Abstract
Objective
Venous stents are a common treatment modality for obstructive venous disease. Venous stents differentiate themselves by either a woven or braided structure, open or closed cell arrangement or based on material composition (elgiloy vs nitinol). Changes in the morphology of venous stents over time may contribute to restenosis or thrombosis. Woven elgiloy stents are prone to proximal and distal edge deformation compared with dedicated venous stents, which offer increased radial force at stent edges. The objective of this study is to describe luminal morphological changes among various venous stents and between woven to nonwoven venous stent configuration, over time.
Methods
A retrospective review at a single institution between January 2014 and June 2021 identified patients treated with venous stents. Patients with iliac and/or femoral venous stents with intraoperative intravascular ultrasound and a postoperative computed tomography scan were included in the study. Cross-sectional diameters measurements were taken at proximal, middle, and distal portions of each stent from intravascular ultrasound examination at the time of initial stenting and compared with the cross-sectional diameter measurements taken from computed tomography imaging at follow-up. A paired t test was used to compare the luminal change with a D'Agostino-Pearson test used for normality.
Results
Fifty-four stents distributed among 38 patients were identified. The mean time to follow-up was 17.5 months. Stents were placed in the common iliac vein (n = 37, 68.5%), external iliac vein (n = 14, 25.9%), and common femoral vein (n = 3, 5.6%). Implanted stents included the Boston Scientific Wallstent (n = 23, 42.6%), Bard Venovo (n = 3, 5.6%), Boston Scientific Vici (n = 23, 42.6%), and Medtronic Abre (n = 5, 9.3%). The mean luminal loss was measured at 2.12 mm proximally (95% confidence interval [CI], 1.64-2.60; P<.001), 1.29 mm at the mid-stent (95% CI, 0.83-1.74, P<.001), and 1.56 mm distally (95% CI, 0.99-2.12; P<.001). There was no significant difference in luminal changes between woven and nonwoven stents at proximal (P = .374), middle (P = .179), and distal (P = .609) stent measurements.
Conclusions
This study reports morphological changes within venous stents and between woven and nonwoven venous stents. Our findings demonstrate that the edge-stent luminal decrease traditionally attributed to woven configurations also occurs with the newer nonwoven stents. Additional factors such as anatomical location, pelvic curvature, and other external forces may be accountable for this change rather than geometrical configuration of the stent.
Keywords: Venous stent, Iliofemoral vein, Stent deformation, Woven venous stent, Nonwoven venous stent
Article Highlights.
-
•
Type of Research: Single-center retrospective cohort study
-
•
Key Findings: Over time, both woven and nonwoven venous stents demonstrate a significant decrease in diameter size at the proximal, middle, and distal portions of the stent (P < .001). Further analysis shows that this decreased diameter is similar between woven and nonwoven stents (P > .05).
-
•
Take Home Message: Edge-stent luminal reduction traditionally associated with woven venous stents also occurs in nonwoven venous stents. A significant reduction in diameter at all portions of the stent is present over time (P < .001), which suggests that other external factors may account for this change rather than geometrical configuration of the stent alone.
Venous stents have become a safe and effective method in treating venous insufficiency and obstruction.1 Venous disease can be defined by two different processes, a primary process, such as nonthrombotic iliac vein lesions, or a secondary process, such as post-thrombotic syndrome (PTS). In the case of nonthrombotic iliac vein lesions, the most common presentation occurs as a May-Thurner lesion when the right common iliac artery compresses the left common iliac vein.2 This chronic compression can lead to venous fibrosis and intraluminal stenosis, which causes chronic obstruction, reflux, and potentially deep vein thrombosis (DVT). In the case of post-thrombotic obstruction, ≤50% of patients will develop PTS after a DVT, even with anticoagulation therapy.1 In most cases, the occluded vein will recanalize partially and develop new collaterals. However, because recanalization and collaterals may be insufficient for adequate outflow, chronic obstruction and reflux develop.3 Furthermore, owing to the increased elasticity of veins in comparison with arteries, venoplasty alone has been shown to be insufficient for treating PTS.1
The Society for Vascular Surgery Guidelines from the American Venous Forum in 2014 describe venous stenting as a Grade 1, Evidence C recommendation for proximal chronic total venous occlusion or severe stenosis at risk for venous ulceration.4 Milder cases of venous insufficiencies are still treated with mostly compression therapy, with refractory cases potentially being considered for venous stenting.5 Venous stenting is performed with evidence of >50% stenosis and has been shown to significantly increase the quality of life in patients suffering from PTS.6,7
Venous stents exist in several types of conformations, including a woven or braided structure, open or closed cell structure, or different materials, such as elgiloy metal or nitinol.8 Nitinol stents are created with a material more compliant than stainless steel or composite metals to better mimic venous compliance.9 Braided structures are designed to provide a greater radial force to prevent collapse; however, these stents are historically known for edge stenosis due to being weaker at the proximal and distal ends.9,10 Newer dedicated venous stents may benefit from higher radial forces at the distal edges to prevent edge-stent stenosis. This study seeks to further describe woven vs nonwoven venous stent morphology and luminal changes over time.
