Utility of Balloon-Expandable Covered Stent Graft Endoprosthesis in Congenital Heart Disease

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J INVASIVE CARDIOL 2024. doi:10.25270/jic/24.00275. Epub November 7, 2024.

Vascular stenosis can be a significant cause of morbidity and mortality in children with congenital heart disease (CHD).1 Stenotic lesions can be congenital or secondary to prior palliative surgery. Etiology includes scar formation, tension/stretching, or external compression. The risk of developing stenotic lesions increases with the number of repeat sternotomy operations.2 To reduce or delay the need for repeat median sternotomy, transcatheter therapy (balloon angioplasty and/or stent implantation) plays an essential role in management.  For the pediatric interventionalist, stent-based therapy often involves off-label use of existing stents. An optimal product for younger/smaller patients with CHD would incorporate characteristics that include a low delivery profile, a post-dilation capacity that allows for somatic growth, adequate radial strength to resolve stenosis/compression, and a physical covering to minimize potential for vessel disruption. Herein, we describe our early experience with the VIABAHN VBX balloon expandable endoprosthesis (Gore), a premounted, balloon expandable, covered stent graft that encompasses many of these desired features and highlights performance for managing stenotic lesions in patients with CHD, and which has previously been rarely used for children with CHD.

Retrospective chart review was performed to identify all patients who received catheter-based intervention with implantation of the stent graft for intracardiac and/or extracardiac obstructive lesions at Mayo Clinic Rochester between December 1, 2020 and February 8, 2023.  Patients who received this stent graft for creation of an extravascular shunt were excluded (eg, transcatheter reverse Pott’s shunt and systemic to pulmonary artery shunt). We divided the patients into 4 categories according to the location of the obstruction: (1) right ventricular outflow tract obstruction (RVOTO), (2) pulmonary artery stenosis (PAS), (3) systemic vein stenosis (SVS), and (4) coarctation of aorta (CoA). Demographic and procedural data were extracted, and follow-up was captured through 1-year post-implant when present. Continuous data were summarized using mean (SDs) or median (ranges). Categorical data were presented as counts (percentages). All results were considered statistically significant at P ≤ .05 and a CI of 95%. The Statistical Package for the Social Sciences (SPSS v28.0) (SPSS, Inc.) was used for all calculations. The study adheres to the institutional guidelines and, as a retrospective study, consent for the study was waived. All patients/surrogates were informed that this was an off-label use of the stent.  

Demographics and diagnosis

A total of 22 patients (64% female, n = 14) underwent 23 catheterization procedures during which 29 stent grafts were implanted in 26 lesions. The median age was 6.6 years (range 1.3-19.3 years). The majority of the cohort (91%, n = 20) had congenital heart disease, while 2 (9%) patients had stenotic lesions attributed to mediastinal mass. Patient demographics and diagnoses are detailed in Table 1.

Acute outcomes

From a procedural standpoint, general anesthesia was utilized in 17 of the 23 procedures, while monitored anesthesia care was provided for the remaining 6 procedures. The patients typically underwent right heart hemodynamic catheterization, coupled with angiography for those with RVOTO, PAS, and SVS (Figures 1-3, pre). Additional retrograde left heart hemodynamic catheterization and angiography were performed for the patients with CoA (Figure 4, pre). The delivery sheath was as small as 7-French (Fr) in the femoral vein for the patients with RVOTO, PAS, and SVS, and 8-Fr in the femoral artery for patients with CoA, with ultrasound confirmation of a femoral arterial diameter greater than 3 mm prior to access in smaller patients. Stent size and pre-mount balloon diameter were chosen based on targeted pre-/post-stenotic vessel diameter, in addition to minimum waist diameter to allow secure delivery. Length was determined for adequate coverage of the targeted lesion. Rapid right ventricular pacing was performed only for CoA stent implantations. Selective post-implantation dilation with a non-compliant balloon was performed as needed to achieve the targeted diameter. Post-implant ultra-high-pressure dilation (≥ 20 atm) was performed on 8 stent grafts for full expansion (Table 2). Post-implantation angiography (Figure 1-4, post) and hemodynamic measurements were analyzed for all cases (Table 2).

Complications

We observed no major procedural complications, including vascular disruption, dissection, extravasation of contrast, formation of aneurysm/pseudoaneurysm, balloon rupture, or stent migration. Minor vascular access site hematoma occurred in 2 patients; no treatment was needed. 

Follow-up

Twenty out of 22 patients had follow-up; the mean duration was 12 months (range 2.5-33 months). Two international patients had limited early follow-up before returning to their home country. Post-procedure echocardiogram was performed to evaluate the gradient and stent patency. The survival rate was 100%.

A planned reintervention was performed in 4 patients. Of these, 2 occurred 1 year after innominate vein reconstruction in patients with Glenn/Fontan pathways. The other 2 reinterventions were for RVOT stent redilation/re-stenting to accommodate somatic growth in young children. An unplanned intervention was necessary 70 days later in a patient treated for SVS who developed external stent graft distortion and thrombus formation following the placement of a plasmapheresis line. During the reintervention, the stent graft was redilated, successfully resolving the moderate thrombus.

