Ultrasound Particle Image Velocimetry to Investigate Potential Hemodynamic Causes of Limb Thrombosis After Endovascular Aneurysm Repair With the Anaconda Device

PURPOSE

To identify potential hemodynamic predictors for limb thrombosis (LT) following endovascular aneurysm repair with the Anaconda endograft in a patient-specific phantom.

MATERIALS AND METHODS

A thin-walled flow phantom, based on a patient's aortic anatomy and treated with an Anaconda endograft, that presented with a left-sided LT was fabricated. Contrast-enhanced ultrasound particle image velocimetry was performed to quantify time-resolved velocity fields. Measurements were performed in the same phantom with and without the Anaconda endograft, to investigate the impact of the endograft on the local flow fields. Hemodynamic parameters, namely vector complexity (VC) and residence time (RT), were calculated for both iliac arteries.

RESULTS

In both limbs, the vector fields were mostly unidirectional during the peak systolic and end-systolic velocity phases before and after endograft placement. Local vortical structures and complex flow fields were observed at the diastolic and transitional flow phases. The average VC was higher (0.11) in the phantom with endograft, compared to the phantom without endograft (0.05). Notably, in both left and right iliac arteries, the anterior wall regions corresponded to a 2- and 4-fold increase in VC in the phantom with endograft, respectively. RT simulations showed values of 1.3 to 6 seconds in the phantom without endograft. A higher RT (up to 25 seconds) was observed in the phantom with endograft, in which the left iliac artery, with LT in follow-up, showed 2 fluid stasis regions.

CONCLUSION

This in vitro study shows that unfavorable hemodynamics were present mostly in the limb that thrombosed during follow-up, with the highest VC and longest RT. These parameters might be valuable in predicting the occurrence of LT in the future.

CLINICAL IMPACT

This in-vitro study aimed to identify potential hemodynamic predictors for limb thrombosis following EVAR using ultrasound particle image velocimetry (echoPIV) technique. It was shown that unfavorable hemodynamic norms were present mostly in the thrombosed limb. Owing to the in-vivo feasibility of the echoPIV, future efforts should focus on the evaluation of these hemodynamic norms in clinical trials. Thereafter, using echoPIV as a bedside technique in hospitals becomes more promising. Performing echoPIV in pre-op phase may provide valuable insights for surgeons to enhance treatment planning. EchoPIV is also applicable for follow-up sessions to evaluate treatment progress and avoid/predict complications.

Systematic Review of the Current In Vitro Experience of the Endovascular Treatment of Juxtarenal Abdominal Aortic Aneurysms by Fenestrated and Parallel Endografting

OBJECTIVE

To identify and analyze the published in vitro benchtop experiments for the assessment of endovascular techniques used for the treatment of juxtarenal abdominal aortic aneurysms (jAAAs).

DATA SOURCES

Scopus, PubMed, and Web of Science.

REVIEW METHODS

A systematic literature search was carried out throughout March 2021 following PRISMA guidelines. Two investigators independently performed title and abstract screening to reveal all benchtop testing evaluating the endovascular treatment of jAAA.

RESULTS

A total of 19 studies were included, 8 evaluating fenestrated (FEVAR) and 11 parallel grafts (PGs). FEVAR studies used different custom testing apparatus (n=7) or 3D-printed models (n=1) to analyze dislodgement and migration resistance, misalignment consequences and causation, and bridging stents' radial force, flareability, fatigue, and fracture resistance. All PG studies used silicone-based models to analyze optimal oversizing, sealing length, gutter behavior, and possible reduction. Test evaluation in FEVAR in vitro testing was based on pullout force analysis (N=5), photo evaluation (n=1), fluoroscopy (n=1), X-rays (n=4), CT analysis (n=3), macro- and microscopic evaluation (n=4), water permeability (n=1), and fatigue simulator testing (n=1), while it was based on CT analysis in all PG studies adding ECG-gate in one study. The most frequently tested devices were Zenit (Cook) (n=7), Endurant (Medtronic) (n=5), and Excluder (Gore) (n=5) as main grafts, and Advanta V12 (n=14) as the bridging device.

CONCLUSIONS

This systematic review presents a broad analysis of the current in vitro methods evaluating the endovascular treatment of jAAA. Fundamental issues have been benchtop tested in both FEVAR and PGs. The analysis of the included studies allowed to recommend an optimal testing design. In vitro testing is a potential tool to further elucidate points of attention hard to investigate in vivo to finally enhance the endovascular treatment outcomes. Future in vitro studies are needed to evaluate the in vitro performance of all indistinctively used devices in the clinical practice.

