Displacement Forces in Iliac Landing Zones and Stent Graft Interconnections in Endovascular Aortic Repair: An Experimental Study

Geometric Analysis of the Gore Excluder Conformable Endoprosthesis in the Infrarenal Aortic Neck: One Year Results of the EXCeL Registry

OBJECTIVE

The Gore Excluder Conformable Endoprosthesis (CEXC) is designed to treat challenging infrarenal anatomy because of its active angulation control, repositionability, and enhanced conformability. This study evaluated 30 day and one year position and apposition of the CEXC in the infrarenal neck.

METHODS

Patients treated with the CEXC between 2018 and 2022 with an available 30 day computed tomography angiogram (CTA) were selected from four hospitals in a prospective registry. Endograft apposition (shortest apposition length [SAL]) and position (shortest fabric distance [SFD]) were assessed on the 30 day and one year CTAs. Maximum infrarenal aortic curvature was compared between the pre- and post-operative CTAs to evaluate conformability of the CEXC.

RESULTS

There were 87 patients with a 30 day CTA, and for 56 of these patients the one year CTA was available. Median (interquartile range [IQR]) pre-operative neck length was 22 mm (IQR 15, 32) and infrarenal angulation was 52° (IQR 31, 72). Median SAL was 21.2 mm (IQR 14.0, 29.3) at 30 days for all included patients. The SAL in 13 patients (15%) was < 10 mm at 30 days, and one patient had a SAL of 0 mm and a type Ia endoleak. There was no significant difference in SAL between patients within and outside instructions for use. The SAL significantly increased by 1.1 mm (IQR -2.3, 4.7; p = .042) at one year. The SAL decreased in seven patients (13%), increased in 13 patients (23%), and remained stable in 36 patients (64%). Median SFD was 2.0 mm (IQR 0.5, 3.6) at 30 days, which slightly increased by 0.3 mm (IQR -0.5, 1.8; p = .019) at one year. One patient showed migration (SFD increase ≥ 5 mm). Median endograft tilt was 15.8° (IQR 9.7, 21.4). Pre-operative maximum infrarenal curvature was 36 m-1 (IQR 26, 56) and did not significantly change thereafter.

CONCLUSION

In most patients, the CEXC was implanted close to the renal arteries, and sufficient (≥ 10 mm) post-operative apposition was achieved at 30 days, which slightly increased at one year. Post-operative endograft tilt was relatively low, and aortic geometry remained unchanged after implantation of the CEXC, probably due to its high conformability.

The effect of stent graft curvature on the hemodynamic displacement force after abdominal aortic aneurysm endovascular repair

Endovascular aortic aneurysm repair is a minimally invasive procedure with low mortality and morbidity. Clinical studies have revealed that a displacement force (DF) can cause stent graft (SG) migration in some circumstances requiring repeated intervention. This study aims to determine the relationship between the SG curvature and the calculated DF from four patient-specific computational fluid dynamics models. The SG's curvature was defined according to the centrelines of the implanted SG's branches. The centrelines were defined as either intersecting or separated lines. The centreline curvature (CLC) metrics were calculated based on the local curvature radii and the distances from the centrelines of idealized straight branches. The average CLC value and average variation were calculated to represent the entire graft's curvature. These CLC calculations were compared, and the method that gave the best correlation to the calculated DF was found. The optimal correlation is obtained from calculating the CLC average variation using separated centrelines and distance from straight lines, with an R2 = 0.89. Understanding the relationship between vascular morphology and DF can help identify at-risk patients before the procedure. In these cases, we can provide appropriate treatment and follow up with the patient to prevent future failure.

Fast and Accurate Computation of the Displacement Force of Stent Grafts after Endovascular Aneurysm Repair

Purpose: Currently, the displacement force of stent grafts is generally obtained using computational fluid dynamics (CFD), which requires professional CFD knowledge to perform the correct simulation. This study proposes a fast, simple, and clinician-friendly approach to calculating the patient-specific displacement force after endovascular aneurysm repair (EVAR). Methods: Twenty patient-specific post-EVAR computed tomography angiography images were used to reconstruct the patient-specific three-dimensional models, then the displacement forces were calculated using CFD and the proposed approaches, respectively, and their numerical differences were compared and analyzed. Results: Based on the derivation and simplification of the momentum theorem, the patient-specific displacement forces were obtained using the information of the patient-specific pressure, cross-sectional area, and angulation of the two stent graft ends, and the average relative error was no greater than 1.37% when compared to the displacement forces calculated by CFD. In addition, the linear regression analysis also showed good agreement between the displacement force values calculated by the new approach and CFD (R = 0.999). Conclusions: The proposed approach can quickly and accurately calculate the patient-specific displacement force on a stent graft and can therefore help clinicians quickly evaluate the post-EVAR displacement force.

