Abstract
Aortic wall stiffness, tear size and location and the presence of abdominal side branches arising from the false lumen (FL) are key properties potentially involved in FL enlargement in chronic aortic dissections (ADs). We hypothesize that temporal variations on FL flow patterns, as measured in a cross-section by phase-contrast magnetic resonance imaging (PC-MRI), could be used to infer integrated information on these features. In 33 patients with chronic descending AD, instantaneous flow profiles were quantified in the FL at diaphragm level by PC-MRI. We used a lumped-parameter model to assess the changes in flow profiles induced by wall stiffness, tear size/location, and the presence of abdominal side branches arising from the FL. Four characteristic FL flow patterns were identified in 31/33 patients (94%) based on the direction of flow in systole and diastole: BA = systolic biphasic flow and primarily diastolic antegrade flow (n = 6); BR = systolic biphasic flow and primarily diastolic retrograde flow (n = 14); MA = systolic monophasic flow and primarily diastolic antegrade flow (n = 9); MR = systolic monophasic flow and primarily diastolic retrograde flow (n = 2). In the computational model, the temporal variation of flow directions within the FL was highly dependent on the position of assessment along the aorta. FL flow patterns (especially at the level of the diaphragm) showed their characteristic patterns due to variations in the cumulative size and the spatial distribution of the communicating tears, and the incidence of visceral side branches originating from the FL. Changes in wall stiffness did not change the temporal variation of the flows whereas it importantly determined intraluminal pressures. FL flow patterns implicitly codify morphological information on key determinants of aortic expansion in ADs. This data might be taken into consideration in the imaging protocol to define the predictive value of FL flows.
Highlights
Aortic dissection (AD) is a life-threatening condition
Based on the direction of flow in systole and diastole, we could identify 4 characteristic false lumen (FL) flow patterns in our population where representative cases are depicted in Fig 1: BA = systolic biphasic flow and primarily diastolic antegrade flow in 6 patients (18%); BR = systolic biphasic flow and primarily diastolic retrograde flow in 14 patients (42%); MA = systolic monophasic flow and primarily diastolic antegrade flow in 9 patients (27%); and MR = systolic monophasic flow and primarily diastolic retrograde flow in 2 patients (6%)
At the thoracic aorta (ThAo), flows were predominantly antegrade in systole and retrograde in diastole, while they inverted when approaching the distal tear, where they were mainly retrograde in systole and antegrade in diastole
Summary
Modifiable morphological parameters, such as a large interluminal communicative area [2,3] and incidence of visceral arteries arising from the FL [4]; and non-modifiable biomechanical features, such as aortic wall stiffness [4]; have been suggested as predictor of progressive aortic dilatation. Many of these parameters are difficult to measure with the limitation of the available imaging techniques plus different techniques provide inconsistencies between measurements. Little remains known on the determinants and relevance of these flow pattern differences in chronic ADs as well as how these can/should be studied with imaging
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