Precise plan of hybrid treatment for thoracoabdominal aortic aneurysm: Hemodynamics of retrograde reconstruction visceral arteries from the iliac artery

Hemodynamic analysis of hybrid treatment for thoracoabdominal aortic aneurysm based on Newtonian and non-Newtonian models in a patient-specific model

The accuracy of the Newtonian model used in retrograde visceral revascularization (RVR) of hybrid surgery for thoracoabdominal aortic aneurysm (TAAA) hemodynamic simulation remains unclear. Noting that an appropriate blood viscosity model is a significant factor to capture hemodynamic changes in numerical studies. Therefore, both Newtonian and non-Newtonian blood viscosity models were adopted in this study to investigate the importance of hemodynamics when non-Newtonian blood property was accounted for in a patient-specific RVR simulation. The results revealed that disturbed flow and unfavorable WSS distribution can be observed in the anastomosis region under both blood viscosity models due to the retrograde flow pattern in the RVR model. However, although the non-Newtonian blood model has negligible effect on flow pattern and pressure drop, there were of significance quantitative and qualitative difference of local normalized helicity and wall shear stress distribution under pulsatile flow condition. In particular, the unfavorable WSS indicators distribution was better matched with a patient-specific follow-up report when non-Newtonian blood viscosity was accounted for. To conclude, the use of a Newtonian blood model is a reasonable approximation to obtain the general features of the flow field under steady flow condition. However, to study the hemodynamic parameters within retrograde flow under pulsatile flow condition, a non-Newtonian model may be more appropriate.

Single Stem Visceral Debranching for Complex Aortic Disease

Objective

The treatment of complex aortic disease has been described with various retrograde visceral bypass techniques. An original technique with a single stem retrograde visceral graft (SSRVG) is presented.

Methods

This was a single centre retrospective study including 16 patients between 2015 and 2019. Patients were treated for aortic dissection (AD; type A and acute or chronic type B), thoraco-abdominal aortic aneurysms (TAAAs), and visceral occlusive disease. Surgery consisted of visceral vessel debranching from the native infrarenal aorta or from an aortic graft. In the case of AD, surgical fenestration was performed. Additional thoracic endovascular aneurysm repair (TEVAR) completed the treatment when indicated, during the same procedure or later. Patient outcomes and reconstruction patency were studied.

Results

The mean patient age was 64 years (median 68 ± 12.6). Ten (62%) patients were treated for AD, three (19%) for TAAA, and three (19%) for occlusive disease. Sixty-nine target vessels were debranched with this SSRVG technique. Aortic surgical fenestration was performed in eight cases and TEVAR in four. During their hospital stay, three (19%) TAAA patients died, seven cases of renal insufficiency (44%), four cases of pneumonia (25%), and three colonic ischaemia cases (19%) were noted. After a mean follow up of 21 months, no other deaths occurred. All vessels (except two inferior mesenteric arteries) were patent and no endoleak was noted.

Conclusion

The SSRVG technique can be offered in various complex aortic diseases. The use of a single graft is feasible and reduces the volume of multiple branch assembly in the retroperitoneal space. The observed patency rate is high.

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Not all patients with complex aortic disease are amenable to open surgery or total endovascular repair.

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Hybrid surgery with visceral vessel debranching may represent an alternative.

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Various techniques using several grafts to debranch visceral vessels have been published.

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The use of a single conduit for total visceral debranching is relatively straightforward and provides excellent patency results.

Effect of Anastomosis Angles on Retrograde Perfusion and Hemodynamics of Hybrid Treatment for Thoracoabdominal Aortic Aneurysm

BACKGROUND

Hemodynamic effects on the retrograde visceral reconstruction (RVR) for thoracoabdominal aortic aneurysms treatment by anastomotic angle remains unclear. This study aims to qualitatively and quantitatively investigate the effects of different anastomotic angles on hemodynamics and patency.

METHODS

Three RVR models with 45°, 60° and 90° anastomotic angles were reconstructed respectively by manipulating apostoperative patient-specific model. The manipulated models of the RVRs were numerically simulated and analyzed in terms of hemodynamics including theinstant and cumulative patency, flow pattern and indicators based on wall shear stress (WSS).

RESULTS

Although a smaller anastomotic angle may decrease the patency rate of common iliac arteries, it can improve the visceral perfusion during a cardiac cycle. More importantly, RVR with the smallest anastomotic angle experienced a minimal low time-averaged wall shear stress, high oscillatory shear index and relative residence time in the anastomosis region, whereas the largest anastomotic angle can introduce more unfavorable WSS in the graft trunk. Furthermore, a spiral flow pattern was observed in the proximal graft trunk of all three models, where no high-risk shear distribution was detected in this region.

CONCLUSION

A smaller anastomotic angle may have more benefits of hemodynamic environment in RVR, especially the WSS distribution and flow pattern in the graft trunk. We may also suggest that additional stents or an extended cuff for the graft can be used to induce spiral flow intentionally, which can further improve local hemodynamic environment and long-term prognosis.

[Visceral debranching in hybrid surgery of thoracoabdominal aortic aneurysms]

Presented herein is a review of the literature dedicated to the method of visceral debranching, i. e., switching of the visceral and renal branches of the abdominal aorta to its intact portion, using synthetic vascular prostheses as the first stage of hybrid surgical treatment of thoracoabdominal aortic aneurysms prior to endovascular aortic aneurysm repair. This is accompanied and followed by describing the history of the problem, operative technique, results of studies, as well as the data from registries and meta-analyses. Also discussed are the main complications of the method and measures of their prevention. We conclude that hybrid surgery of the thoracoabdominal portion of the aorta is a promising method in a particular cohort of patients, especially those at high surgical risk of 'open' aortic surgery.