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Editor's Choice – Mid Term Outcomes of Crossed Limb vs. Standard Limb Configuration in Endovascular Abdominal Aortic Aneurysm Repair: A Propensity Score Analysis

Open ArchivePublished:February 25, 2021DOI:https://doi.org/10.1016/j.ejvs.2021.01.018

      Objective

      The aim was to compare mid term outcomes between crossed limb (CL) and standard limb (SL) configuration in patients who underwent endovascular aortic aneurysm repair (EVAR).

      Methods

      This was a comparative cohort study. Eligible patients who underwent EVAR between September 2011 and March 2019 in a tertiary academic centre were included. Inverse probability of treatment weighting (IPTW) was used to balance the demographic, anatomical and operative baseline characteristics between the two groups. The primary outcome was adverse limb events including type IB endoleak (T1BEL), type III endoleak, and limb occlusion. Cox proportional hazards regression and marginal structural model were performed to compare time to event outcomes.

      Results

      The study included 729 patients (194 CL and 535 SL) with a median follow up of 34 months (interquartile range 16 – 62 months). The weighted analyses revealed no significant difference between CL and SL EVAR in terms of adverse limb events, type IA endoleak (T1AEL), type II endoleak (T2EL), re-intervention, and overall survival. In the subgroup analysis of large aneurysm sac, the CL configuration was associated with a significantly decreased risk of T1BEL (hazard ratio [HR] 0.31, 95% confidence interval [CI] 0.12 – 0.78, p = .014). Similar results were also observed in the subgroup of tortuous iliac arteries (HR 0.30, 95% CI 0.11 – 0.81, p = .017). After stratification by severe neck angulation, no significant difference was found between CL and SL EVAR for T1AEL, but the CL configuration was associated with a significantly increased risk of re-intervention (HR 2.69, 95% CI 1.31 – 5.51, p = .007). In addition, a trend towards a higher risk of adverse limb events in the CL group with severely angulated proximal neck was observed.

      Conclusion

      CL configuration in EVAR is safe and may be associated with a lower risk of T1BEL in patients with a large aneurysm sac or tortuous iliac arteries. However, it should be applied cautiously to aneurysms with a severely angulated neck due to the potentially higher risk of re-intervention.

      Keywords

      This cohort study with inverse probability of treatment weighting analyses suggests that endovascular aortic aneurysm repair (EVAR) with crossed limb (CL) configuration is safe and effective in general patients with abdominal aortic aneurysm and may decrease the risk of type IB endoleak in patients with a large aneurysm sac or tortuous iliac arteries. However, the application of the CL technique in patients with a severely angulated neck may be associated with a higher risk of re-intervention due to potential higher risks of adverse limb events.

      Introduction

      Endovascular aortic aneurysm repair (EVAR) has become the mainstream therapy for abdominal aortic aneurysm in patients with favourable anatomy. Hostile anatomical features, such as severely angulated neck or tortuous iliac arteries, can not only pose a challenge to cannulation of the contralateral gate of endograft but also increase the risk of aneurysm related complications.
      • Mathlouthi A.
      • Locham S.
      • Dakour-Aridi H.
      • Black J.H.
      • Malas M.B.
      Impact of suprarenal neck angulation on endovascular aneurysm repair outcomes.
      • Oliveira N.F.G.
      • Goncalves F.B.
      • Hoeks S.E.
      • Josee van Rijn M.
      • Ultee K.
      • Pinto J.P.
      • et al.
      Long-term outcomes of standard endovascular aneurysm repair in patients with severe neck angulation.
      • Coulston J.
      • Baigent A.
      • Selvachandran H.
      • Jones S.
      • Torella F.
      • Fisher R.
      The impact of endovascular aneurysm repair on aortoiliac tortuosity and its use as a predictor of iliac limb complications.
      Considering this problem, Ramaiah et al. described a crossed limb (CL) technique, also called the “ballerina” technique, which can facilitate gate cannulation and reduce the effect of neck angulation or iliac tortuosity on limb configuration.
      • Ramaiah V.G.
      • Thompson C.S.
      • Shafique S.
      • Rodriguez J.A.
      • Ravi R.
      • DiMugno L.
      • et al.
      Crossing the limbs: a useful adjunct for successful deployment of the AneuRx stent-graft.
      As the CL technique creates a non-standard limb configuration, several clinical studies have attempted to investigate its safety and effectiveness in recent years. In an anatomy matched cohort, no difference was found between the CL and standard limb (SL) configurations regarding short and mid term clinical outcomes.
      • Georgiadis G.S.
      • Georgakarakos E.I.
      • Antoniou G.A.
      • Trellopoulos G.
      • Argyriou C.
      • Nikolopoulos E.S.
      • et al.
      Clinical outcomes after crossed-limb vs. conventional endograft configuration in endovascular AAA repair.
      Similar results were also observed in a study focusing on patients with severely tortuous iliac arteries.
      • Yagihashi K.
      • Nishimaki H.
      • Ogawa Y.
      • Chiba K.
      • Murakami K.
      • Ro D.
      • et al.
      Early and mid-term results of endovascular aortic repair using a crossed-limb technique for patients with severely splayed iliac angulation.
      However, both studies were subject to limited sample size, with a maximum of 27 CL patients. Results of the current largest cohort, involving 43 CL and 269 SL patients, indicated comparable outcomes except for a greater risk of type II endoleak (T2EL) in the CL group.
      • Dattani N.
      • Wild J.
      • Sidloff D.
      • Fishwick G.
      • Bown M.
      • Choke E.
      • et al.
      Outcomes following limb crossing in endovascular aneurysm repairs.
      However, anatomical confounding factors were not addressed in this study, which might generate selection bias to the results. Although no studies compared the cannulation time between the two configurations quantitatively, the morphological advantage and technical convenience of the CL technique led to its widespread application but lacks well established clinical evidence in its safety and effectiveness.
      This study aimed to compare the mid term clinical outcomes of the CL and SL technique in a high volume single centre, with special focus on adjusted outcomes adverse iliac limb events involving type IB endoleak (T1BEL), type III endoleak (T3EL), and limb occlusion.

