Abstract
BackgroundThe purpose of this study was to investigate 3D flow patterns and vessel wall parameters in patients with dilated ascending aorta, age-matched subjects, and healthy volunteers.MethodsThoracic time-resolved 3D phase contrast CMR with 3-directional velocity encoding was applied to 33 patients with dilated ascending aorta (diameter ≥40 mm, age=60±16 years), 15 age-matched normal controls (diameter ≤37 mm, age=68±7.5 years) and 15 young healthy volunteers (diameter ≤30 mm, age=23±2 years). 3D blood flow was visualized and flow patterns were graded regarding presence of supra-physiologic-helix and vortex flow using a semi-quantitative 3-point grading scale. Blood flow velocities, regional wall shear stress (WSS), and oscillatory shear index (OSI) were quantified.ResultsIncidence and strength of supra-physiologic-helix and vortex flow in the ascending aorta (AAo) was significantly higher in patients with dilated AAo (16/33 and 31/33, grade 0.9±1.0 and 1.5±0.6) than in controls (2/15 and 7/15, grade 0.2 ± 0.6 and 0.6 ± 0.7, P<.05) or healthy volunteers (1/15 and 0/15, grade 0.1 ± 0.3 P<.05). Greater strength of the ascending aortic helix and vortex flow were associated with significant differences in AAo diameters (P<.05). Peak systolic WSS in the ascending aorta and aortic arch was significantly lower in patients with dilated AAo (P<.0157-.0488). AAo diameter positively correlated to time to peak systolic velocities (r=0.30-0.53, P<.04), OSI (r=0.33-0.49, P<0.02) and inversely correlated to peak systolic WSS (r=0.32-0.40, P<.03). Peak systolic WSS was significantly lower in AAo aneurysms at the right and outer curvature within the AAo and proximal arch (P<.01-.05).ConclusionsIncrease in AAo diameter is significantly correlated with the presence and strength of supra-physiologic-helix and vortex formation in the AAo, as well with decrease in systolic WSS and increase in OSI.
Highlights
The purpose of this study was to investigate 3D flow patterns and vessel wall parameters in patients with dilated ascending aorta, age-matched subjects, and healthy volunteers
The mean ascending aorta (AAo) diameter as well as the AAo/descending aorta (DAo) diameter ratio was significantly higher in the dilated AAo than in age-matched controls (P
As expected due to the physiological growth of the aorta with time [22], diameters of the AAo, aortic arch and DAo were significantly higher in the age-matched controls than in the healthy volunteers (P
Summary
The purpose of this study was to investigate 3D flow patterns and vessel wall parameters in patients with dilated ascending aorta, age-matched subjects, and healthy volunteers. Recent studies have focused on establishing alternative criteria for evaluating aneurysms, i.e. RNA expression patterns, biomarkers, aortic curvature geometry and mechanical properties of the aorta [1,5,6] In this context, the assessment of aortic hemodynamics and the presence of altered flow patterns, as well as distribution and changes in wall shear stress (WSS) and the oscillatory shear index (OSI) and their association with changes in aorta size may provide further insights in how aneurysms develop and in assessing the risk of dissection [7,8]. These factors may play an important role in aneurysm development and can be assessed by time-resolved 3D phase contrast cardiovascular magnetic resonance (CMR) with 3-directional velocity encoding (flow-sensitive 4D CMR), providing comprehensive information on aortic hemodynamics with 3D visualization of blood flow pattern [9,10,11]
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