PICS~AICS

Author: David Bloom, MD., David Balzer, MD

How I do it: Tips, Tricks, and Techniques

A PICS Society education series

Internal PA banding ("Flow Restrictors")

 

Introduction:

Pulmonary artery banding (PAB) is a technique used to control pulmonary blood flow in patients with complex single ventricle anatomy, or patients who will require complex biventricular repairs later in infancy to reduce surgical mortality. Although historically a surgical procedure, a transcatheter approach to internal PAB has been shown to be feasible. The first reports of transcatheter stage I palliation using a modified Amplatzer device were published in 2001 [1], however the concept of transcatheter PAB or pulmonary flow restrictors (PFR) continues to be an area of ongoing research. The use of modified Microvascular Plugs (MVP) (Medtronic Inc., Minneapolis, MN) was first reported in a swine model in 2019 [2]. This study demonstrated the feasibility of using the modified MVP for PFR. Importantly, the study demonstrated that this technique allowed for transcatheter retrieval of the device up to 9-12 weeks following implantation, without significant distortion of the pulmonary artery (PA) anatomy. There have been small cases series (Giessen, Germany, Washington University in St. Louis) [3, 4] reporting the use of a modified MVP for PFR with mixed results. With further development of technique and expansion of use, it is possible that transcatheter PFR using the widely available MVP will be a legitimate option for patients with single ventricle physiology, or high risk two ventricle patients with pulmonary overcirculation.

Anticipated challenges of the procedure:

• Device positioning: may jail upper branch of PA (although this is typically not an issue since the distal portion of the device is uncovered) or migrate distally in PA after device release therefore appropriate device sizing is critical.


• Retrieval: Snares should be available in case retrieval is necessary. Retrieval may be possible up to 12 weeks after the procedure [2]


• Thrombosis: Although this has not been an issue in our experience, the patient should be heparinized for the procedure and antiplatelet therapy should be considered following device deployment.

 

TIP 1. Planning and Preparation

1. Access

4 or 5 fr venous access (typically femoral) is required for this procedure

2. Imaging

Baseline echocardiogram and CXR should be reviewed prior to the procedure.

Additional imaging is not required. If a CTA is obtained, this can be used to estimate the size of the MVP

3. Multidisciplinary Discussion

Discussion with cardiology, cardiothoracic surgery, anesthesia, etc. is important to review indications for procedure, and all additional options for each case.

 

Tip 2. Tools needed

1. Sheaths

4 or 5 fr venous access (typically femoral) is required for this procedure

2. Catheters

4 or 5 fr catheters such as a cobra, JR 2 coronary catheter or an angled glide catheter

1. The MVP 5Q, and 7Q can be delivered through a 4F catheter (recommended inner diameter (ID) of 0.027" and 0.041" respectively).
2. The MVP 9Q will require a 5F catheter (recommended ID of 0.043").

3. Devices

5Q, 7Q, and 9Q MVP device. These devices will need to be modified to create a fenestration. This is done by removing a portion of the PTFE membrane as described by Khan, et al (2) or by using an eye bovie as described by Nageotte et al (4). Our recommendation is to create a hole no larger than 3 mm in diameter. (Figure 1)

 

Tip 3. How I do it

1. Details of the individual tip and technique

Obtain femoral venous access using 4fr or 5 fr sheath

Using a JR-2 or cobra catheter and 0.035 Hi Torque Floppy wire, position catheter into the MPA.

Perform angiogram in MPA to delineate PA anatomy and obtain measurements

Select MVP device based on measurements. We recommend oversizing the device to reduce the likelihood of distal device migration. For pulmonary arteries < 4.5 mm use a 5Q device, >4.5-6.5 mm use 7Q device, >6.5-8.5 mm use 9Q.

Using Eye Bovie, cauterize 2-3mm hole in side cell of device

Position catheter in selected PA and deploy device in proximal pulmonary artery. We have found that the device frequently appears to jail upper lobe branches on angiography, however there is continued flow as the distal portion of the MVP is uncovered. (Figure 2)

Contrast injections through the delivery catheter prior to device release are used to assist in positioning.

