False lumen fluid dynamics and biomechanics by 4D flow CMR and their relationship with aortic growth rate and partial false lumen thrombosis in chronic aortic dissection of the descending aorta

Abstract

Background: Predictors of aortic dilation or adverse events in patients with a false lumen in the descending aorta after an acute aortic dissection (AD) have mostly been focused on morphological or anatomical variables. Although the presence of flow in the false lumen has been associated with adverse outcomes, studies quantifying flow dynamics in the false lumen and its relationship with aortic growth rate are still limited. On the other hand, partial thrombosis of the false lumen has recently been associated with poor outcomes. Meanwhile, the fluid dynamic and biomechanical characteristics associated with partial thrombosis remain to be elucidated. Aims: (i) To assess whether false lumen fluid dynamic and biomechanical descriptors are prognostic determinants of aortic growth rate in patients with chronic AD of the descending aorta, and (ii) to analyze the association between these descriptors and the presence and extent of thrombus in the false lumen. Materials and Methods: Patients with a chronic non-thrombosed or partiallythrombosed false lumen in the descending aorta after an AD and no genetic connective tissue disorders underwent an imaging follow-up including a contrast-enhanced 4D flow cardiovascular magnetic resonance (CMR) protocol and consecutive computed tomography angiograms (CTA) acquired at least 1 year apart. A comprehensive analysis of anatomical features (including quantification of thrombus extent), and false lumen fluid dynamics (rotational flow, wall shear stress, flow energy and intensity) and biomechanics (pulse wave velocity) was performed. Results: Sixty-eight patients with a chronic, false lumen in the descending aorta were included (35 surgically-treated type A AD with residual tear and 19 medically-treated type B AD). However, to determine prognostic factors for aortic growth rate, a subgroup of 54 patients who had undergone two consecutive CTA was considered. Median follow-up duration was 40 months. The in-plane rotational flow, pulse wave velocity and the percentage of thrombus in the false lumen were positively related to aortic growth rate (p=0.006, 0.017 and 0.037, respectively), whereas wall shear stress showed a nearly-significant positive association (p=0.060). These results were found irrespectively of the type of AD. On the other hand, in the analysis testing flow and biomechanical descriptors related to partial thrombosis of the false lumen, the complete study cohort (68 patients) was included. The aortic growth rate was higher in the presence of partial thrombosis (33 patients) than in the case of no thrombosis (35 patients) in the false lumen (1.6 [0.8 -3.3] vs. 1.0 [0.5 - 1.8] mm/year, respectively). In multivariate logistic regression false lumen kinetic energy (p=0.038) discriminated patients with partial false lumen thrombosis from patients with no thrombosis. Similarly, in separated multivariate linear correlations, kinetic energy (p=0.006) and false lumen inflow (p=0.002) were independently related to the extent of the thrombus. False lumen vortexes, flow acceleration and stasis, wall shear stress and pulse wave velocity showed limited associations with thrombus presence and extent. Conclusions: Rotational flow, pulse wave velocity, and wall shear stress are positively related to aortic growth rate, and should be implemented in the follow-up algorithm of patients with a chronic, non-thrombosed or partially-thrombosed false lumen in the descending aorta. Furthermore, this work provided evidence, for the first time, that in these patients, false lumen hemodynamic parameters, especially kinetic energy, are closely linked with the presence and extent of false lumen thrombosis, and that these non-invasive measures might be important in patient management. Nonetheless, further prospective studies areneeded to confirm if the assessment of these parameters may help to identify patients at higher risk of adverse clinical events.

Date of Award	20 Nov 2023
Original language	English
Supervisor	Jose Fernando Rodriguez Palomares (Director) & Artur Evangelista Masip (Director)