      Materials and methods

      Study design and approvals

      This observational cohort study compared outcomes of CL and SL configuration in patients who received EVAR and was reported in accordance with Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement of cohort studies (Supplementary Table S1), and approved by the institutional review board of West China Hospital. Patient informed consent was waived due to pre-existing and de-identified data in the retrospective study.

      Study cohort

      All consecutive patients with abdominal aortic aneurysm (AAA) treated by EVAR from September 2011 to March 2019 were reviewed in West China Hospital, which is a tertiary academic hospital in Chengdu, Sichuan, with a high volume of aortic procedures. The International Classification of Diseases 10th edition codes of the study population were I71.3 and I71.4. The exclusion criteria included: procedures not requiring implantation of iliac limb grafts, re-intervention of previous EVAR, and inadequate angiographic data.
      The included population was divided into CL and SL groups by two vascular surgeons according to the final angiogram. The CL or SL configuration was defined as the crossed or uncrossed bilateral iliac limb grafts in the anteroposterior view of final angiogram, respectively.
      • Ramaiah V.G.
      • Thompson C.S.
      • Shafique S.
      • Rodriguez J.A.
      • Ravi R.
      • DiMugno L.
      • et al.
      Crossing the limbs: a useful adjunct for successful deployment of the AneuRx stent-graft.
      All treatment strategies and peri-operative care were performed under a standard and unified protocol. All the patients in the study were implanted with the Endurant II or IIs Stent Graft (Medtronic, Minneapolis, MN, USA).

      Follow up and outcomes

      The patients who underwent EVAR were followed up in outpatient clinics by ultrasound imaging at one month, three months, 12 months, and annually thereafter. Computed tomography angiography (CTA) was adopted if adverse aneurysm specific complications, including type I or III endoleaks, limb occlusion, or increased diameter of the aneurysm sac, were observed. In addition, follow up via phone call was used to check the status of the patients if they could not come to outpatient clinics. The primary outcomes of interest were adverse limb events involving T1BEL, type III endoleak and limb occlusion. Secondary outcomes included re-intervention, type IA endoleak (TIAEL), T2EL, and overall survival.

      Covariates

      Demographic characteristics, smoking status, comorbidities, and anatomical variables were recorded by two investigators to address the potential confounding effect of covariates. The severity of comorbidities was evaluated by the Charlson Comorbidity Index. Anatomical variables were as follows: length of aneurysm neck, proximal neck oversizing ratio (OSR), neck angulation, maximum diameter of aneurysm sac, intramural thrombus load of aneurysmal sac, iliac tortuosity, common iliac artery aneurysm, distal iliac calcification, and distal limb OSR. All the diameters were measured from the minor axis of axial cuts or from planes perpendicular to the centreline in reformatted slices. The oversizing ratio was calculated as follows: (diameter of implanted stent graft – diameter of native artery in anchoring or landing zone)/diameter of native artery. Distal iliac calcification was defined as the circumferential proportion of calcified vessel wall at the iliac landing zone, which was estimated from the cross sectional images of the iliac arteries. The definition of severe neck angulation was similar to the previous study.
      • Oliveira N.F.
      • Bastos Goncalves F.M.
      • de Vries J.P.
      • Ultee K.H.
      • Werson D.A.
      • Hoeks S.E.
      • et al.
      Mid-Term results of EVAR in severe proximal aneurysm neck angulation.
      A large aneurysm sac was defined as a maximum diameter of the sac of > 70 mm. Intramural thrombus (IMT) load in the aneurysm sac was estimated as the area proportion of thrombus in the plane of maximum diameter, and heavy IMT was defined as a thrombus load over 50%. Iliac tortuosity was assessed by the pelvic artery index (PAI), counted as the arc length between aortic bifurcation and origin of common femoral artery divided by the shortest distance between the two landmarks.
      • Taudorf M.
      • Jensen L.P.
      • Vogt K.C.
      • Gronvall J.
      • Schroeder T.V.
      • Lonn L.
      Endograft limb occlusion in EVAR: iliac tortuosity quantified by three different indices on the basis of preoperative CTA.
      Common iliac artery aneurysm was defined as any aneurysmal dilation of the common iliac arteries with a diameter > 24 mm. A tortuous iliac artery was defined as a PAI of > 1.6.