Release device from delivery cable and perform angiogram to confirm device position

Repeat process on contralateral PA

Echocardiography should be used at time of procedure to evaluate velocity of flow into branch PAs. (Ideally > 3.0 M/sec with diastolic continuation). This should be performed prior to release of the device so that they may be modified if they are not restrictive enough. This is a critical step in the process.

Post Procedure imaging includes CXR and Echocardiogram

2. Pitfalls to avoid

The device may have a tendency to migrate distally which may jail side branches, or expose proximal arteries to high pressure [4] (Figure 3)

In the study by Khan et al., only 50% of the devices were retrievable via catheter approach at 12 weeks after insertion. It is unclear how long the device can be in place and still be removed in the cath lab or at time of surgery.

Undersizing, or creating too big of a hole in the MVP may not prevent pulmonary over-circulation. This can be avoided with the use of echocardiography during the procedure

Maintaining position of the delivery catheter during device deployment can be challenging. A long sheath positioned in the MPA can be used to support the delivery catheter.

 

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

We have experienced device migration into the distal PA, as well as jailing of branches off of the PA, and this may require device retrieval and re-implantation acutely, or at a later time. Device retrieval is possible using an Amplatz Goose Neck Snare (Medtronic Inc, Minneapolis, MN) by capturing the proximal radiopaque marker on the MVP.

In our experience, despite attempts at creating a small hole in the modified MVP to limit pulmonary blood flow, some patients are still exposed to a significant left to right shunt, leading to pulmonary overcirculation and high mean PA pressure necessitating additional intervention (replacement of MVP) and/or medical management. This can be avoided by intraprocedural echocardiography to ensure that the PFRs are adequately restrictive prior to leaving the cath lab.

After removal of the MVP either transcatheter or at time of surgical intervention, it is possible that there will be stenosis and deformation of the branch PA anatomy (Figure 4) requiring catheter intervention and stenting.

 

Summary:

The use of transcatheter PFRs has the potential to allow for a totally percutaneous stage I approach in patients with single ventricle anatomy, and may allow for delaying surgical intervention in complex biventricular repairs in patients at high risk due to weight, age, or complex anatomy. There is limited data on the use of the modified Medtronic MVP, however it has proven to be a feasible quality option due to its accessibility and relative ease of use. Operators should be aware of the challenges and potential complications related to this procedure as described above. Ongoing research and development is necessary to further perfect the technique and devices used for this transcatheter procedure; additional studies comparing surgical PAB and transcatheter PFR are warranted as well.  

 

References:

1. Chan, K.C., C. Mashburn, and M.M. Boucek, Initial transcatheter palliation of hypoplastic left heart syndrome. Catheter Cardiovasc Interv, 2006. 68(5): p. 719-26.
2. Khan, A.H., et al., Utility of the Medtronic microvascular plug as a transcatheter implantable and explantable pulmonary artery flow restrictor in a swine model. Catheter Cardiovasc Interv, 2019. 93(7): p. 1320-1328.
   
3. Schranz, D., et al., Hypoplastic Left Heart Stage I: No Norwood, No Hybrid. Circulation, 2020. 142(14): p. 1402-1404.
   
4. Nageotte, S., et al., Total Transcatheter Stage 1: A Word of Caution. Pediatr Cardiol, 2021. 42(6): p. 1410-1415.

 

figures

Figure 1. Modified Medtronic Microvascular Plug (MVP). A. Modification of one PTFE cell on inflow portion of device using low temperature fine tip Eye Bovie (Symmetry Surgical, Antioch, TN) cautery device to create 2-3mm hole. B. This example demonstrates the location and size of hole on MVP device.

Figure 2. Angiographic evaluation of flow restrictors two weeks following placement. The PFR in the RPA jails the right upper pulmonary artery (RUPA), however this image demonstrates continued flow into the RUPA.

Figure 3. A. Angiographic evaluation of PFRs through a long sheath in the MPA. This first image better demonstrates jailing of the left upper pulmonary artery, with continued flow of contrast into this branch. B. This image demonstrates jailing of the right upper pulmonary artery. There is still flow seen entering this branch.  

Figure 4. Angiographic evaluation of pulmonary arteries following comprehensive stage II palliation and surgical removal of PFRs. A. Angiogram in SVC demonstrates mild proximal RPA distortion, and moderate to severe LPA stenosis. B. Angiogram performed following 7mm stent placement in LPA showing significant angiographic improvement.