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Author Spotlight: Using Point-of-Care Ultrasound for Comprehensive Evaluation of the Abdominal Aorta
Published on: September 8, 2023
Multi-modality image-based computational analysis of haemodynamics in aortic dissection
Desmond Dillon-Murphy1, Alia Noorani1, David Nordsletten1
1Department of Biomedical Engineering, King's College London, London, SE1 7EH, UK.
Insights
Aortic dissection alters blood flow dynamics, increasing pressure and wall stress, particularly in the true lumen. Computational models reveal dissection significantly increases left ventricular workload and impacts outcomes based on tear configurations.
Area of Science:
- Cardiovascular Science
- Biomedical Engineering
- Medical Imaging
Background:
- Aortic dissection involves a tear in the aorta, creating true and false lumens separated by an intimal flap.
- Stable type B aortic dissections present a debate regarding the optimal timing for surgical intervention.
- Understanding aortic dissection hemodynamics is crucial for predicting patient outcomes.
Purpose of the Study:
- To investigate the complex hemodynamics within aortic dissections using medical imaging and computational fluid dynamics (CFD).
- To analyze the impact of morphometric variations, such as septum removal and connecting tear numbers, on aortic blood flow.
- To compare hemodynamics in dissected aortas with a simulated healthy aorta.
Main Methods:
- Creation of patient-specific CFD models of acute Stanford type B aortic dissection.
- Utilized 2D and 4D Phase-Contrast Magnetic Resonance Imaging (PC-MRI) for patient-specific flow data and model validation.
- Incorporated zero-dimensional Windkessel models for distal vasculature and a lumped-parameter heart model.
Main Results:
- Identified localized increases in velocity, pressure, and wall shear stress in the narrow true lumen and near entry tears.
- Demonstrated a significant increase in left ventricular stroke work (estimated 14%) due to aortic dissection.
- Showed that the absence of secondary connecting tears led to substantial hemodynamic changes, including increased true lumen flow and decreased peak pressure.
Conclusions:
- Computational modeling provides valuable insights into the intricate hemodynamics of aortic dissection.
- Hemodynamic alterations in dissection significantly affect cardiac workload and may influence long-term outcomes.
- The number and configuration of connecting tears play a critical role in modifying flow patterns and pressures within the dissected aorta.
Abstract:
Aortic dissection is a disease whereby an injury in the wall of the aorta leads to the creation of a true lumen and a false lumen separated by an intimal flap which may contain multiple communicating tears between the lumina. It has a high associated morbidity and mortality, but at present, the timing of surgical intervention for stable type B dissections remains an area of debate. Detailed knowledge of haemodynamics may yield greater insight into the long-term outcomes for dissection patients by providing a greater understanding of pressures, wall shear stress and velocities in and around the dissection. In this paper, we aim to gather further insight into the complex haemodynamics in aortic dissection using medical imaging and computational fluid dynamics modelling. Towards this end, several computer models of the aorta of a patient presenting with an acute Stanford type B dissection were created whereby morphometric parameters related to the dissection septum were altered, such as removal of the septum, and the variation of the number of connecting tears between the lumina. Patient-specific flow data acquired using 2D PC-MRI in the ascending aorta were used to set the inflow boundary condition. Coupled zero-dimensional (Windkessel) models representing the distal vasculature were used to define the outlet boundary conditions and tuned to match 2D PC-MRI flow data acquired in the descending aorta. Haemodynamics in the dissected aorta were compared to those in an equivalent 'healthy aorta', created by virtually removing the intimal flap (septum). Local regions of increased velocity, pressure, wall shear stress and alterations in flow distribution were noted, particularly in the narrow true lumen and around the primary entry tear. The computed flow patterns compared favourably with those obtained using 4D PC-MRI. A lumped-parameter heart model was subsequently used to show that in this case there was an estimated 14 % increase in left ventricular stroke work with the onset of dissection. Finally, the effect of secondary connecting tears (i.e. those excluding the primary entry and exit tears) was also studied, revealing significant haemodynamic changes when no secondary tears are included in the model, particularly in the true lumen where increases in flow over [Formula: see text] and drops in peak pressure of 18 % were observed.