Methods
This study was conducted with institutional review board approval and Health Insurance Portability and Accountability Act compliance. Patients were identified via retrospective review of the patients receiving venous stents at MedStar Health over a time period of January 2014 to June 2021. Criteria for inclusion in the study were any number of unilateral iliofemoral venous stents, use of intraoperative intravascular ultrasound (IVUS) imaging, and a postoperative computed tomography venogram (CTV). Fifty-four venous stents distributed among 38 patients were identified and kept for further analysis.
The cohort consisted of 25 female and 13 male patients with a mean age of 59 years over a range of 23 to 89 years. Other patient comorbidities are described in Table I. Indications for treatment included May-Thurner syndrome (n = 32) and PTS (n = 6) (Table II). Other notable preoperative characteristics included provocation (n = 13), hypercoagulability (n = 15), prior DVT (n = 16), prior pulmonary embolism (n = 4), concurrent pulmonary embolism (n = 2), prior venous intervention (n = 7), and inferior vena cava filter (n = 4) (Table II). As a study of primary patency, this cohort did not include any secondary interventions.
Table I.
Summary of demographic characteristics
| Characteristics | Mean (range) or No. (%) |
|---|---|
| Age | 59 (23-89) |
| Female | 25 (65.8) |
| Male | 13 (34.2) |
| BMI | 30.8 (18.1-48.8) |
| CHF | 2 (5.3) |
| CAD | 2 (5.3) |
| CKD | 2 (5.3) |
| DM | 4 (10.6) |
| Malignancy | 6 (15.9) |
| Smoker | 7 (18.4) |
BMI, Body mass index; CAD, coronary artery disease; CHF, congestive heart failure; CKD, chronic kidney disease; DM, diabetes.
Table II.
Summary of preoperative characteristics
| Indication | No. (%) |
|---|---|
| May Thurner syndrome | 32 (84.2) |
| PTS | 6 (15.8) |
| Hypercoagulable | 15 (39.5) |
| Provocation | 13 (34.2) |
| Prior DVT | 16 (42.1) |
| Prior PE | 4 (10.5) |
| Concurrent PE | 2 (5.3) |
| Prior lysis | 10 (26.3) |
| Prior venous intervention | 7 (18.4) |
| IVC filter | 4 (10.5) |
DVT, Deep vein thrombosis; IVC, inferior vena cava; PE, pulmonary embolism; PTS, post-thrombotic syndrome.
Two cross-sectional diameter measurements were taken at proximal, middle, and distal portions of each stent from IVUS examination at the time of initial stenting. On follow-up CTV imaging, two cross-sectional diameter measurements were again taken at the proximal, middle, and distal aspects of each stent. Per the MedStar Health protocol for CTV acquisition, all images are interpreted with 1-mm axial, sagittal, and coronal slices with contrast bolus administration at 3 mm/second after a 2-minute delay. The average of these diameters was then compared between the imaging modalities. Measurements performed on both imaging modalities were taken as the diameter from the inner wall to inner wall within the stent (Fig).
Figure.
Example of stent measurements on intravascular ultrasound (IVUS) examination compared with computed tomography (CT) imaging.