Remodeling of Abdominal Aortic Angulation and Curvature After Endovascular Aneurysm Repair in Patients With vs Without Late Type Ia Endoleak or Endograft Migration

PURPOSE

To investigate aortic remodeling of the supra- and infrarenal aorta from preoperative to 1 month and midterm follow-up after endovascular aneurysm repair (EVAR) by analyzing changes in angulation and curvature in patients with vs without late type Ia endoleak or device migration.

MATERIALS AND METHODS

From a multicenter database, 35 patients (mean age 76±5 years; 31 men) were identified with late (>1 year) type Ia endoleak or endograft migration (≥10 mm) and defined as the complication group. The control group consisted of 53 patients (mean age 75±7 years; 48 men) with >1-year computed tomography angiography (CTA) follow-up and no evidence of endoleaks. Suprarenal and infrarenal angles were measured on centerline reconstructions of the preoperative, 1-month, and midterm CTA scans. The value and location relative to baseline of maximum suprarenal and infrarenal curvature were determined semiautomatically using dedicated software. Changes were determined at 1 month compared with the preoperative CTA and at midterm compared with 1 month.

RESULTS

Preoperative suprarenal angulation was significantly greater in the complication group compared to the controls (34°±18° vs 24°±17°, p=0.008). It decreased significantly at 1 month in the complication group (29°±16°, p=0.011) and at midterm follow-up in the controls (20°±19°, p<0.001). Preoperative infrarenal angulation was not significantly different (57°±15° vs 49°±24°, p=0.114). This measurement increased significantly through midterm follow-up in the complication group (63°±23°, p<0.001) but remained stable in the controls (46°±22°). Preoperative suprarenal curvature was not significantly different (38±22 m^-1 vs 29±25 m^-1, p=0.115). This variable increased significantly through midterm follow-up in the complication group (44±22 m^-1) but remained constant in the controls (28±22 m^-1). Preoperative infrarenal curvature was significantly greater in the complication group (77±29 m^-1 vs 65±28 m^-1, p=0.047) and decreased significantly in both groups during midterm follow-up (50±17 m^-1 vs 41±19 m^-1 p=0.033). The location of the maximum curvature with regard to baseline shifted significantly distally in the complication group (54±43 to 72±41 mm, p<0.001), while it remained stable in the controls (46±33 to 48±31 mm).

CONCLUSION

At midterm follow-up, significant differences in supra- and infrarenal angulation and curvature were observed between patients with vs without type Ia endoleak or migration. The location of the maximum curvature shifted distally in patients with complications. The aortic morphology is more stable during midterm follow-up in the patients without endoleaks.

A Comparative Study of the Efficacy by using Different Stent Grafts in Bell-Bottom Technique for the Treatment of Abdominal Aortic Aneurysm Concomitant with Iliac Artery Aneurysm

BACKGROUND

Bell-bottom technique (BBT) is one method to preserve the internal iliac artery during endovascular aneurysm repair (EVAR) for abdominal aortic aneurysm (AAA) that extends to iliac artery. The data on the efficacy of this technique are still limited. We sought to evaluate the midterm efficacy of BBT by using different stent grafts in the treatment of AAA combined with iliac artery aneurysm (IAA).

METHODS

From January 2011 to December 2016, AAA patients with IAA using BBT to preserve the internal iliac artery were retrospectively analyzed in our institution. Patients were followed up at 3, 6, and then every 12 months after surgery. The outcomes among 3 types of stent grafts (Zenith, Excluder, and Endurant) were compared. BBT-related end points including type Ib endoleak, IAA sac expansion, distal neck expansion, and rupture during follow-up were compared. Other events including perioperative death, any other types of endoleak, and corresponding management were also documented.