      Statistical analysis

      Continuous variables with normal distribution were described as mean ± standard deviation (SD) and variables with non-symmetric distribution as median (interquartile ranges). Continuous variables were compared between the two groups with the Student t test or Mann–Whitney U test. Categorical variables were compared using Fisher’s exact test or the chi squared test. Cox proportional hazard regression analysis and marginal structural model were adopted to assess the association between limb configuration and time to event outcomes.
      • Robins J.M.
      • Hernan M.A.
      • Brumback B.
      Marginal structural models and causal inference in epidemiology.
      In order to account for baseline differences between the two groups, inverse probability of treatment weighting (IPTW) adjusted analyses was performed.
      • Austin P.C.
      • Stuart E.A.
      Moving towards best practice when using inverse probability of treatment weighting (IPTW) using the propensity score to estimate causal treatment effects in observational studies.
      The propensity to undergo CL EVAR vs. SL EVAR was estimated by a logistic regression model based on age, gender, Charlson Comorbidity Index, anaesthesia, aneurysm rupture, coexisting common iliac artery aneurysms, length of aneurysmal neck, proximal neck oversizing ratio, neck angulation, maximum diameter of aneurysm sac, intramural thrombus load of aneurysmal sac, iliac tortuosity, distal iliac calcification, and distal limb oversizing ratio. The weighted balance between groups was assessed by standardised differences, and an excellent balance was considered when the standardised differences were < 0.10.
      • Austin P.C.
      • Stuart E.A.
      Moving towards best practice when using inverse probability of treatment weighting (IPTW) using the propensity score to estimate causal treatment effects in observational studies.
      Sensitivity analysis was conducted to stabilise the weights by truncating the non-overlapping tails of the propensity score distributions which were below and above the 1st and 99th percentiles.
      • Austin P.C.
      • Stuart E.A.
      Moving towards best practice when using inverse probability of treatment weighting (IPTW) using the propensity score to estimate causal treatment effects in observational studies.
      Subgroup analysis was conducted in terms of severe neck angulation, large aneurysm sac, heavy IMT, and tortuous iliac artery. Multiple imputation was adopted to account for missing data. All statistical analyses were performed using R studio Version 1.2.1335 (http://www.R-project.org) and Empower(R) (www.empowerstats.com, X&Y solutions, Inc., Boston, MA).

