Hemodynamics study of a multilayer stent for the treatment of aneurysms

Long-term outcome of multilayer flow modulator in aortic aneurysms

BACKGROUND

This retrospective study investigated the efficacy of endovascular treatment with multilayer flow modulators (MFMs) for treating aortic aneurysms in high-risk patients unsuitable for conventional treatments.

PATIENTS AND METHODS

Conducted from 2011 to 2019 at a single center, this retrospective observational study included 17 patients who underwent endovascular treatment with MFMs. These patients were selected based on their unsuitability for traditional surgical or endovascular procedures. The study involved meticulous pre-procedural planning, precise implantation of MFMs, and follow-up using CT angiography. The primary focus was on volumetric and flow volume changes in aneurysms, along with traditional diameter measurements. Moreover, the technical success and post-procedural complications were also registered.

RESULTS

The technical success rate was 100%, and 30-day procedural complication rate was 17.6%. Post-treatment assessments revealed that 11 out of 17 patients showed a decrease in flow volume within the aneurysm sac, indicative of a favorable hemodynamic response. The median decrease in flow volume was 12 ml, with a median relative decrease of 8%. However, there was no consistent reduction in aneurysm size; most aneurysms demonstrated a median increase in volume for 46 ml and median increase in diameter for 18 mm.

CONCLUSIONS

While MFMs offer a potential alternative for high-risk aortic aneurysm patients, their effectiveness in preventing aneurysm expansion is limited. The results suggest that MFMs can provide a stable hemodynamic environment but do not reliably reduce aneurysm size. This underscores the need for ongoing vigilance and long-term monitoring in patients treated with this technology.

Multilayer Flow Modulator Stent for Aortic Pathology: A Meta-Analysis and Additional Data from a Single-Centre Retrospective Cohort

Background

Thoracoabdominal aneurysms and aortic dissections are a challenge for vascular surgeons. Open surgery, fenestrated or branched endograft, and the chimney technique are not possible in some patients, because of comorbidities or anatomical restrictions. However, the multilayer flow modulator (MFM) can be implanted in some of these patients. In this systematic review, we will describe the experience with the multilayer stent. To augment the limited number of studies available, we will include a cohort of patients from our hospital.

Methods

We retrieved data on all consecutive patients treated using the MFM between May 2013 and August 2020. This included patients with type B dissections and thoracoabdominal or thoracic aneurysms who were unfit for open surgery. The systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We included all the studies that used the MFM in the aortic segment. Single-arm meta-analyses were performed using OpenMeta (Brown University, Providence, RI, USA).

Results

A total of 37 patients were treated in our hospital during the study period. The technical success was 97.3% and the 30-day mortality was 5.4%. In 40.5% of the included patients, the instructions for use were not followed. Off-label implantation was associated with a higher aneurysm-related mortality. A total of 12 studies were included in the meta-analysis and the technical success was 97.8%. In 68.5%, the aneurysm sack or false lumen remained perfused, 97% of all the covered side branches remained patent. After a follow-up period of 1 year, five patients in the meta-analysis presented with a ruptured aneurysm.

Conclusions

The overall quality of evidence is poor because long-term results are lacking, patients are frequently lost during follow-up and all the studies were non-comparative. Our retrospective study suggests a relatively low incidence of perioperative complications, although there was a high incidence of persistent perfusion in the aneurysm sac (102 of 149 patients). The risk of rupture at the 1-year follow-up was 2.1%.

Endovascular treatment of complicated aortic aneurysms using a modified flow-diverting strategy: Mid- to long-term outcome from a multicenter cohort study

OBJECTIVES

Frequently reported adverse events following flow-diverting stents' treatment of aortic aneurysms indicate further refinements of this technique are required. This study aims at evaluating the clinical efficacy of an improved flow-diverting strategy.

METHODS

A modified flow-diverting procedure was utilized in selected patients, in which stent-grafts were used to cover the non-branched segment of the aneurysmal lesion while flow-diverting multilayered bare metal stents were applied to cover the reno-visceral segment. The safety and efficacy of this joint procedure were assessed by regular follow-up.

RESULTS

We screened 497 patients and included 67 cases (mean age: 67.07 ± 12.14 years; 53 males) between February 2012 and March 2018. The median number of stent-grafts and bare metal stents used in the procedure were 1 (range: 1 to 3) and 3 (range: 2 to 4), respectively. During a mean follow-up period of 34.54 ± 20.28 months, aneurysm maximum diameter decreased from 64.79 ± 10.31 to 59.32 ± 10.20 mm (p = 0.002), while sac thrombosis ratio increased from 26.01±10.99% to 98.46±4.84% (p<0.001). Aneurysm-related death or conversion to open repair was documented in three patients. The majority side-branches (198/201) remained patent during follow-up. Overall clinical success rate reached 91.04% (61/67).

CONCLUSIONS

The joint procedure is characterized by significant aneurysm thrombosis along with high aneurysm stabilization/shrinkage and side-branches' patency rate. It might represent a potential improvement of the flow-diverting strategy in treating complex aortic lesions, yet large-scale, prospective, and randomized trials are anticipated to draw a robust conclusion.

ADVANCES IN KNOWLEDGE

The joint procedure could potentially exclude complex aortic aneurysms from circulation while maintaining the collateral branches.

Numerical Simulation of Blood Flows in Patient-specific Abdominal Aorta with Primary Organs

The abdominal aorta is the largest artery in the abdominal cavity that supplies blood flows to vital organs through the complex visceral arterial branches, including the celiac trunk (the liver, stomach, spleen, etc.), the renal arteries (the kidneys) and the superior and inferior mesenteric arteries (the small and large intestine, pancreas, etc.). An accurate simulation of blood flows in this network of arteries is important for the understanding of the hemodynamics in various organs of healthy and diseased patients, but the computational cost is very high. As a result, most researchers choose to focus on a portion of the artery or use a low-dimensional approximation of the artery. In the present work, we introduce a parallel algorithm for the modeling of pulsatile flows in the abdominal aorta with branches to the primary organs, and an organ-based two-level method for calculating the resistances for the outflow boundary conditions. With this highly parallel approach, the simulation of the blood flow for a cardiac cycle of the anatomically detailed aorta can be obtained within a few hours, and the blood distribution to organs including liver, spleen and kidneys are also computed with certain accuracy. Moreover, we discuss the significant hemodynamic differences resulted from the influence of the peripheral branches. In addition, we examine the accuracy of the results with respect to the mesh size and time-step size and show the high parallel scalability of the proposed algorithm with up to 3000 processor cores.

Stent graft coverage of dual-stent strategy in the management of abdominal aortic aneurysms

Treating an abdominal aortic aneurysm (AAA) with a stent graft (SG) and a multilayer stent (MS) is a key technology in isolating flow fields. Clinically, dual stents (an SG in the proximal and an MS in the distal of AAA) are used for treatment of AAA, but only a few studies have examined the relationship between SG coverage and treatment effects. Through numerical simulation of the hemodynamics after SG and MS implantation, the SG coverage and position were simulated at 0% (0 mm), 25% (13.75 mm), 50% (27.5 mm), and 75% (41.25 mm). With increasing SG coverage, the pressure on the aneurysm sac wall and the flow of branch vessels gradually decreased, and the lower wall shear stress (WSS) gradually increased. The changes in pressure, lower WSS, and the mass flow rate of the branch vessels did not change significantly. The coverage of the SG has a nonsignificant effect on hemodynamics in the treatment of AAA; the implantation position need not be very precise. This research can provide theoretic support for clinicians' decision-making.