Evaluation of aortic wall shear stress in patients with aortic dilatation

ABSTRACT Evaluation of Aortic Wall Shear Stress in Patients with Aortic Dilatation Objective: Aortic dilatation is a vascular pathology that often progresses asymptomatically but can lead to serious complications such as aneurysm and dissection. It has been reported that risk assessment based solely on aortic diameter is insufficient for predicting complications. This study aimed to investigate the prognostic value of wall shear stress (WSS) and flow patterns obtained from 4D cardiac magnetic resonance (CMR) imaging in asymptomatic patients with aortic dilatation detected by echocardiography. Methods: This single-centre, prospective, observational study included 33 patients diagnosed with ascending aortic dilatation by transthoracic echocardiography. All patients underwent two non-contrast 4D cardiac MRI scans approximately one year apart. Demographic data, comorbidities, laboratory results, medication use and left ventricular function were recorded. Aortic hemodynamic parameters and WSS were analysed using 4D flow MRI. Annual ascending aortic dilatation rate and WSS (maximum and mean) were calculated, and flow patterns were classified as laminar or non-laminar. The aortic wall was divided into 12 segments in the transverse plane and the segmental distribution of maximum WSS was assessed. Patients were categorized into two groups based on the presence or absence of rapid ascending aortic dilatation, and compared regarding WSS, flow pattern, left ventricular function, clinical-demographic features, and laboratory findings. Results: The average aortic dilatation rate over one year was 0.52 mm/year. No significant correlation was found between maximum and average WSS measurements and aortic dilatation rate. All patients with rapid aortic dilatation (n=5, 1.38±0.34 mm) had non-laminar flow patterns (100%) compared to only 35.7% in the non-rapid dilatation group (n=28, 0.37±0.30 mm), a statistically significant difference (p=0.008). No significant differences were found between the groups for maximum or mean WSS at either baseline or at follow-up, or for the annual change (∆) values (p>0.05). The most common location of maximum WSS was the 9th segment in both groups (80% vs. 46.4%), with no significant difference (p=0.497). In addition, no statistically significant differences in left ventricular function, comorbidities, demographics or laboratory parameters were observed (p>0.05). Conclusion: The aortic dilation rate was found to be significantly higher in patients exhibiting a non-laminar flow pattern, and we concluded that this flow type may be a risk indicator in terms of dilation rate. Keywords: 4D cardiac MRI, Aortic blood flow pattern, Ascending aortic dilatation, Wall shear stress