      Results

      Baseline characteristics

      A total of 821 patients were screened according to the selection criteria and finally 729 patients were included. The detailed flow diagram is shown in Figure 1. Among the 729 patients eligible for analysis, 194 adopted the CL configuration and 535 the SL technique. Baseline characteristics of the unweighted and weighted cohorts are shown in Table 1, Table 2, respectively. The demographics of two the groups were comparable in age and comorbidities. However, the anatomical parameters of patients in the CL group were more complex than those in the SL group, with more severely angulated aneurysm neck (44.33% vs. 22.43%), larger aneurysm diameter (59.19 ± 14.47 vs. 53.14 ± 13.86 mm) and higher pelvic artery index (1.37 ± 0.25 vs. 1.28 ± 0.17). After IPTW adjustment, an excellent balance was achieved for all propensity score variables, and the weighted cohort displayed well matched baseline characteristics regarding age, gender, comorbidities, operative, and anatomical parameters (Table 2). The standardised differences of variables used to generate the propensity score before and after weighting are shown in Supplementary Figure S1.
      Figure 1
      Figure 1Strengthening the reporting of observational studies in epidemiology (STROBE) flow diagram of selection of patients undergoing endovascular abdominal aortic aneurysm repair (EVAR).
      Table 1Baseline characteristics of the unweighted study cohort of 729 patients treated by endovascular aortic aneurysm repair with standard limb or crossed limb configuration
      VariablesStandard limb (n = 535)Crossed limb (n = 194)p
      p value of difference in baseline characteristics between two groups.
      Standardised difference (95% CI)
      Standardised difference showing unweighted balance before inverse probability treatment weighting.
      Continuous
       Age – y71.49 ± 8.2772.51 ± 8.56.150.12 (–0.04 – 0.29)
       Charlson score1 (1–2)1 (1–2).510.06 (–0.11 – 0.22)
       Neck diameter – mm21.35 ± 2.7421.57 ± 2.80.350.08 (–0.09 – 0.24)
       Neck length – mm29.15 ± 13.4326.60 ± 12.34.0210.20 (0.03 – 0.36)
       Neck OSR0.21 ± 0.060.21 ± 0.06.830.02 (–0.15 – 0.18)
       Max. aneurysm diameter – mm53.14 ± 13.8659.19 ± 14.47<.0010.43 (0.26 – 0.59)
       IMT load0.20 (0.10–0.50)0.30 (0.10–0.50).400.07 (–0.09 – 0.23)
       Min. limb OSR0.06 (0.00–0.09)0.06 (0.00–0.10).270.09 (–0.07 – 0.26)
       Max. limb OSR0.11 (0.08–0.15)0.12 (0.08–0.15).600.04 (–0.12 – 0.21)
       Max. PAI1.23 (1.15–1.38)1.30 (1.19–1.48)<.0010.41 (0.24 – 0.58)
       Max. calcification0.20 (0.10–0.40)0.20 (0.10–0.40).850.02 (–0.15 – 0.18)
      Categorical
       Female sex74 (13.83)49 (25.26)<.0010.29 (0.13 – 0.46)
       Smoking history331 (61.99)109 (56.48).180.11 (–0.05 – 0.28)
       Hypertension342 (63.93)129 (66.49).520.05 (–0.11 – 0.22)
       Diabetes66 (12.34)19 (9.79).350.08 (–0.08 – 0.25)
       COPD84 (15.73)30 (15.46).930.01 (–0.16 – 0.17)
       Stroke21 (3.93)7 (3.61).840.02 (–0.15 – 0.18)
       Coronary intervention63 (11.78)22 (11.34).870.01 (–0.15 – 0.18)
       Dysrhythmia18 (3.36)3 (1.55).200.12 (–0.05 – 0.28)
       CKD 4-523 (4.30)3 (1.55).0770.16 (–0.00 – 0.33)
       PAD26 (4.86)9 (4.64).900.01 (–0.15 – 0.17)
       General anaesthesia136 (25.42)65 (33.51).0310.18 (0.01 – 0.34)
       Rupture39 (7.29)24 (12.37).0310.17 (0.01 – 0.34)
       CIAA143 (26.73)57 (29.38).480.06 (–0.11 – 0.22)
       IIAA78 (14.58)31 (15.98).640.04 (–0.13 – 0.20)
       Limb extension to EIA156 (29.16)47 (24.23).190.11 (–0.05 – 0.28)
       Severe neck angulation120 (22.43)86 (44.33)<.0010.48 (0.31 – 0.64)
       Tortuous iliac arteries27 (5.09)29 (15.18)<.0010.34 (0.17 – 0.51)
       Large aneurysm sac65 (12.15)46 (23.71)<.0010.30 (0.14 – 0.47)
       Heavy IMT load163 (30.47)66 (34.02).360.08 (–0.09 – 0.24)
       Outside IFU usage129 (24.11)86 (44.33)<.0010.44 (0.27 – 0.60)
      Data are presented as n (%), mean ± standard deviation or median (interquartile range). CI = confidence interval; OSR = oversizing ratio; IMT = intramural thrombus; Min. = minimum value; Max. = maximum value; PAI = pelvic artery index; COPD = chronic obstructive pulmonary disease; CKD = chronic kidney disease; PAD = peripheral artery disease; CIAA = common iliac artery aneurysm; IIAA = internal iliac artery aneurysm; EIA = external iliac artery; IFU = instruction for use.
      p value of difference in baseline characteristics between two groups.
      Standardised difference showing unweighted balance before inverse probability treatment weighting.
      Table 2Baseline characteristics of the weighted study cohort of 729 patients treated by endovascular aortic aneurysm repair with standard limb or crossed limb configuration
      VariablesStandard limb (n = 535)Crossed–limb (n = 194)p
      p value of difference in baseline characteristics between the groups.
      Standardised difference (95% CI)
      Standardised difference showing weighted balance after inverse probability treatment weighting, and excellent balance was considered when standardised differences <0.10.
      Continuous
       Age – y71.84 ± 8.1472.34 ± 9.23.440.058 (–0.045 – 0.160)
       Charlson score1 (1–2)1 (1–2).570.042 (–0.060 – 0.145)
       Neck diameter – mm21.39 ± 2.7821.45 ± 2.65.760.023 (–0.080 – 0.125)
       Neck length – mm28.49 ± 13.1028.41 ± 12.83.930.006 (–0.096 – 0.109)
       Neck OSR0.21 ± 0.060.21 ± 0.06.870.012 (–0.091 – 0.115)
       Max. aneurysm diameter – mm54.87 ± 15.2655.42 ± 14.01.610.038 (–0.065 – 0.141)
       IMT load0.28 (0.09–0.50)0.29 (0.11–0.50).960.004 (–0.099 – 0.106)
       Min. limb OSR0.06 (0.00–0.10)0.06 (0.00–0.11).960.004 (–0.099 – 0.106)
       Max. limb OSR0.11 (0.07–0.15)0.12 (0.08–0.16).410.061 (–0.042 – 0.163)
       Max. PAI1.29 (1.12–1.46)1.29 (1.11–1.48).850.014 (–0.089 – 0.116)
       Max. calcification0.20 (0.10–0.40)0.20 (0.10–0.40).590.040 (–0.063 – 0.142)
      Categorical
       Female sex16.9917.54.840.015 (–0.088 – 0.117)
       Smoking history60.1257.76.520.048 (–0.055 – 0.150)
       Hypertension65.0968.72.300.077 (–0.025 – 0.180)
       Diabetes11.9411.67.910.008 (–0.094 – 0.111)
       COPD16.0912.57.180.098 (–0.002 – 0.203)
       Stroke4.043.3.590.040 (–0.063 – 0.142)
       Coronary intervention11.9212.3.880.012 (–0.091 – 0.114)
       Dysrhythmia4.072.88.380.065 (–0.037 – 0.168)
       CKD 4-53.633.14.720.027 (–0.076 – 0.130)
       PAD4.734.79.970.003 (–0.100 – 0.105)
       General anaesthesia27.1526.68.890.011 (–0.092 – 0.113)
       Rupture8.769.56.710.028 (–0.075 – 0.130)
       CIAA34.8236.15.710.028 (–0.075 – 0.130)
       IIAA15.0516.46.600.039 (–0.064 – 0.141)
       Limb extension to EIA27.9928.6.860.014 (–0.089 – 0.116)
       Severe neck angulation28.1627.56.860.014 (–0.089 – 0.116)
       Tortuous iliac arteries6.587.76.540.046 (–0.057 – 0.148)
       Large aneurysm sac15.417.71.400.062 (–0.040 – 0.165)
       Heavy IMT load31.1729.93.720.027 (–0.076 – 0.130)
       Outside IFU usage30.1127.62.460.055 (–0.048 – 0.157)
      Data are presented as % or mean ± standard deviation or median (interquartile range). OSR = oversizing ratio; IMT = intramural thrombus; Min. = minimum value; Max. = maximum value; PAI = pelvic artery index; COPD = chronic obstructive pulmonary disease; CKD = chronic kidney disease; PAD = peripheral artery disease; CIAA = common iliac artery aneurysm; IIAA = internal iliac artery aneurysm; EIA = external iliac artery; IFU = instruction for use.
      p value of difference in baseline characteristics between the groups.
      Standardised difference showing weighted balance after inverse probability treatment weighting, and excellent balance was considered when standardised differences <0.10.