Postoperative antiplatelet and anticoagulation regimens included antiplatelet monotherapy, dual antiplatelet therapy, single antiplatelet and anticoagulation therapy, and dual antiplatelet therapy and anticoagulation therapy (Table III).
Table III.
Summary of postoperative antiplatelet and/or anticoagulation regimen
| Regimen | No. (%) |
|---|---|
| Single antiplatelet | 4 (10.5) |
| Dual antiplatelet | 1 (2.6) |
| Anticoagulation only | 8 (21.1) |
| Anticoagulation and single antiplatelet | 24 (63.2) |
| Anticoagulation and dual antiplatelet | 1 (2.6) |
The paired t test was used to compare the overall change in stent size between intraoperative IVUS and postoperative CT sizing with a significance of <0.05. The D'Agostino-Pearson test was used to test normality. The Kruskal-Wallis test was used to compare subgroups with significance at a P value of <.05.
Results
Fifty-four venous stents were implanted and compared with describe stent deformation over time. The mean time to follow-up with CT imaging was 17.5 months (interquartile range [IQR], 5.3-21.9). Thirty-seven (68.5%) were implanted in the common iliac vein, 14 stents (25.9%) implanted in the external iliac vein, and 3 stents (5.6%) implanted in the common femoral vein. Of the patients with implanted stents, 25 patients had a single stent (65.8%), 10 patients had 2 stents (26.3%), and 3 patients had 3 stents (7.9%) placed. Venous stent types included Boston Scientific (Marlborough, MA) Wallstent (n = 23, 42.6%), Bard (Franklin Lakes, NJ) Venovo (n = 3, 5.6%), Boston Scientific Vici (n = 23, 42.6%), and Medtronic (Minneapolis, MN) Abre (n = 5, 9.3%).
When considering all stents placed, the average intraoperative diameters measured 13.2 mm (IQR, 12.0-15.0 mm) proximally, 12.6 mm (IQR, 11.4-14.0 mm) in the middle, and 12.4 mm (IQR, 11.0, 14.4 mm) distally. The average postoperative diameters measured 11.2 mm (IQR, 10.0-12.5 mm) proximally, 11.4 mm (IQR, 10.0-12.5 mm) in the middle, and 10.9 mm (IQR, 9.5-12.0 mm) distally (Table IV). Using a paired t test, the change in diameter size was found to be significant (P < .001) at the proximal, middle, and distal locations (Table V).
Table IV.
Summary of the mean and median stent diameters (mm) on intravascular ultrasound (IVUS) examination intraoperatively and computed tomography (CT) scan postoperatively
| Intraoperative |
Postoperative |
|||||
|---|---|---|---|---|---|---|
| IVUS (proximal diameter) | IVUS (mid diameter) | IVUS (distal diameter) | CT (proximal diameter) | CT (mid diameter) | CT (distal diameter) | |
| Median | 13.3 | 12.3 | 12.3 | 11.0 | 11.0 | 10.3 |
| First quartile | 12.0 | 11.4 | 11.0 | 10.0 | 10.0 | 9.5 |
| Mean | 13.2 | 12.6 | 12.4 | 11.2 | 11.4 | 10.9 |
| Third quartile | 15.0 | 14.0 | 14.4 | 12.5 | 12.5 | 12.0 |
Table V.
Paired t test to compare intraoperative intravascular ultrasound (IVUS) examination diameter with postoperative computed tomography (CT) diameter, D'Agostino-Pearson test used to test normality
| Mean of difference, mm (95% CI) | P value | |
|---|---|---|
| Proximal diameter | 2.12 (1.64, 2.60) | <.001 |
| Middle diameter | 1.29 (0.83, 1.74) | <.001 |
| Distal diameter | 1.56 (0.99, 2.12) | <.001 |
CI, Confidence interval.
Further analysis was completed using subgroups to compare the change in diameter size between Wallstent (n = 23), woven elgiloy stents, with all other venous stents (n = 31) and nonwoven nitinol stents. At all portions of the measured stent proximally, in the middle, and distally, there were no significant differences found (P > .05).
