The washout characteristics of the aortic sinuses (AS) have been linked to the flow field in the aortic root (AR). This flow exhibits complex, unsteady structures that are dependent on valve type, AR morphology and physiological flow conditions past the aortic valve. Impaired AS washout increases the blood’s residence time, which can lead to complications, such as leaflet thrombosis.
This study presents the dynamic, full-volume washout characteristics of two aortic root morphologies studied in an in-vitro setup mimicking the left heart.
Two AR morphologies were investigated: a normal morphology and an enlarged root (figure 1). The morphologies are based on studies by Reul1 and Buellesfeld and Stortecky2.
An in-vitro setup (figure 2) produces physiological flow- and pressure profiles (5 L/min, 120/80 mmHg, 60 bpm). The setup is filled with blood analog fluid matching the blood’s viscosity and is used to investigate the AS washout at conditions resembling a human at rest
The ARs hold an Edwards Intuity valve with the leaflets oriented towards the AS.
A defined quantity of small Lagrangian tracer particles is locally injected into the AS and is allowed to distribute evenly.
A high-speed camera is used to record the tracer particles and to study the temporal reduction of their concentration over multiple cardiac cycles. This metric is directly related to the washout of the solid blood contents in the human aortic root.
Figure 3 shows snapshots of the particle washout for both AR morphologies during two consecutive cardiac cycles. The flow exhibited complex, unsteady and three-dimensional structures that drive the particle washout.
A composite image of the particle tracks (figure 4) reveals local regions of reduced flow. These regions are located close to the AS wall towards the base of AS. The large root showed a larger region of low flow indicating a somewhat less efficient particle washout at the base of the AS.
Quantitative data for the AS washout is given in figure 5 where the particle concentration normalized by its initial concentration is plotted over time (cardiac cycles).
The fastest washout dynamics were found during late systole while early systole and diastole showed very little washout. This manifests in high temporal concentration gradients during late systole and almost constant concentrations (“plateau”) during diastole and early systole.
The normal root exhibited higher temporal concentration gradients suggesting a more efficient washout in the first half of the cardiac cycle. Overall, a 73% washout per cycle was achieved and less than 10% of the particles remained in the AS after two cardiac cycles in both morphologies attesting good overall washout characteristics for both aortic roots. This is in good agreement with previous washout studies, e.g. by Midha3.
Discussion and concluding remarks
High-speed imaging of locally injected Lagrangian tracer particles made it possible to study the detailed, volumetric dynamics of AS washout and the influence of the AR morphology.
Complex three-dimensional flow structures were seen in the AS that drive the washout
The enlarged AR exhibited a slower late-systolic washout and a larger low-flow region at the base of the AS. The normal AR showed faster and more efficient washout dynamics.