      Adverse limb events

      The median ultrasound or CTA follow up after EVAR was 13 months (interquartile range 4 – 34 months), 40 (5.49%) patients were lost to follow up and did not receive any ultrasound or CTA examination. No significant difference was found regarding the loss to follow up between groups (5.67% vs. 5.42%, p = .87). A total of 61 patients suffered from adverse limb events during follow up, with 21 (11.48%) in the CL group and 40 (7.91%) in the SL group. The adverse limb events included 11 (6.01%) T1BELs, 4 (2.20%) type III endoleaks, and 7 (3.83%) limb occlusions in the CL group; and 23 (4.55%) T1BELs, 5 (0.99%) type III endoleaks, and 15 (2.95%) limb occlusions in the SL group. The 12 and 36 month rates of adverse limb events are shown in Table 2. In the unweighted analysis, no significant difference between the groups regarding adverse limb events (hazard ratio [HR] 1.20, 95% confidence interval [CI] 0.71 – 2.04, p = .495, Fig. 2), T1BEL (HR 1.02, 95% CI 0.50 – 2.11, p = .95) and limb occlusion (HR 1.13, 95% CI 0.46 – 2.78, p = .79). In the IPTW weighted cohort, CL technique was associated with a significantly decreased risk of T1BEL (HR 0.56, 95% CI 0.34 – 0.92, p = .023). However, sensitivity analysis after truncation of non-overlapping propensity scores suggested no significant difference in T1BEL between the groups (Table 3).
      Figure 2
      Figure 2Cumulative Kaplan–Meier estimates of freedom from adverse limb events in whole cohort in (A) unadjusted analysis and (B) inverse probability of treatment weighting analysis in patients treated with endovascular aneurysm repair (EVAR) with crossed limb (CL) or standard limb (SL) configuration.
      Table 3Comparison of mid term outcomes between crossed and standard limb configuration in overall cohort and subgroups of patients treated by endovascular aortic aneurysm repair in unadjusted and inverse probability of treatment weighted (IPTW) analyses
      SubgroupsPatients – nUnadjusted analysis HR (95% CI)IPTW analysis HR (95% CI)IPTW sensitivity analysis HR (95% CI)
      Overall cohort
       Adverse limb events6881.20 (0.71–2.04)0.88 (0.62–1.25)1.32 (0.87–2.00)
       T1BEL6881.02 (0.50–2.11)0.56 (0.34–0.92)1.07 (0.65–1.77)
       T3EL6882.04 (0.55–7.60)2.36 (0.63–8.79)1.07 (0.29–3.95)
       Limb occlusion6881.13 (0.46–2.78)0.84 (0.46–1.53)1.03 (0.52–2.02)
       T1AEL6880.76 (0.27–2.12)0.50 (0.24–1.03)0.96 (0.47–1.98)
       T2EL6880.81 (0.54–1.22)0.83 (0.64–1.06)0.81 (0.60–1.10)
       Re-intervention7181.69 (0.90–3.16)1.05 (0.68–1.62)1.69 (0.99–2.67)
       Overall survival7181.22 (0.84–1.79)1.22 (0.96–1.56)1.26 (0.95–1.67)
      Severely angulated neck
       Adverse limb events1921.98 (0.83–4.75)1.55 (0.88–2.73)1.71 (0.93–3.24)
       T1BEL1921.60 (0.61–4.23)1.32 (0.68–2.57)1.33 (0.68–2.59)
       T3EL1920.61 (0.06–6.74)1.67 (0.41–6.88)NA
       Limb occlusion1922.31 (0.42–12.63)1.10 (0.38–3.21)1.12 (0.38–3.24)
       T1AEL1920.75 (0.21–2.67)0.83 (0.32–2.15)0.83 (0.32–2.15)
       T2EL1920.72 (0.40–1.32)0.78 (0.52–1.17)0.77 (0.50–1.18)
       Re-intervention2012.78 (1.04–7.41)
      Statistically significant.
      2.69 (1.31–5.51)
      Statistically significant.
      1.51 (1.14–4.07)
      Statistically significant.
       Overall survival2011.33 (0.70–2.53)1.34 (0.86–2.09)1.34 (0.86–2.09)
      Large aneurysm sac
       Adverse limb events1040.63 (0.17–1.61)0.41 (0.18–0.92)
      Statistically significant.
      0.771 (0.33–1.81)
       T1BEL1040.36 (0.10–1.39)0.31 (0.12–0.78)
      Statistically significant.
      0.34 (0.15–0.81)
      Statistically significant.
       T3EL104NANANA
       Limb occlusion1043.44 (0.35–33.59)0.92 (0.25–3.33)1.00 (0.27–3.66)
       T1AEL1040.44 (0.08–2.32)0.62 (0.20–1.98)0.73 (0.23–2.35)
       T2EL1040.55 (0.23–1.36)0.81 (0.48–1.35)0.65 (0.18–1.01)
       Re-intervention1101.00 (0.35–2.80)0.76 (0.37–1.58)1.15 (0.56–2.38)
       Overall survival1100.62 (0.27–1.44)0.53 (0.30–0.93)0.75 (0.43–1.32)
      Tortuous iliac arteries
       Adverse limb events540.91 (0.32–2.64)0.87 (0.42–1.78)1.06 (0.48–2.33)
       T1BEL540.37 (0.09–1.54)0.30 (0.11–0.81)
      Statistically significant.
      0.31 (0.10–0.95)
      Statistically significant.
       T3EL54NANANA
       Limb occlusion541.92 (0.37–10.08)1.63 (0.68–3.91)0.95 (0.34–2.64)
       T1AEL54NA1.13 (0.15–8.75)NA
       T2EL540.69 (0.17–2.84)0.31 (0.12–0.81)0.60 (0.22–1.65)
       Re-intervention543.13 (0.64–15.16)2.44 (0.83–7.19)1.97 (0.74–5.24)
       Overall survival541.86 (0.36–9.60)3.10 (0.83–11.57)1.51 (0.71–3.22)
      Heavy IMT load
       Adverse limb events2200.97 (0.42–2.24)0.54 (0.31–1.05)1.17 (0.62–2.21)
       T1BEL2200.90 (0.32–2.55)0.52 (0.26–1.06)0.82 (0.41–1.65)
       T3EL2201.87 (0.12–29.91)1.95 (0.24–16.09)4.64 (0.56–38.19)
       Limb occlusion2201.00 (0.26–3.90)0.44 (0.16–1.18)0.66 (0.25–1.78)
       T1AEL2202.00 (0.13–31.98)0.88 (0.09–8.87)1.38 (0.14–13.85)
       T2EL2200.24 (0.07–0.80)
      Statistically significant.
      0.31 (0.18–0.56)
      Statistically significant.
      0.14 (0.05–0.38)
      Statistically significant.
       Re-intervention2261.69 (0.45–6.32)1.39 (0.56–3.46)2.30 (0.93–5.71)
       Overall survival2261.41 (0.78–2.57)1.16 (0.78–1.74)1.54 (1.00–2.36)
      IPTW = inverse probability treatment weighting; T1BEL = type IB endoleak; T1AEL = type IA endoleak; T2EL = type II endoleak; T3EL = type III endoleak; IMT = intramural thrombus; NA = not available.
      Statistically significant.
      In the subgroup analysis of the large aneurysm sac, the CL configuration was associated with a significantly decreased risk of T1BEL (HR 0.31, 95% CI 0.12 – 0.78, p = .014, Fig. 3). This result was further confirmed by sensitivity analysis (HR 0.34, 95% CI 0.15 – 0.81, p = .021). The CL configuration was also associated with a significantly decreased risk of T1BEL in patients with tortuous iliac artery (HR 0.30, 95% CI 0.11 – 0.81, p = .017, Fig. 3). Sensitivity analysis showed similar results in terms of the effect of CL configuration in tortuous iliac arteries (Table 3). In the subgroup of severely angulated neck, a trend towards a higher risk of adverse limb events was observed in CL group both in unadjusted and IPTW analysis (Table 3). A significant difference between the two limb configurations in any subgroup analysis was not observed for limb occlusion.
      Figure 3
      Figure 3Cumulative Kaplan–Meier estimates of freedom from type IB endoleak (T1BEL) in (A, C) unadjusted analysis and in (B, D) inverse probability of treatment weighting analysis of patients treated with endovascular aneurysm repair (EVAR) with crossed limb (CL) or standard limb (SL) configuration in subgroups of (A, B) large aneurysm sac and (C, D) tortuous iliac arteries.