Hemodynamic Comparison of Stent-Grafts for the Treatment of Aortoiliac Occlusive Disease

Purpose:

To compare the flow patterns and hemodynamics of the AFX stent-graft and the covered endovascular reconstruction of aortic bifurcation (CERAB) configuration using laser particle image velocimetry (PIV) experiments.

Materials and Methods:

Two anatomically realistic aortoiliac phantoms were constructed using polydimethylsiloxane polymer. An AFX stent-graft with a transparent cover made with a new method was inserted into one phantom. A CERAB configuration using Atrium’s Avanta V12 with transparent covers made with a previously established method was inserted into the other phantom, both modified stent-grafts were suitable for laser PIV, enabling visualization of the flow fields and quantification of time average wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT).

Results:

Disturbed flow was observed at the bifurcation region of the AFX, especially at the end systolic velocity (ESV) time-point where recirculation was noticeable due to vortical flow. In contrast, predominantly unidirectional flow was observed at the CERAB bifurcation. These observations were confirmed by the quantified hemodynamic results from PIV analysis where mean TAWSS of 0.078 Pa (range: 0.009–0.242 Pa) was significantly lower in AFX as compared with 0.229 Pa (range: 0.013–0.906 Pa) for CERAB (p<0.001). Mean OSI of 0.318 (range: 0.123–0.496) in AFX was significantly higher than 0.252 (range: 0.055–0.472) in CERAB (p<0.001). Likewise, mean RRT of 180 Pa−1 (range: 9–3603 Pa−1) in AFX was also significantly higher than 88 Pa−1 (range: 2–840 Pa−1) in CERAB (p=0.0086).

Conclusion:

In this in vitro study, the flow pattern of a modified AFX stent-graft was found to be more disturbed especially at the end systolic phase, its hemodynamic outcomes less desirable than CERAB configuration.

Clinical Relevance:

While the AFX stent-graft has an advantage over the CERAB configuration in eliminating radial mismatch, and maintaining the anatomical bifurcation for future endovascular intervention, this in vitro study revealed that the associated lower TAWSS, higher OSI and RRT may predispose to thrombosis and are, thus, less desirable as compared to a CERAB configuration. Further investigation is warranted to confirm whether these findings translate into the clinical setting.

Hemodynamic Comparison of Stent-Grafts for the Treatment of Aortoiliac Occlusive Disease

PURPOSE

To compare the flow patterns and hemodynamics of the AFX stent-graft and the covered endovascular reconstruction of aortic bifurcation (CERAB) configuration using laser particle image velocimetry (PIV) experiments.

MATERIALS AND METHODS

Two anatomically realistic aortoiliac phantoms were constructed using polydimethylsiloxane polymer. An AFX stent-graft with a transparent cover made with a new method was inserted into one phantom. A CERAB configuration using Atrium's Avanta V12 with transparent covers made with a previously established method was inserted into the other phantom, both modified stent-grafts were suitable for laser PIV, enabling visualization of the flow fields and quantification of time average wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT).

RESULTS

Disturbed flow was observed at the bifurcation region of the AFX, especially at the end systolic velocity (ESV) time-point where recirculation was noticeable due to vortical flow. In contrast, predominantly unidirectional flow was observed at the CERAB bifurcation. These observations were confirmed by the quantified hemodynamic results from PIV analysis where mean TAWSS of 0.078 Pa (range: 0.009-0.242 Pa) was significantly lower in AFX as compared with 0.229 Pa (range: 0.013-0.906 Pa) for CERAB (p<0.001). Mean OSI of 0.318 (range: 0.123-0.496) in AFX was significantly higher than 0.252 (range: 0.055-0.472) in CERAB (p<0.001). Likewise, mean RRT of 180 Pa^-1 (range: 9-3603 Pa^-1) in AFX was also significantly higher than 88 Pa^-1 (range: 2-840 Pa^-1) in CERAB (p=0.0086).

CONCLUSION

In this in vitro study, the flow pattern of a modified AFX stent-graft was found to be more disturbed especially at the end systolic phase, its hemodynamic outcomes less desirable than CERAB configuration.

CLINICAL RELEVANCE

While the AFX stent-graft has an advantage over the CERAB configuration in eliminating radial mismatch, and maintaining the anatomical bifurcation for future endovascular intervention, this in vitro study revealed that the associated lower TAWSS, higher OSI and RRT may predispose to thrombosis and are, thus, less desirable as compared to a CERAB configuration. Further investigation is warranted to confirm whether these findings translate into the clinical setting.