Haemodynamics of Different Configurations of a Left Subclavian Artery Stent Graft for Thoracic Endovascular Aortic Repair

Hemodynamics of different configurations of the left subclavian artery parallel stent graft for thoracic endovascular aortic repair

BACKGROUND AND OBJECTIVE

Parallel (chimney and periscope) graft technique is an effective approach for left subclavian artery (LSA) reconstruction in patients treated by thoracic endovascular aortic repair (TEVAR) for the inadequate landing zone. However, certain stent graft (SG) configurations may promote thrombosis and reduce distal blood flow, increasing risks of cerebral infarction and reintervention.

METHODS

In this paper, we first attempt to systematically evaluate the hemodynamic performances of different parallel graft techniques as potential determinants of complication risks. Based on the patient-specific 3D aortic geometry undergoing parallel graft technique, fifteen models in total for five kinds of LSA branched SG configurations (Forward, Backward, Extended, Elliptical and Periscopic) were designed virtually, and the hemodynamic discrepancies between them were analyzed by computational fluid dynamics.

RESULTS

Results show that flow rate of patients undergoing periscope technique reduces by half compared with chimney technique, suggesting that periscope SG may cause more serious flow obstruction to LSA, leading to stroke. For chimney stent structure, the extension length 0has little influence on energy loss and other parameters. Conversely, hemodynamic differences between the retrograde curvature and the antegrade curvature are significant (time average WSS: 47.07%), so the retrograde curvature might prompt SG displacement. Furthermore, the flatter chimney SG induces more aggressive hemodynamic forces, among which the difference of the maximum WSS between the flatter SG and nearly round SG reaches 65.56%, leading to the greater risk of vascular wall damage.

CONCLUSIONS

Results obtained might provide suggestions for physicians to formulate appropriate parallel graft technique schemes in TEVAR.

Computational study of fenestration and parallel grafts used in TEVAR of aortic arch aneurysms

To explore the differences between fenestration technique and parallel grafts technique of thoracic endovascular aortic repair, and evaluate the risk of complications after interventional treatment of aortic arch aneurysms. A three-dimensional aortic model was established from the follow-up imaging data of patient who reconstructed the superior arch vessel by the chimney technique, which was called the chimney model. Based on the chimney model, the geometric of the reconstructed vessel was modified by virtual surgery, and the normal model, fenestration model and periscope model were established. The blood flow waveforms measured by 2D phase contrast magnetic resonance imaging were processed as the boundary conditions of the ascending aorta inlet and the superior arch vessels outlets of the normal model. The pressure waveform of descending aorta was obtained using three-element Windkessel model, and specific pressure boundary conditions were imposed at reconstructed branches for the postoperative models. Through computational fluid dynamics simulations, the hemodynamic parameters of each model were obtained. The reconstructed vessel flow rate of the periscope model and the fenestration model are 33% and 50% of that of the normal model, respectively. The pressure difference between the inner and outer walls of the fenestration stent and periscope stent is 3.15 times and 7.56 times that of the chimney stent. The velocity in the fenestration stent and periscope stent is uneven. The high relative residence time is concentrated in the region around the branch stents, which is prone to thrombosis. The "gutter" part of the chimney model may become larger due to the effect of the stent-graft DF, increasing the risk of endoleak. For patients with incomplete circle of Willis, the periscope technique to reconstruct the supra-arch vessels may affect blood perfusion. It is recommended to use balloon-expandable stent for fenestration stent and periscope stent, and self-expanding stent for chimney stent. For patients with aortic arch aneurysms, the fenestration technique may be superior to the parallel grafts technique.

Safety and Efficacy of Inner Branched Stent-Graft in the Treatment of Aortic Arch Disease: A Systematic Review

OBJECTIVE

To provide a descriptive overview on the contemporary outcomes of thoracic endovascular arch repair with inner branched endoprosthesis (bTEVAR) for the treatment of aortic arch pathologies.

METHODS

A comprehensive literature search was performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Pre-defined search terms were used to interrogate PubMed and OVID Medline databases from January 1999 to July 2022. Patient characteristics, indication for treatment, procedural data, mortality rates, postoperative complications, and reintervention rate during follow-up were evaluated.

RESULTS

Nineteen articles were included, encompassing a total of 618 patients who received bTEVAR, most of which were double-branched (63.9%, n=395). The main indication for treatment was aneurysm secondary to chronic aortic dissection (38.8%, n=240/618) with a mean maximum diameter of 58.3±11.4 mm. Pooled mean technical success rate was 97.4±4.4% (95% confidence interval [CI]=95.1%-99.5%); 2 and 3 patients required conversion to chimney technique and open repair, respectively. Among the pooled rates of early complications, postoperative stroke was the highest (10.5%; 95% CI=6.8%-14.3%). Thirty-day and in-hospital mortality rate was 5.5% (95% CI=2.6%-9.7%). Forty patients (6.5%; 95% CI=2.5%-9.5%) required early reintervention. During a mean follow-up of 20.7±13.5 months, the mortality rate was 18.2% (n=108/593; 95% CI=8.6%-20.6%) where 12 (11.1%) were aortic-related. Pooled late reintervention rate was 9.6% (95% CI=4.8%-14.3%). Comparison of demographics and outcomes found no significant difference between single and double bTEVAR.