RESULTS

A total of 125 patients with 141 IAAs were identified. Ninety-eight patients (78.4%) with 113 lesions (80.4%) received a median follow-up time of 38 months. The incidence of type Ib endoleak was 22.9%, 8.3%, 11.9%, and 14.2% (P = 0.19) in Zenith, Excluder, Endurant group, and total patients, respectively. The incidence of IAA sac enlargement was 17.1%, 5.6%, 7.1%, and 9.7% (P = 0.20). The incidence of IAA rupture was 8.6%, 0.0%, 0.0%, and 2.7% (P = 0.03). The incidence of IAA neck enlargement was 34.3%, 13.9%, 16.7%, and 21.2% (P = 0.07). Totally, 14 cases (10.7%) received further treatment for BBT-related issues.

CONCLUSIONS

Although BBT remains a safe and effective treatment option to preserve internal iliac artery during standard EVAR with acceptable complication rates in Asians, different IAA rupture rates were found among 3 different stent grafts. Our data for the first time revealed that the type of stent grafts has influence on the final clinical outcome. Based on that, iliac extension should be selected appropriately while treating AAA-IAA.

Early and Late Endograft Limb Proximal Migration with Resulting Type 1b Endoleak following an EVAR for Ruptured AAA

Introduction. Seal zone failure after EVAR leads to type 1 endoleaks and increases the risk of delayed aortic rupture. Type 1b endoleaks, although rare, represent a true risk to the repair. Case Presentation. We report the case of a 65-year-old female who underwent emergent endovascular repair for a ruptured infrarenal abdominal aortic aneurysm and developed bilateral type 1b endoleaks following proximal migration of both endograft limbs. The right-side failure was diagnosed within 48 hours from the initial repair and the left side at the 1-year follow-up. Both sides were successfully treated with endovascular techniques. A review of the literature with an analysis of potential risk factors is also reported. Conclusion. For patients undergoing EVAR for ruptured AAA and with noncalcified iliac arteries, more aggressive oversizing of the iliac limbs is recommended to prevents distal seal zone failures.

Re-interventions after endovascular aortic repair for infrarenal abdominal aneurysms: a retrospective cohort study

Background

Early morbidity and mortality are generally lower after endovascular aortic repair (EVAR), than after open repair but re-interventions and late complications are more common. The aim of the present study was to make a detailed description of re-interventions after EVAR-including incidence, indications, procedures, and outcome-with special reference to non-access-related re-interventions.

Methods

This is a retrospective single-center cohort study of re-interventions after standard EVAR with special reference to non-access-related re-interventions. Consecutive patients (n = 405) treated with standard EVAR for non-ruptured (n = 337) or ruptured (n = 68) infrarenal aneurysms between 2005 and 2013 were analysed. Median follow-up was 29 months (range 0–108).

Results

Eighty-nine patients (22 %) underwent 113 re-interventions during follow-up. Twenty-seven patients (7 %) had 28 access related re-intervention, 65 patients (16 %) had 85 non-access related reinterventions. Non-access related re-interventions were more common in ruptured aneurysms than in unruptured aneurysms (22 vs. 15 %, p = 0.002). The most frequent indications were endoleak type I (n = 19), type II (n = 21), or type III (n = 5); stent graft migration (n = 9); and thrombosis (n = 14). The most frequent procedures were embolization of endoleak type II (n = 21), additional iliac stent graft (n = 19), proximal extension (n = 12), thrombolysis (n = 8), iliac limb bare-metal stenting (n = 6), and stent graft relining (n = 7). Endovascular technique was used in 83 % of re-interventions.

Thirty-day mortality after non-access-related re-interventions was 15 % when initiated from symptoms (rupture or infection) and 0 % when initiated from follow-up findings (p = 0.014). Cumulative survival five years after EVAR was 72 % in patients with a re-intervention and 59 % in patients without (p = 0.21).

Conclusions

Non-access-related re-intervention rates are still considerable after EVAR and more frequent after ruptured aneurysms. Endoleak embolization is the most frequent procedure, followed by additional iliac stent grafts. Outcomes after re-interventions are generally good, except when initiated by rupture or infection.

Studying the Interaction of Stent-Grafts and Treated Abdominal Aortic Aneurysms

Since the advent of endovascular repair of aortic aneurysms (EVAR), clinical focus has been on preventing loss of sealing at the level of the infrarenal neck, which leads to type I endoleak and repressurization of the aneurysm sac. Enhanced mechanisms for central fixation and seal have consequently lowered the incidence of migration and endoleaks. However, endograft limb thrombosis and its causal mechanisms have not been addressed adequately in the literature. This article reviews the pathophysiological mechanisms associated with limb thrombosis in order to facilitate better clinical judgment to prevent iliac adverse effects.