      Type IA endoleak

      The rates of TIAEL were 2.73% and 2.77% in the CL and SL groups during follow up, respectively, and the overall rate in the whole cohort was 2.76% (the detailed events are shown in Supplementary Table S3). In the unadjusted analysis, there was no significant association between limb configuration and TIAEL in the whole cohort (HR 0.76, 95% CI 0.27 – 2.12, p = .60), which was consistent with the results of IPTW analysis (HR 0.50, 95% CI 0.24 – 1.03, p = .060, Fig. S2) and sensitivity analysis (HR 0.96, 95% CI 0.47 – 1.98, p = .92). After stratification by severe angulated neck, no significant association was observed between limb configuration and TIAEL in either unadjusted or IPTW analysis (Table 3). No significant difference was found in the other subgroup analyses.

      Type II endoleak

      A total of 124 (18.00%) patients were found to have T2EL during follow up, with 31 (16.94%) in the CL group and 93 (18.38%) in the SL group. In the overall population, no significant difference between limb configuration and T2EL was found in either unadjusted analysis or IPTW analysis. In the subgroup of patients with heavy IMT, the CL configuration was associated with a significantly decreased risk of T2EL in unadjusted and IPTW analysis (HR 0.24, 95% CI 0.07 – 0.80, p = .020; HR 0.31, 95% CI 0.18 – 0.56, p = .001, respectively). The result of sensitivity analysis was also similar to that observed in the patients with heavy IMT (HR 0.14, 95% CI 0.05 – 0.38, p = .001). As for other subgroup analyses, no significant difference was detected between limb configuration and T2EL (Table 3).

      Survival and re-intervention

      The median follow up time for survival status was 34 months (interquartile 16 – 62 months) in the whole population. During follow up, 122 (16.99%) patients died. Among them, 15 (2.09%) were due to aneurysm related events. The overall survival rates of the CL and SL group was 78.95% and 84.47% (p = .082), respectively. In the unweighted cohort, no significant difference was found between limb configuration and overall survival in the whole cohort or subgroup population (Supplementary Fig. S3). The IPTW and related sensitivity analyses further confirmed the results of the unadjusted analysis (Table 3).
      As for re-intervention during follow up, 41 (5.71%) patients underwent re-intervention, including 16 (8.76%) in CL group and 25 (4.73%) in SL group. The detailed causes of re-intervention are summarised in Supplementary Table S4. Among the causes of re-intervention, endoleaks were the most common complications, involving 11 patients with T1BEL, six patients with T1AEL, five patients with both T1AEL and T1BEL, four patients with T2EL. In the overall population, no significant difference was found between limb configuration and re-intervention in unadjusted and IPTW analysis. After stratification by severely angulated neck, the CL configuration was associated with a significantly increased risk of re-intervention both in unadjusted and IPTW analysis (HR 2.78, 95% CI 1.04 – 7.41, p = .041; HR 2.69, 95% CI 1.31 – 5.51, p = .007, respectively, Fig. 4).
      Figure 4
      Figure 4Cumulative Kaplan–Meier estimate of freedom from re-intervention in the subgroup of patients treated by endovascular repair (EVAR) of aneurysms with severely angulated neck with crossed limb (CL) or standard limb (SL) configuration in (A) unadjusted analysis and in (B) inverse probability of treatment weighting analysis.