Discussion
In this study, venous stent morphological changes over time suggests an overall trend toward luminal loss. For all stents, there is significance to the decrease in stent diameter over time in all measured stent locations. However, in subset analyses comparing woven with nonwoven venous stents, no significant differences were found in the luminal loss at all measured locations. The decrease in stent diameters at the proximal and distal edges of the stent is consistent with well-known morphological changes of Wallstents.9,10 The luminal loss across all portions of the stent may further suggest other external factors.
Although this study cannot conclude luminal loss as a direct causation of stent compromise leading to need for reintervention, the change in diameter may suggest clinical implications. Luminal loss because of in-stent restenosis (ISR) or stent compression have been identified as factors responsible for stent malfunction that may eventually require intervention. ISR has been found in ≤70% of iliofemoral stents placed, and some studies have attempted to establish causality owing to these reasons.11 However, the presence of ISR or stent compression alone does not mean a patient will experience symptoms or have a negative impact on quality of life. Furthermore, current practices do not recommend prophylactic treatment of asymptomatic lesions.11, 12, 13 Whether a certain level of luminal loss leads to reintervention remains to be seen.
Venous stent failure can occur owing to several other mechanisms besides luminal loss, such as neointimal formation, poor inflow or outflow, anticoagulation failure, or external compression.13, 14, 15 The majority of these causes have a more intrinsic etiology that may be present, regardless of the type of venous stent deployed. Neointimal changes can be associated with scarring that leads to stent deformation but may also be a product of the body's response to the conformational changes of the stent itself. Furthermore, several studies have demonstrated comparability in quality of life and patency between woven and nonwoven venous stenting in mid- to long-term periods.16,17 These findings suggest that other external factors may contribute to stent deformation. One study of venous stenting across the hip joint and inguinal ligament demonstrates a biomechanical effect on stents during high hip flexion and hyperextension.18 This additionally emphasizes the importance of anatomical considerations when placing venous stents.
There were several limitations to this study. The comparison of diameters measured on IVUS described in relation to CT imaging is important to address. First, each modality does not provide a perfect axial cross-section, which leads to obliquities that cannot be corrected completely. To combat this variability, two diameter measurements were taken for each stent and all measurements were taken as the inner diameter of the stent regardless of imaging modality. However, this strategy is unlikely to have eliminated this variability.
Further, variability in measurements is likely to be found just when comparing two different types of imaging modalities. A systematic review compares the use of IVUS examination compared with CT imaging in a diagnostic and therapeutic setting. IVUS examination is highly sensitive and specific when used to guide venous interventions. CTV has a high sensitivity with the additional benefit of being noninvasive; however, it may underestimate the severity and/or presence of stenotic disease.19 Another study provides additional data reporting that the mean CTV caliber difference was 2.5% larger in the common iliac vein and 7.3% larger in the external iliac vein when compared with IVUS measurements.20 Extrapolating these findings does suggest that measurements taken from our dataset postoperatively may underestimate the level of stenosis present across all portions of the stent. Ideally, future studies will be able to directly compare between the same imaging modalities. However, this process may be difficult owing to the invasive nature of IVUS examination, given that such maneuvers are typically performed in follow-up when concern for stent failure is present.
Another limitation is the small sample size at 54 stents among the 38 patients. As venous stenting becomes a more common modality of treating the various venous disease states, larger studies over a longer follow-up period can be achieved. This will allow for a more robust understanding of the luminal changes and how that can influence decisions on sizing recommendations.
Our database was created to include any length of follow-up time. Thus, luminal loss was not measured at standard intervals across all stents. If future studies were to investigate stent diameter changes over set intervals in follow-up, perhaps a trend may be found on the mechanics and rates of diameter decrease. To our knowledge, no existing studies have yet explored these structural changes in incremented periods.
An additional limitation is that luminal diameter changes in overlap zones between stents were not addressed in this study. There is a theoretical concern that the last 10 to 15 mm of elgiloy stents tend to be the weakest owing to the woven design.9,10 The reinforcement of these edges with overlap would be considered as a different biomechanical property. Owing to the woven nature of the stent design, conformational changes within the stent can affect the entirety of the stent. We did not assess the correlation of stent deformation between overlapped and nonoverlapped segments in this study, but if compared, may yield interesting findings.