CONCLUSION

Branched thoracic endovascular aortic repair is a promising approach for aortic arch pathologies with a high technical success rate despite a steep learning curve. However, contemporary outcomes reflect that postoperative stroke remains the predominant concern. Further experience and long-term follow-up are required to sufficiently elucidate the safety and durability of bTEVAR in the management of aortic pathologies for high-risk patients.

CLINICAL IMPACT

This systematic review summarized the contemporary outcomes of thoracic endovascular aortic repair with different inner branched stent-grafts for the management of aortic arch pathologies. Pooled results from nineteen studies with 618 patients demonstrated a high technical success rate and an acceptable mortality rate. However, postoperative stroke remains the major concern. Long-term follow-up is needed to evaluate its durability.

Near-wall hemodynamic changes in subclavian artery perfusion induced by retrograde inner branched thoracic endograft implantation

Objective

Left subclavian artery (LSA)-branched endografts with retrograde inner branch configuration (thoracic branch endoprosthesis [TBE]) offer a complete endovascular solution when LSA preservation is required during zone 2 thoracic endovascular aortic repair. However, the hemodynamic consequences of the TBE have not been well-investigated. We compared near-wall hemodynamic parameters before and after the TBE implantation using computational fluid dynamic simulations.

Methods

Eleven patients who had undergone TBE implantation were included. Three-dimensional aortic arch geometries were constructed from the pre- and post-TBE implantation computed tomography images. The resulting 22 three-dimensional aortic arch geometries were then discretized into finite element meshes for computational fluid dynamic simulations. Inflow boundary conditions were prescribed using normal physiological pulsatile circulation. Outlet boundary conditions consisted of Windkessel models with previously published values. Blood flow, modeled as Newtonian fluid, simulations were performed with rigid wall assumptions using SimVascular's incompressible Navier-Stokes solver. We compared well-established hemodynamic descriptors: pressure, flow rate, time-averaged wall shear stress (TAWSS), the oscillatory shear index (OSI), and percent area with an OSI of >0.2. Data were presented on the stented portion of the LSA.

Results

TBE implantation was associated with a small decrease in peak LSA pressure (153 mm Hg; interquartile range [IQR], 151-154 mm Hg vs 159 mm Hg; IQR, 158-160 mm Hg; P = .005). No difference was observed in peak LSA flow rates before and after implantation: 40.4 cm³/ (IQR, 39.5-41.6 cm³/s) vs 41.3 cm³/s (IQR, 37.2-44.8 cm³/s; P = .59). There was a significant postimplantation increase in TAWSS (15.2 dynes/cm² [IQR, 12.2-17.7 dynes/cm²] vs 6.2 dynes/cm² [IQR, 5.7-10.3 dynes/cm²]; P = .003), leading to decreases in both the OSI (0.088 [IQR, 0.063 to -0.099] vs 0.1 [IQR, 0.096-0.16]; P = .03) and percentage of area with an OSI of >0.2 (10.4 [IQR, 5.8-15.8] vs 15.7 [IQR, 10.7-31.9]; P = .13). Neither LSA side branch angulation (median, 81°, IQR, 77°-109°) nor moderate compression (16%-58%) seemed to have an impact on the pressure, flow rate, TAWSS, or percentage of area with an OSI of >0.2 in the stented LSA.

Conclusions

The implantation of TBE produces modest hemodynamic disturbances that are unlikely to result in clinically relevant changes.

Non-invasive estimation of the parameters of a three-element windkessel model of aortic arch arteries in patients undergoing thoracic endovascular aortic repair

Background: Image-based computational hemodynamic modeling and simulations are important for personalized diagnosis and treatment of cardiovascular diseases. However, the required patient-specific boundary conditions are often not available and need to be estimated. Methods: We propose a pipeline for estimating the parameters of the popular three-element Windkessel (WK3) models (a proximal resistor in series with a parallel combination of a distal resistor and a capacitor) of the aortic arch arteries in patients receiving thoracic endovascular aortic repair of aneurysms. Pre-operative and post-operative 1-week duplex ultrasound scans were performed to obtain blood flow rates, and intra-operative pressure measurements were also performed invasively using a pressure transducer pre- and post-stent graft deployment in arch arteries. The patient-specific WK3 model parameters were derived from the flow rate and pressure waveforms using an optimization algorithm reducing the error between simulated and measured pressure data. The resistors were normalized by total resistance, and the capacitor was normalized by total resistance and heart rate. The normalized WK3 parameters can be combined with readily available vessel diameter, brachial blood pressure, and heart rate data to estimate WK3 parameters of other patients non-invasively. Results: Ten patients were studied. The medians (interquartile range) of the normalized proximal resistor, distal resistor, and capacitor parameters are 0.10 (0.07-0.15), 0.90 (0.84-0.93), and 0.46 (0.33-0.58), respectively, for common carotid artery; 0.03 (0.02-0.04), 0.97 (0.96-0.98), and 1.91 (1.63-2.26) for subclavian artery; 0.18 (0.08-0.41), 0.82 (0.59-0.92), and 0.47 (0.32-0.85) for vertebral artery. The estimated pressure showed fairly high tolerance to patient-specific inlet flow rate waveforms using the WK3 parameters estimated from the medians of the normalized parameters. Conclusion: When patient-specific outflow boundary conditions are not available, our proposed pipeline can be used to estimate the WK3 parameters of arch arteries.