      Discussion

      Due to the relatively low quality of evidence in current studies, specific recommendations on how best to decide upon the configuration of stent graft limbs according to patient specific aortic anatomy during EVAR remains unavailable in recent guidelines.
      • Wanhainen A.
      • Verzini F.
      • Van Herzeele I.
      • Allaire E.
      • Bown M.
      • Cohnert T.
      • et al.
      Editor’s Choice – European Society for Vascular Surgery (ESVS) 2019 clinical practice guidelines on the management of abdominal aorto-iliac artery aneurysms.
      ,
      • Chaikof E.L.
      • Dalman R.L.
      • Eskandari M.K.
      • Jackson B.M.
      • Lee W.A.
      • Mansour M.A.
      • et al.
      The Society for Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm.
      In comparison with previous related evidence, this study represents a large comparative cohort study that fully accounts for the differences in the propensity to receive the CL or SL technique. After IPTW adjustment, the results suggest that the CL and SL configurations are comparable regarding midterm outcomes in the overall population, however, the CL configuration is associated with a significantly decreased risk of T1BEL in patients with large aneurysm sac or patients with tortuous iliac arteries. In addition, it should also be noted that CL technique is associated with an increased risk of re-intervention in patients with a severely angulated neck.
      In clinical practice, the CL configuration is adopted more frequently in patients with hostile anatomy, for instance severely angulated neck, large aneurysm sac and tortuous iliac arteries, etc. The underlying reason of crossing the limbs mainly involves reducing the acuity of the angle at the aortic neck and the iliac gate and facilitating the catheterisation of the short iliac gate. Thus, comparison of clinical outcomes concerning two limb configurations in real world data is challenging because of considerable selection bias and different treatment propensity. As noted in the baseline characteristics of the consecutive cohort in the study, the anatomical features of patients who underwent EVAR with the CL configuration were more complicated, with greater aneurysm neck angulation, larger aneurysm diameter and more tortuous iliac arteries. In order to address this problem, IPTW analysis was used to adjust the treatment propensity accounting for demographics, comorbidities, aortic anatomy, and stent graft oversizing ratios. The baseline characteristics of the weighted cohort were all comparable for the two limb configurations and the results of standardised difference also confirmed the well balanced propensity scores, which both indicated the robustness of the IPTW adjusted results.
      The findings of the study have several important implications for clinical practice. First, the CL configuration seemed to be more stable in aneurysms with a large sac or tortuous iliac arteries, as it was found to be associated with a decreased risk of T1BEL. From a biomechanical point of view, significant upward displacement force of the stent graft limb was considered to be correlated with T1BEL,
      • Molony D.S.
      • Kavanagh E.G.
      • Madhavan P.
      • Walsh M.T.
      • McGloughlin T.M.
      A computational study of the magnitude and direction of migration forces in patient-specific abdominal aortic aneurysm stent-grafts.
      and previous studies suggested an unignorable role of flow induced displacement forces in stent graft iliac limbs.
      • Roos H.
      • Tokarev M.
      • Chernoray V.
      • Ghaffari M.
      • Falkenberg M.
      • Jeppsson A.
      • et al.
      Displacement forces in stent grafts: influence of diameter variation and curvature asymmetry.
      Recent studies demonstrated that high tortuosity could result in increased displacement forces in the distal segments of the artery,
      • Belvroy V.M.
      • Romarowski R.M.
      • van Bakel T.M.J.
      • van Herwaarden J.A.
      • Bismuth J.
      • Auricchio F.
      • et al.
      Impact of aortic tortuosity on displacement forces in descending thoracic aortic aneurysms.
      and low pressure in aneurysm sac could magnify the displacement force of the stent graft, especially in a large diameter sac.
      • Volodos S.M.
      • Sayers R.D.
      • Gostelow J.P.
      • Bell P.
      Factors affecting the displacement force exerted on a stent graft after AAA repair—an in vitro study.
      Thus, both tortuous iliac arteries and large aneurysm sac could pose challenges to the stability of the standard SL configuration during follow up. The results of the study indicated that the CL configuration may provide better limb related outcomes in AAAs with tortuous iliac arteries and large aneurysm sac, probably attributed to reduction in drag force on crossed stent grafts in such circumstances.
      • Stefanov F.
      • McGloughlin T.
      • Morris L.
      A computational assessment of the hemodynamic effects of crossed and non-crossed bifurcated stent-graft devices for the treatment of abdominal aortic aneurysms.
      Additionally, the CL endografts are associated with extra spatial length in the sac, which may act as a potential “buffer” to compensate for aneurysm sac shrinkage. The association between limb configuration and sac shrinkage requires further investigation, especially in patients with large sac.
      The second clinical implication of the findings is related to the association between the CL configuration and the decreased risk of T2EL in patients with a heavy IMT load. Both unadjusted and IPTW analysis supported this result, which was also confirmed by the trimmed IPTW sensitivity analysis. In contrast to the findings, a previous cohort study found a higher incidence of T2EL in patients with the CL configuration;
      • Dattani N.
      • Wild J.
      • Sidloff D.
      • Fishwick G.
      • Bown M.
      • Choke E.
      • et al.
      Outcomes following limb crossing in endovascular aneurysm repairs.
      however, their results did not adjust for anatomical parameters that may have introduced selection bias. It is the authors’ view that persistent T2EL and related sac expansion were determined by the flow dynamics of the culprit vessels. The flow field of the aneurysm sac,
      • Katahashi K.
      • Sano M.
      • Takehara Y.
      • Inuzuka K.
      • Sugiyama M.
      • Alley M.T.
      • et al.
      Flow dynamics of type II endoleaks can determine sac expansion after endovascular aneurysm repair using four-dimensional flow-sensitive magnetic resonance imaging analysis.
      and heavy IMT load were found to be protective factors of T2EL. The difference in the T2EL risk between the two limb configurations in the study suggested that the configuration of stent grafts in sac with heavy IMT load may covertly influence the flow dynamics of T2EL. Studies on computational fluid dynamics are needed to build a theoretical bridge on these subtle correlations.
      Third, despite the advantages of better limb related outcomes in certain groups of patients, the CL configuration may suffer from an increased risk of re-intervention in patients with severe neck angulation. Though no significant association was found between CL and any types of specific complications, a trend towards higher risk of adverse limb events in the CL group was observed. In terms of this issue, biomechanical studies suggested severe neck angulation was associated with higher upward drag force in stent graft limbs, which make them susceptible to limb failure in the long term.
      • Molony D.S.
      • Kavanagh E.G.
      • Madhavan P.
      • Walsh M.T.
      • McGloughlin T.M.
      A computational study of the magnitude and direction of migration forces in patient-specific abdominal aortic aneurysm stent-grafts.
      ,
      • Figueroa C.A.
      • Taylor C.A.
      • Yeh V.
      • Chiou A.J.
      • Zarins C.K.
      Effect of curvature on displacement forces acting on aortic endografts: a 3-dimensional computational analysis.
      However, there is limited information regarding whether crossing the limbs will affect the drag force of the stent graft. Taking the outcomes of T1AEL together, the study indicates that the CL configuration in AAA with a severely angulated neck is safe and can facilitate contralateral gate cannulation, but probably at a cost of greater re-intervention risk due to adverse limb events.
      The study also has several limitations to be noted during results interpretation. First, despite careful adjustment of baseline characteristics with IPTW, the study might still be subject to potential unmeasured confounding factors, such as iliac limb fixation length. To address this problem, sensitivity analyses were also performed to obtain more stabilised results by repeating the IPTW analysis after truncation of the non-overlapping tails of propensity weights between the groups. The main results of the sensitivity analysis were similar to those of the IPTW analysis, which further validated the robustness of the results. Second, the study was a retrospective cohort study and innate misclassification or information bias could not be avoided. Fortunately, the proportions of missing values for covariates were relatively low, from 3.02% to 4.25%, and multiple imputation was used to estimate the values. Furthermore, the rate of patients who were lost during the follow up was relatively low and balanced across groups (5.67% vs. 5.42%). Third, the imaging follow up was partially skewed compared with 34 months of telephone follow up, as some patients failed to come back for further ultrasound examination after a median of 13 months. However, no significant difference was found either in the length of imaging or telephone follow up between the two types of limb configuration. Colleagues are working on the long term alterations of computational fluid dynamics regarding different limb configurations, and may hopefully shed more light on the long term stability of limb configuration in the future. Fourth, as the study only adopted one type of the stent graft (Endurant Medtronic), the application of the results to other devices should be interpreted with caution and investigated further.