The findings of this study suggest conformational changes at venous stent edges are similar to those historically described in Wallstents. However, the additional finding of a significant decrease the middle of the stent may also suggest another process at play leading to luminal loss. This study confirms the importance and need for further studies to describe the long-term changes, as well as the need for follow-up and maintenance of venous stents.
Conclusions
Our study investigated morphological changes within venous stents and between woven and nonwoven venous stents. The edge stent stenosis traditionally found in the woven or braided configuration of venous stents can also be seen in newer nonwoven stents. This finding is in addition to stenosis in the middle of the stent. This finding suggests that other external factors may be present, such as anatomical location or pelvic curvature, which may be causing all venous stents to develop luminal loss in a similar manner. To clearly identify such causes requires further investigation.
Author Contributions
Conception and design: JL, SA
Analysis and interpretation: JL, SA, JC, MK, SD
Data collection: JL, CC
Writing the article: JL, CC, JC, SD
Critical revision of the article: JL, SA, MK, SD
Final approval of the article: JL, SA, CC, JC, MK, SD
Statistical analysis: JL, CC, JC
Obtained funding: Not applicable
Overall responsibility: JL
SA and SD contributed equally to this article and share senior authorship.
Disclosures
None.
From the Eastern Vascular Society
Footnotes
The editors and reviewers of this article have no relevant financial relationships to disclose per the Journal policy that requires reviewers to decline review of any manuscript for which they may have a conflict of interest.
References
- 1.Williams Z.F., Dillavou E.D. A systematic review of venous stents for iliac and venacaval occlusive disease. J Vasc Surg Venous Lymphat Disord. 2020;8:145–153. doi: 10.1016/j.jvsv.2019.08.015. [DOI] [PubMed] [Google Scholar]
- 2.Raju S., Neglen P. High prevalence of nonthrombotic iliac vein lesions in chronic venous disease: a permissive role in pathogenicity. J Vasc Surg. 2006;44:136–143. doi: 10.1016/j.jvs.2006.02.065. discussion 44. [DOI] [PubMed] [Google Scholar]
- 3.Schleimer K., Barbati M.E., Grommes J., et al. Update on diagnosis and treatment strategies in patients with post-thrombotic syndrome due to chronic venous obstruction and role of endovenous recanalization. J Vasc Surg Venous Lymphat Disord. 2019;7:592–600. doi: 10.1016/j.jvsv.2019.01.062. [DOI] [PubMed] [Google Scholar]
- 4.Eklof B., Rutherford R.B., Bergan J.J., et al. Revision of the CEAP classification for chronic venous disorders: consensus statement. J Vasc Surg. 2004;40:1248–1252. doi: 10.1016/j.jvs.2004.09.027. [DOI] [PubMed] [Google Scholar]
- 5.O'Donnell T.F., Jr., Passman M.A., Marston W.A., et al. Management of venous leg ulcers: clinical practice guidelines of the Society for Vascular Surgery (R) and the American Venous Forum. J Vasc Surg. 2014;60(2 Suppl):3S–59S. doi: 10.1016/j.jvs.2014.04.049. [DOI] [PubMed] [Google Scholar]
- 6.Salem A.M., AbdelAzeem AboElNeel H., Fakhr M.E. Long-term outcome of dedicated venous stents in management of chronic iliofemoral obstruction. J Vasc Surg Venous Lymphat Disord. 2022;10:52–59. doi: 10.1016/j.jvsv.2021.04.018. [DOI] [PubMed] [Google Scholar]
