Venous Dedicated Stents: How They are Shaping the Vascular Frontier of Venous Disease?

CHRONIC VENOUS obstructive disease is common. Though rarely a cause for mortality or limb loss, it can be devastating for a patient’s quality of life. Advances in endovascular therapy for chronic venous obstructive disease of the iliofemoral and iliocaval segment have surged in recent years. Technological advancements spur improvement in technique and vice-versa, leading to significant improvements in efficacy and safety of these interventions over short periods of time. The rise of intravascular ultrasound (IVUS) to gold-standard status for intraoperative venous imaging highlights this point.

Deep and central venous intervention demands painstaking attention to detail. In order to translate technological advances into real-world, clinical outcomes, operators must be intimately familiar with the available devices and techniques.

For several years, options for stents in the venous arena were limited to off-label use of the Wallstent endoprosthesis (Boston Scientific Corporation) and off- label use of the Gianturco Z-stent (Cook Medical). The Wallstent is a self-expanding, stainless-steel stent with a closed cell design.1 It is the most well-studied stent in the venous space and has excellent conformability with intermediate radial force and compression resistance in the main body (mid-portion) of the stent.

The limitations of the Wallstent design are also well understood. Due to the location of May-Thurner lesions, only the weaker distal ends of a Wallstent may contact the site of extrinsic compression, resulting in inadequate radial force and requiring buttressing with a Z-stent.2 A poor alternative would be to land the Wallstent in the inferior vena cava in order to expose the site of venous compression to the stronger mid portion of the stent. This technique can result in “jailing” of the contralateral iliac vein, increasing the risk for contralateral acute DVT by up to 10%.3,4 The Wallstent can be difficult to deploy accurately due to unpredictable foreshortening upon expansion.

Several dedicated venous stent platforms have received FDA approval for use in the United States in the past two years: Venovo (BD International), Vici (Boston Scientific Corp.), Zilver Vena (Cook Medical), and Abre (Medtronic). All systems are self-expanding and utilize non-braided nitinol construction. One of the principal differences lies in the stent matrix design; Venovo, Zilver Vena, and Abre are open-cell designs while the Vici stent uses a closed-cell layout.5,6,7,8

How We Do It

Since the introduction of these new stent platforms, we have mainly used the Venovo system. Our multidisciplinary vascular practice handles a high volume of straightforward and complex iliofemoral and iliocaval venous disease. The Venovo system is our go-to venous stent for several reasons. The deployment mechanism and open-cell design allow for simple and accurate deployment with minimal foreshortening. The Vici stent, on the other hand, undergoes approximately 20% foreshortening upon expansion to nominal diameter.8

Typically, open-cell stent matrices favor conformability and precise deployment, while closed-cell designs tend to impart greater radial force and resistance to external compression. We have found that the Venovo stent strikes an acceptable balance between conformability and radial strength while maintaining relative ease of accurate deployment. We observed that the need for reintervention on these patients has decreased with an increase in precise disease identification and proper vein sizing with intravascular ultrasound technology, along with utilization of the venous dedicated platform of BD Venovo stent system.

Limitations of Currently Available Venous Stents

Disease extending to the iliocaval confluence and up the inferior vena cava (IVC) are often encountered and represent an area of current unmet need. Double-barrel stenting inherently creates mal-apposition, with turbulent, potentially thrombogenic flow patterns within the leftover “gutters” between the stents. This technique also results in competing radial force between the two stents at the level of the confluence and IVC, often leading to a compromised luminal diameter of one of the stents.

Culotte, crush, and other bifurcation stenting techniques commonly used in the coronary arteries are relatively under-explored in the central venous space. Culotte-style stenting in the iliocaval confluence would involve deploying the first stent from the iliac vein across the confluence into the IVC, temporarily excluding the contralateral iliac vein. This is followed by delivery and deployment of a second stent from the contralateral side through an appropriately located interstice of the existing stent. This creates a common stent lumen in the IVC, with likely improved wall apposition, reduction in radial force competition and elimination of turbulence- inducing, peri-stent “gutters” seen in kissing stent configurations. Note that this technique is unsuitable for closed-cell stent designs due to risk of significant napkin-ring constriction at the site of interstice crossing.

Regarding sizing, the Vici and Zilver Vena systems are indicated for reference vessel diameters up to 15mm, unsuitable for (off-label) deployment in the IVC.6,8 Venovo and Abre stents can be used with reference vessel diameters up to 19mm; however, they will likely still be undersized for most IVCs.5,7 Note that deployment of any other newer-generation venous stents in the IVC constitutes off-label use.

What the Future May Hold

A renaissance of venous intervention and device development has begun. Nonetheless, significant work in both technique and device technology still needs to be done to resolve the limitations of currently available venous stent platforms.

Outstanding results have been achieved with Wallstent and Z-stents, but further refinement and validation of technique would help to advance our understanding of venous stenting and the therapies we are able to offer. Z-stents have potential, providing a competitive option for venous disease management, but they are due for an update to match our current knowledge of venous disease, particularly for disease extending into the iliocaval confluence up the IVC.

An uncovered, short bifurcated stent design, likened to an EVAR bifurcated body stent without graft fabric available in wide diameters may be developed for improved stenting at the iliocaval confluence. Apart from avoiding radial force competition seen with kissing stents, the design may obviate issues such as entanglement of stent struts that create irregular luminal surfaces. These irregular surfaces produce turbulent flow with theoretically increased risk of excess thrombus formation. In addition, unpredictable point-loading of force on the stent structure and venous wall impart a theoretically increased risk of late-stent failure.

Ultimately, investigation and validation of innovative techniques using currently available devices represent the most efficient way forward for the ongoing venous “renaissance,” and the introduction of the current dedicated venous stent systems represents a strong launching pad for such advancement.