A concept of aortic hot spot detection: there is still a job for the engineer

Abstract

The authors' concept and approach to aorta modelling, and the very idea of the present study, are undoubtedly interesting and deserve detailed consideration [1]. The flow structure through the aorta and its branches, high flow velocity areas and wall stress peaks in such a complex vascular formation as the aorta have always been and still remain useful data that the surgeon needs when preparing for aortic replacement. Evidence of haemodynamically adverse flow areas and wall stress sites are of prime interest in order to determine the location of the aortotomy for proximal anastomosis. The concept of the present study is critically important as we really need to know the areas of flow disturbances - as the authors call them. They proposed that an anastomosis should be placed in relatively safe flow areas: outside those of peak flow velocities and wall stress areas. It is quite right. The anastomosis per se might provoke aorta wall dissection and aneurysm formation. A juncture of two different materials in the site of the aortic graft is bound to cause the flow to slow down and wall stress to grow. And what contributes to increased complexity is that the anastomosis might trigger off disruption of endothelium layer continuum and intimal hyperplasia development. The fibrous tissue of anastomosis, when placed at a right, rather than an oblique angle to the flow field, may cause the aorta lumen to narrow as a patient grows up. The authors showed how their concept worked by using computational fluid dynamic (CFD) evaluation. They emphasized that their method aimed to identify patient-specific aortic flow before surgery. This is a good point about their research strategy. In their model for CFD-evaluation, the authors made a series of assumptions to address flow equations and they had to depart from the true anatomic configuration of aorta. The authors' final choice was a model of a constant cross-section aorta with a direct and steady flow. This might not be critical for demonstrating the concept. Yet, any simplification of the model results in a loss of the required accuracy. One should be aware of the necessity of obtaining the reliable hot spots location data in the patient's aorta preoperatively. We would like to invite the authors - engineers, in the first place - to continue their efforts (and we invite surgeons and other researchers to join in) to develop a sustainable model of the aortic arch and aortic flow. The development of such a model could build on the most common aortic arch patterns found in humans as well as the anomalies of aortic arch [2]. In actual fact, there should be a few models. The choice could be narrowed down to two or even three models. We assume the key to the problem is how variability of flow patterns, dimensions, and configurations of aorta might be incorporated into the model. Lastly, dimensions of the model should be based on a correlation analysis between the dimensions of the aorta and parameters of patient's bodily growth. Conflict of interest: none declared.