PICS~AICS

Authors: Nicholas Robles, MD, Abhay Divekar, MD, FPICS, FSCAI
UT Southwestern Medical Center, Dallas Children’s Hospital, Dallas, TX

How I do it: Tips, Tricks, and Techniques

A PICS Society education series

Tips and Tricks for Creating a Controlled Shunt Using a Diabolo Stent Configuration

Introduction:

Increasingly, we are faced with the need for creating a controlled shunt across the atrial septum or across the Fontan baffle, and there are no commercially available devices in the United States. Utilizing a diabolo (dumbbell shaped) stent design has been a successful strategy to create a controlled opening for shunting while simultaneously minimizing the risk of stent embolization. Once created, the size of the shunt can be dialed (increased) as clinically indicated. This stent design can be tailored to patient specific anatomy. 

A variety of methods have been described to create the diabolo shape. The fundamental technique is to dilate the chosen stent on an intentionally oversized balloon while restricting the center of the stent to create the diabolo design. The central constriction can be achieved by weaving a suture through the cells at the center of the stent, restricting the center of the oversized angioplasty balloon using a pacing wire or snare (our technique), or externally restricting the center of the stent with a snare (1-4). All methods have their own advantages and limitations. We have successfully adapted and reported a simplified technique to create the diabolo configuration, and this will be discussed in detail with particular attention to the technical aspects of the procedure (1). The method utilizes equipment available in most congenital catheterization laboratories. 

Anticipated challenges of the procedure:

  • Mount the snare onto the angioplasty balloon while maintaining the central position of the snare while the stent is crimped onto the balloon.
  • The techniques used to create the central constriction has the potential to be overwhelmed when high inflation pressures are used. This creates two problems, the shunt is no longer controlled (unacceptably large), and is unstable increasing risk for embolization.

    • TIP 1. Planning and Preparation

    1. Access: Usually femoral vein

    2. Imaging: Pre-procedure transthoracic echocardiogram is routinely available. Intraprocedural transesophageal echocardiography is very useful to guide the transseptal/transbaffle puncture and to assess adequacy of the controlled shunt.


     Tip 2. Tools needed

    1. Long sheath
    • The delivery sheath should be 2-3Fr larger than that recommended for the balloon angioplasty catheter alone. The snare does not significantly increase the crossing profile and therefore typically 2Fr larger sheath is adequate.

    1. Stent characteristics
  • Choose a stent that can be dilated to large diameter (18 mm or larger). Pre-mounted small diameter stents are not suitable.
  • Choose a stent with the lowest crossing profile.
  • Avoid open cell design as this increases the potential for snare entrapment and suboptimal snare placement. It is also difficult to remount the stent after pre- dilation.
  • Choose a malleable stent, a stent with high radial strength is not needed.
  • Stent length should consider the anticipated shortening resulting from intentional flaring of both ends.
  • Covered stents can be used. However, in situations such as Fontan fenestration or atrial septal stenting, the stent cover may impede flow into or around the proximal end of the diabolo stent. This can be particularly problematic when the stent orientation is orthogonal to the direction of flow, as in the case of Fontan fenestration stenting. If a covered stent is chosen, the covering should fully encapsulate the stent.

    • Based on these characteristics, we have found that the Palmaz Genesis XD stent series satisfies all the requirements.

    1. Angioplasty catheter/balloon
  • The balloon chosen for stent deployment should be intentionally longer than that necessary for stent deployment (for example, when using a Genesis XD 1910 stent choose a balloon that is 3-4 cm in length based on patient anatomy).
  • Balloon diameter should be at least 2 times the desired final defect diameter. This allows for adequate flaring of the ends to maintain the diabolo design.

