Analysis of Flow Through Extra-Anatomic Bypasses Between Supra-Aortic Branches Using Particle Image Velocimetry (PIV)

Abstract

Supra-aortic extra-anatomic debranch (SAD) are prosthetic surgical grafts used to revascularize head and neck arteries that would be blocked during a surgical or hybrid procedure used in treating ascending and arch of the aorta pathologies. However, bypassing the supra-aortic arteries but not occluding their orifice might introduce potential for competitive flow that reduces bypass patency. Competitive flow within the bypasses across the supra-aortic arteries has not previously been identified. This research identified haemodynamics due to prophylactic inclusion of bypasses from the brachiocephalic artery (BCA) to the left common carotid artery (LCCA), and from the LCCA to left subclavian artery (LSA). Four model configurations investigated the risk of competitive flow and the necessity of intentionally blocking the proximal LSA and/or LCCA. Particle image velocimetry (PIV) was used to assess haemodynamics in each model configuration. We found potential for competitive flow in the BCA-LCCA bypass when the LSA was blocked, in the LSA-LCCA bypass, when the LCCA alone or LCCA and LSA were blocked. Flow stagnated at the start of systole within the RCCA-LCCA bypass, along with notable recirculation zones and reciprocating flow occurring throughout systolic flow. Flow also stagnated in the LCCA-LSA bypass when the LCCA was blocked. There was a large recirculation in the LCCA-LSA bypass when both the LCCA and LSA were blocked. The presence of competitive flow in all other configurations indicated that it is necessary to block or ligate the native LCCA and LSA once the debranch is made and the thoracic endovascular aortic repair (TEVAR) completed.

Keywords: Cardiovascular surgery; debranching; haemodynamic modelling; particle image velocimetry.

Figure 1.

Extra-anatomic bypass example.

Figure 2.

Scaled in-vitro idealised geometry. All dimensions in mm except when specified.

Figure 3.

3D printed mould and resultant thin-walled silicone phantom.

Figure 4.

Silicone plug geometry.

Figure 5.

Model configurations (A) no blockages of any artery, (B) blocked flow to the LCCA, (C) blocked flow to the LSA and (D) blocked flow to both the LCCA and LSA.

Figure 6.

In vitro waveform for proximal aortic arch.

Figure 7.

The blue lines represent the fluid circuit. The red lines are the laser trigger and camera data cable. The orange circuit is the flowrate feedback loop. The components are: (A) reservoir, (B) in-line diaphragm pump, (C) piston pump, (D) flow straightener, (E) electromagnetic flowmeter, (F) Phantom model, (G) head tank, (H) overflow weir, (I) Nd:YAG laser, (J) camera, (K) data acquisition system and (L) DC power supply.

Figure 8.

Flowrate extraction locations: (1) the proximal arch, (2) the BCA, (3) the proximal LCCA, (4) the proximal LSA, (5) the BC bypass and (6) the CS bypass.

Figure 9.

Velocity vector map at peak systole (left) and respective systolic velocity profiles through the BC (middle) and CS bypasses (right) at the discrete timesteps ( $\tau$ 1- $\tau$ 7) for configurations (A) no blockages of any artery, (B) blocked flow to the LCCA, (C) blocked flow to the LSA and (D) blocked flow to both the LCCA and LSA. Note the different velocity scale across BC and CS bypasses.

Figure 10.

Flow through BC bypass during peak systole (τ1-τ4) for (A) configuration A and (B) configuration C.

Figure 11.

Flow through CS bypass during peak systole (τ1-τ4) for (A) configuration B and (B) configuration C.