagnostic criteria and research usually focus on the "number" of aortic dysplasia, and it is possible to describe the parameters of a large number of aortic integrals. CFD can be used as an essential description to solve the current problem as it has largely replaced geometrical "algorithms" after the study of angles and proportions, which could not comprehensively reflect the whole picture of aortic dysplasia.
Image-based CFD is a promising approach; however, most of these methods are still in a purely academic state of research, and currently, whether image-based CFD applies to a wide range of cardiovascular diseases, such as abdominal aortic or cerebral aneurysms, congenital and acquired valvular heart diseases, and different CHDs, is under intense investigation [23, 24]. Therefore, through the analysis of fluid hemodynamics after three-dimensional reconstruction of CTA in 40 children with aortic arch constriction and 20 normal subjects in the clinic, from the fluidic diagram and pressure graph, we could have a good sight of various parameters in the patient's constriction, and in-depth analysis and exploration of this child. The diagnosis could be further guided by local hydrodynamic changes and the pattern of change in the coarctation pressure along with the course of the aortic arch in children. The rapid pressure decrease in the constricted segment because of the influence of the coarctation and the provision of its specific parameters are beneficial to our preoperative simulation of the surgical process of the constricted segment, to evaluate the feasibility of a certain surgical way for individual constriction, to evaluate whether the different postoperative hemodynamics are significantly alleviated, to achieve therapeutic purposes, and also to make a more systematic and comprehensive diagnosis of the disease.
However, this technology is in its infancy in the country and has seldom been applied to COA in the clinic, which is a new guide for future diagnosis and treatment of cardiovascular-related diseases. The current guideline diagnostic criteria are admittedly able to define the morphological and developmental "phenomenon" of aortic arch dysplasia, but the subject group hopes to elaborate on the physiological "nature" of aortic arch dysplasia from the hydrodynamic level. CFD has gradually evolved from a preclinical approach to a mode of consideration for human clinical applications, leading to a better understanding of the pathophysiology of the disease by mimicking blood flow-related processes, with significant effects on the formulation and modification of treatment options.