    1. Central constricting mechanism
  • A 5 mm Gooseneck Snare kit (any vendor)

    • Tip 3. How I do it – please review videos for narrated summary

    1. Mount and pre-dilate a Genesis XD stent on an 8 mm angioplasty catheter to open the stent to a uniform size. Dilating the stent to 8 mm increases the ease with which the stent can be mounted on the central snare.
    2. Center the 5-mm snare on the chosen balloon based on criteria mentioned above and appropriate for patient anatomy.
    3. Use the included snare catheter or microcatheter to maintain the snare in the closed and circular position at the center of the balloon.
    4. Start to manually crimp the stent from the patient (distal) end of the stent and work proximally. Once the stent is mounted, the snare catheter is slowly removed while crimping the center making sure that the snare remains in an orthogonal, circular configuration. This is best accomplished by two trained providers.
    5. Under fluoroscopy outside of the body, confirm that the stent is centered on the snare and the balloon length is sufficiently longer than the stent at both ends. Confirm that the snare is coaxial and circular and is not an elongated ellipse (this is necessary to maintain a central waist as the stent is deployed).
    6. Perform transbaffle puncture with or without transesophageal echocardiographic guidance. Remember that there is a potential space between the conduit and the atrium. When the long sheath is advanced, it can tent the atrial wall away from the conduit. It is crucial to ensure that the long sheath is advanced completely into the atrium and not merely tenting the atrial wall. This is easier to appreciate if the potential space is stained during the transseptal puncture. We have found that if there is difficulty in advancing the sheath and dilator, inflating a small diameter balloon greatly facilitates crossing of the sheath as the balloon is deflated.
    7. Advance the assembled stent over the wire to the distal end of the long sheath. Partially unsheathe the stent to the level of the snare. Gently inflate the angioplasty catheter to flare the distal/atrial end of the stent.
    8. Retract the entire system (sheath, distally-flared stent) as a unit so that the atrial wall is tacked to the conduit.
    9. While maintaining steady backward tension, unsheathe the proximal stent and inflate the balloon to form the final diabolo configuration. DO NOT use high pressure otherwise the central constricting mechanism can unravel.
    10. Deflate the balloon. Remove the snare and balloon catheter as a unit and maintain wire position.
    11. Assess patency, desired size, and positioning with pressure and angiographic.
    12. This technique creates a fenestration between 4-5 mm. If a larger diameter is desired, this can be “dial in” simply by dilating the waist with a balloon of desired diameter. It is best to make this decision before removing the wire after initial stent placement.

    Tip 4. What complications to expect and how to deal with them

    1. If the snare is not circular and orthogonal on the angioplasty balloon but instead it is elliptical, it can be difficult to create the waist especially when the septum is thin (e.g. when creating an ASD in the native septum). To minimize this problem, there should be two operators to mount the stent and ensure that the stent/snare is optimized under fluoroscopy.
    2. DO NOT use high pressure during stent deployment. High pressure stent deployment can unravel the snare and result in an inappropriately large fenestration. Even if the waist does not inflate to 5 mm (resistance in the Fontan fenestration), do not use higher pressure with the initial balloon used to create the diabolo stent configuration. Once the shape is created, the stent is stable, choose an appropriate size balloon, e.g. 5 mm diameter and then perform dilation of the waist at the necessary inflating pressure. This will prevent potentially catastrophic oversizing
    3. When transseptal puncture is performed to create a fenestration in an extracardiac Fontan, the atrial wall can be pushed away from the conduit during the puncture or while advancing the long delivery sheath. Once the atrial end of the stent is inflated, the assembly is pulled back to tack the atrial wall against the conduit eliminating the potential space. If this is not done, and the stent is inadvertently deployed, there is risk of stent embolization and/or bleeding into the potential space created. This complication is best treated by prevention. We routinely use echo guidance, angiography through the sheath to ensure sheath position.

    Summary:

    Creating a diabolo stent configuration is simple, reproducible, and utilizes equipment available in most catheterization laboratories. The technique can be easily adapted to meet patient specific requirements. The diabolo stent configuration can be used to create controlled atrial defect for patients with pulmonary hypertension, hypoplastic left heart syndrome, diastolic left heart failure, creation of Fontan fenestration either through the Fontan baffle or through the floor of the pulmonary artery into the pulmonary venous atrium, and finally it can be used to create a flow restrictor in the pulmonary arteries or a systemic to pulmonary artery shunt.

    References:

    1. Aldoss, O., & Divekar, A. (2016). Modified Technique to Create Diabolo Stent Configuration. Pediatr Cardiol, 37(4), 728-733. https://doi.org/10.1007/s00246-015-1339-6
    2. Anderson, B., Bhole, V., Desai, T., Mehta, C., & Stumper, O. (2010). Novel technique to reduce the size of a Fontan Diabolo stent fenestration. Catheter Cardiovasc Interv, 76(6), 860-864. https://doi.org/10.1002/ccd.22661
    3. Prieto, L. R., Latson, L. A., & Jennings, C. (2006). Atrial septostomy using a butterfly stent in a patient with severe pulmonary arterial hypertension. Catheter Cardiovasc Interv, 68(4), 642-647. https://doi.org/10.1002/ccd.20745
    4. Stümper, O., Gewillig, M., Vettukattil, J., Budts, W., Chessa, M., Chaudhari, M., & Wright, J. G. (2003). Modified technique of stent fenestration of the atrial septum. Heart, 89(10), 1227-1230. https://doi.org/10.1136/heart.89.10.1227

     

    VIDEOS

    There are three narrated videos which will demonstrate the steps of creating and deploying the diabolo stent configuration. The first video, “Assembly Video” shows how to mount the stent on the snare. The second video, “"Caution! Snare Unraveling at Higher Pressure" discusses a critical step to avoiding overinflating the central constricting mechanism. The third video, “Deployment Video” shows the steps used to deploy the diabolo stent to create a controlled Fontan fenestration.

    Video 1:

    Video 1: Assembly Video

     

    Video 2:

    Video 2: Caution! Snare Unraveling at Higher Pressure

     

    Video 3:

    Video 3: Deployment Video