In-vitro and In-silico Haemodynamic Analyses of a Novel Embedded Iliac Branch Device

Background

Iliac branch devices (IBDs) are valid tools for internal iliac artery preservation during endovascular abdominal aortic aneurysm and iliac aneurysm repair. The purpose of this study was to evaluate the effectiveness of a novel IBD with an embedded branch configuration.

Method

A typical iliac artery model was reconstructed, and two models were manufactured using three-dimensional printing technology. The novel IBD was deployed into one iliac artery model by an experienced vascular surgeon. A mock circulation loop (MCL) and a computational fluid dynamics (CFD) simulation were used to investigate the haemodynamic parameters of the iliac models without (Model A) and with (Model B) the IBD. A morphological analysis was conducted using computed tomography angiography and medical endoscopy. The flow distribution rate (FDR) and energy loss (EL) were used to quantify IBD performance.

Results

The FDR of the right internal iliac artery in the MCL of Model A and Model B was 18.88 ± 0.12% and 16.26 ± 0.09%, respectively (P = 0.0013). The FDR of the right internal iliac artery in the CFD simulation of Model A and Model B was 17.52 and 14.49%, respectively. The EL of Model A was greater than Model B in both the MCL and the CFD simulation. Compared with Model A, Model B had a larger region (8.46 vs. 3.64%) with a relative residence time of >20 Pa⁻¹ at peak systole. Meanwhile, the area where the oscillatory flow index was >0.4 was significantly smaller in Model B than in Model A (0.46 vs. 0.043%). The region with an average wall shear stress of >4 Pa was greater in Model B than in Model A (0 vs. 0.22%).

Conclusion

The MCL and CFD simulation showed that the novel IBD had little impact on the FDR and EL of the iliac artery models. However, the IBD might be an effective tool for the treatment of abdominal aortic/iliac aneurysms that extend into branches. Further investigations are warranted to confirm whether this IBD could be useful in the clinic.

Hemodynamic Parameters Predict In-stent Thrombosis After Multibranched Endovascular Repair of Complex Abdominal Aortic Aneurysms: A Retrospective Study of Branched Stent-Graft Thrombosis

Background: Branch vessel occlusion is reported in endovascular repair of aortic pathology. This study aimed to evaluate the hemodynamic indicators associated with in-stent thrombosis (IST) of a branched stent-graft (BSG) after endovascular aortic repair (EVAR) of a complex abdominal aortic aneurysm.

Methods: A retrospective evaluation was performed based on the computed tomography (CT) scans and clinical data of three patients who underwent multi-branched endovascular repair. Patient-specific 3-dimensional models were reconstructed, and hemodynamic analysis was performed for IST. Hemodynamics-related parameters including time-averaged wall shear stress (TAWSS), oscillatory shear stress index (OSI), and relative residence time (RRT) were compared among the individual patients.

Results: The flow velocity, TAWSS, OSI, and RRT were radically changed in the area of the IST. In BSGs, IST tended to occur in the regions of hemodynamic alteration near the bends in the device, where a decreased flow velocity (<0.6 m/s) and TAWSS (<0.8 Pa) and an elevated OSI (>0.2) and RRT (>5 s) were consistently observed.

Conclusions: Hemodynamic perturbations in BSGs cause a predisposition to IST, which can be predicted by a series of changes in the flow parameters. Early hemodynamic analysis might be useful for identifying and remediating IST after multibranched endovascular repair.

Efficiently Simulating an Endograft Deployment: A Methodology for Detailed CFD Analyses

Numerical models of endografts for the simulation of endovascular aneurysm repair are increasingly important in the improvement of device designs and patient outcomes. Nevertheless, current finite element analysis (FEA) models of complete endograft devices come at a high computational cost, requiring days of runtime, therefore restricting their applicability. In the current study, an efficient FEA model of the Anaconda™ endograft (Terumo Aortic, UK) was developed, able to yield results in just over 4 h, an order of magnitude less than similar models found in the literature. The model was used to replicate a physical device that was deployed in a 3D printed aorta and comparison of the two shapes illustrated a less than 5 mm placement error of the model in the regions of interest, consistent with other more computationally intensive models in the literature. Furthermore, the final goal of the study was to utilize the deployed fabric model in a hemodynamic analysis that would incorporate realistic fabric folds, a feature that is almost always omitted in similar simulations. By successfully exporting the deployed graft geometry into a flow analysis, it was illustrated that the inclusion of fabric wrinkles enabled clinically significant flow patterns such as flow stagnation and recirculation to be detected, paving the way for this modelling methodology to be used in future for stent design optimisation.