      Conclusion

      EVAR with a CL configuration is commonly applied to AAA patients with hostile anatomy. After accounting for demographic, anatomical and operative confounders, the CL configuration is safe and effective regarding midterm outcomes in overall AAA patients. Moreover, the CL configuration may be associated with a lower risk of T1BEL in patients with a large aneurysm sac or tortuous iliac arteries. However, it should also be noted that application of the CL technique in patients with a severely angulated neck may facilitate gate cannulation during operation but at the cost of a higher risk of re-intervention, due to potential increased risks of adverse limb events.

      Funding

      This work was supported by the Applied Basic Research Program of Sichuan Province (CN) (grant number: 2019YJ0026 ) and Sichuan Province Science and Technology Support Program (CN) (grant number: 2018YYJC )

      Conflict of interest

      None.

      Author contributions

      Conception and design: J.Z. and D.Y.; Surgery: J.Z. and B.H.; Data collection and check: J.W., C.W., T.W., Y.Y., Y.M.; Statistical analysis: T.W., C.W., J.W., D.Y., J.Z.; Writing the manuscript: J.W., T.W., C.W., Y.Y., B.H.; Critical revision of the manuscript: J.Z., D.Y., Y.M.. All authors gave final approval of the submitted version.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:

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      Linked Article

      • The Crossed Legs, “Ballerina” (or “Johnnie Walker”) Configuration: A Solution or Bottle Neck in Endovascular Aneurysm Repair?
        European Journal of Vascular and Endovascular SurgeryVol. 61Issue 4
        • Preview
          In this issue of EJVES, Wang et al.1 describe their experience of endovascular aneurysm repair (EVAR) with the crossed limb configuration vs. the standard limb configuration. This report is of interest because the authors included a significant number of patients, with a weighted analysis, and also provide a sufficient length of follow up, extending >5 years in some patients. However, the report deals with a single device experience and therefore the findings need to be interpreted with caution.
        • Full-Text
        • PDF
        Open Archive
      • Re: “Midterm Outcomes of Crossed Limb vs. Standard Limb Configuration in Endovascular Abdominal Aortic Aneurysm Repair: A Propensity Score Analysis”
        European Journal of Vascular and Endovascular SurgeryVol. 62Issue 4
        • Preview
          We read with interest the article written by Dr Wang and colleagues on the midterm outcomes of crossed limb vs. standard limb configuration in endovascular abdominal aortic aneurysm repair.1 As the authors acknowledge, their study adopted only one device type, i.e., the Endurant endograft (Medtronic), and as a result the application of their findings to other devices should be interpreted with caution and investigated further. We would like to add at this point that we have already investigated the crossed limb configuration in a previously published study,2 on 313 patients with aorto-iliac or isolated iliac aneurysms treated with the Gore Excluder endograft (W.
        • Full-Text
        • PDF
        Open Archive

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