- 7.Morris R.I., Pouncey A.L., Quintana B., et al. Quality of life outcomes for patients undergoing venous stenting for chronic deep venous disease. J Vasc Surg Venous Lymphat Disord. 2021;9:1185–11892.e2. doi: 10.1016/j.jvsv.2021.01.009. [DOI] [PubMed] [Google Scholar]
- 8.Shamimi-Noori S.M., Clark T.W.I. Venous stents: current status and future directions. Tech Vasc Interv Radiol. 2018;21:113–116. doi: 10.1053/j.tvir.2018.03.007. [DOI] [PubMed] [Google Scholar]
- 9.Hejazi M., Sassani F., Gagnon J., Hsiang Y., Phani A.S. Deformation mechanics of self-expanding venous stents: Modelling and experiments. J Biomech. 2021;120 doi: 10.1016/j.jbiomech.2021.110333. [DOI] [PubMed] [Google Scholar]
- 10.Chick J.F.B., Abramowitz S.D., Osher M.L., et al. Radiographic findings of distressed venous stents and inferior vena cava filters: clinical implications. AJR Am J Roentgenol. 2017;209:1150–1157. doi: 10.2214/AJR.16.17750. [DOI] [PubMed] [Google Scholar]
- 11.Jayaraj A., Fuller R., Raju S., Stafford J. In-stent restenosis and stent compression following stenting for chronic iliofemoral venous obstruction. J Vasc Surg Venous Lymphat Disord. 2022;10:42–51. doi: 10.1016/j.jvsv.2021.06.009. [DOI] [PubMed] [Google Scholar]
- 12.Saleem T., Raju S. An overview of in-stent restenosis in iliofemoral venous stents. J Vasc Surg Venous Lymphat Disord. 2022;10:492–503.e2. doi: 10.1016/j.jvsv.2021.10.011. [DOI] [PubMed] [Google Scholar]
- 13.Saleem T., Barry O., Thaggard D., Peeples H., Raju S. Iliac vein stent failure in community practice and results of corrective reinterventions. J Vasc Surg Venous Lymphat Disord. 2023;11:525–531.e3. doi: 10.1016/j.jvsv.2022.12.007. [DOI] [PubMed] [Google Scholar]
- 14.Hoshino Y., Yokoi H. Angioscopic evaluation after venous stents. J Vasc Surg Venous Lymphat Disord. 2023;11:136–142. doi: 10.1016/j.jvsv.2022.05.017. [DOI] [PubMed] [Google Scholar]
- 15.Fu J., Tang B., Wang H., Luo H. Stent characteristics of 32 patients with early (<14 days) iliofemoral stent occlusion. J Vasc Surg Venous Lymphat Disord. 2021;9:881–887. doi: 10.1016/j.jvsv.2020.10.011. [DOI] [PubMed] [Google Scholar]
- 16.Powell T., Raju S., Jayaraj A. Comparison between a dedicated venous stent and standard composite Wallstent-Z stent approach to iliofemoral venous stenting: intermediate-term outcomes. J Vasc Surg Venous Lymphat Disord. 2023;11:82–90. doi: 10.1016/j.jvsv.2022.05.012. [DOI] [PubMed] [Google Scholar]
- 17.Jayaraj A., Noel C., Kuykendall R., Raju S. Long-term outcomes following use of a composite Wallstent-Z stent approach to iliofemoral venous stenting. J Vasc Surg Venous Lymphat Disord. 2021;9:393–400.e2. doi: 10.1016/j.jvsv.2020.08.020. [DOI] [PubMed] [Google Scholar]
- 18.Cheng C.P., Suh G.Y., Jalaie H., Barbati M.E. Stent deformations in the common iliac and iliofemoral veins as a result of hip flexion and extension. J Vasc Surg Venous Lymphat Disord. 2023;11:1014–1022. doi: 10.1016/j.jvsv.2023.02.010. [DOI] [PubMed] [Google Scholar]
- 19.Saleem T., Raju S. Comparison of intravascular ultrasound and multidimensional contrast imaging modalities for characterization of chronic occlusive iliofemoral venous disease: a systematic review. J Vasc Surg Venous Lymphat Disord. 2021;9:1545–15456.e2. doi: 10.1016/j.jvsv.2021.03.022. [DOI] [PubMed] [Google Scholar]
- 20.Raju S., Walker W., Noel C., Kuykendall R., Jayaraj A. The two-segment caliber method of diagnosing iliac vein stenosis on routine computed tomography with contrast enhancement. J Vasc Surg Venous Lymphat Disord. 2020;8:970–977. doi: 10.1016/j.jvsv.2020.02.021. [DOI] [PubMed] [Google Scholar]