We describe the successful off-label use of a covered stent graft for transcatheter palliation therapy in various types of stenotic vascular lesions, including complete vascular occlusions in a wide variety of patients with CHD and non-CHD. The VIABAHN VBX stent graft was originally designed to treat aortoiliac occlusive disease in adults. Its nominal diameter ranges from 5 to 11 mm and its length ranges from 15 to 79 mm.³ Despite limited diameter/length options for the pediatric population, our team found this stent graft particularly well-suited for addressing multiple types of stenotic lesions in CHD.

One of the appealing features of this stent graft is that it is designed with post-implant dilation capability, an important issue when there is expected somatic growth in addition to anticipated growth in vessel caliber. The stent is currently available in 2 configurations: "normal" and "large". The normal configuration comes in a diameter of 5 to 11 mm and allows dilation of 2 to 3 mm beyond the original graft size, while the large configuration is designed to achieve a diameter of 16 mm post-dilation. Planned re-dilations may be necessary depending on the desired vascular diameter to accommodate somatic growth. In the pediatric population, post-dilation is crucial for managing all stenotic lesions, particularly in cases involving the aorta, RVOT, or pulmonary artery (PA) branches.⁴ The post-implant dilation capability of the large diameter version enables the stent graft to be expanded to accommodate growth. For pediatric patients requiring a valved-RVOT, transcatheter pulmonary valve implantation can be performed in the dilated RVOT to meet appropriate valve size requirements. A diameter of 22 mm or more is the goal for transcatheter pulmonary valve implantation (TPVI). The large configuration stent graft can be further dilated in this setting to achieve a diameter of 20 to 22 mm with re-stenting. However, it is important to note that the in vitro testing of this stent graft has shown significant foreshortening when reaching diameters of 20 to 22 mm.⁵ Further studies and long-term follow-up are necessary to confirm its efficacy and longer-term durability in providing a platform for future transcatheter interventions.

The stent graft is also designed with independent tines rather than a continuous frame, conferring superior flexibility and enabling segmental flaring. This feature is advantageous for trackability over a wire in small pediatric patients, particularly those with branch PA stenosis (Figure 2). In addition, treatment of patients post-LeCompte maneuver may risk the creation of aorto-pulmonary fistula creation, so a covered platform is ideal.⁶ The flexible frame may allow for a more rounded implant shape contouring to the aorta. The non-contiguous frame also allows for segmental flaring; this creates a funnel into the stent that allows for ease of wire passage and entry upon re-intervention. The additional flexibility of this design leads to improved navigation through the calcified or acutely angulated regions of the RVOT, thereby delaying the necessity for surgical intervention in pediatric cases (Figure 1).

The stent graft is pressure-mounted to the balloon, mitigating the risk of stent migration during advancement in addition to providing more low-profile delivery. We typically employed a long sheath for stent graft delivery but noted that passage between vessels did not require the advancement of a sheath prior to stenting, which dramatically reduced the risk of extravascular bleeding. Sheathless delivery enabled the creation of  extravascular shunts, including the Reverse Potts Shunt, for patients with severe pulmonary hypertension,⁷ as well as a venous reconstruction of a chronic superior vena cava (SVC) occlusion that allows primary passage of the stent graft without sheath dilation of the tract.⁸

The low profile of the stent graft is also advantageous for small pediatric patients because it minimizes the risk of access site complications. We have previously detailed the technique for transcatheter palliation for CoA in young children (Figure 4).^4,9 The 8L configuration, pre-mounted on an 8-mm balloon, is designed to go through a 7-Fr sheath. Recently, a new set of lower profile stent grafts has become available, with some designed to go through a 6-Fr sheath.

Lastly, the stent graft is covered with a CBAS-expanded polytetrafluoroethylene graft. This graft material has improved thromboresistance and can reduce intimal hyperplasia, as demonstrated in animal models.^10,11 Neointimal hyperplasia is a major cause of in-stent stenosis,¹² and it can also occur in large vessels after bare metal stent implantation. In small children, even a slight degree of neointimal hyperplasia can significantly impact the patency because of the small size of the treated vessel. Neointimal hyperplasia is triggered by clot formation.¹³ Stents implanted in the venous system or the PA of patients who underwent Glenn/Fontan may be more prone to neointimal hyperplasia due to low blood flow velocity. It is reassuring that we have not observed significant in-stent thrombogenesis in our patients who have been managed with aspirin monotherapy, specifically following systemic venous stent implantation. The 1 stent graft requiring un-planned re-intervention was geometrically altered with a line across the affected region. Therefore, careful attention to stent integrity on radiographic assessment after additional procedures is very important.

Based on our experience, we postulate that there are areas for improvement to make the VIABAHN VBX stent graft better suited for pediatric stenotic lesions. The first potential limitation is its maximum post-dilation diameter of 16 mm. For an adequate adult-sized RVOT or aorta, the post-dilation capacity would be approximately 20 to 22 mm for the aorta and 24 to 26 mm for the RVOT. However, the performance of the current product remains uncertain when fractured and dilated past 22 mm.⁵ Second, for balloons 8 mm or larger, the shortest length is 29 mm when crimped and 17.6 mm at maximum diameter (16 mm). Excessive stent length is problematic in smaller pediatric patients with short landing zones, particularly with a covered stent. For example, excessive length can limit its use in PA stenosis treatment where jailing a distal branch should be avoided.

Limitations

This is a single-center, retrospective study with short follow-up data, and it is limited by selection and ascertainment bias. A multi-center study with long-term follow-up is necessary to reveal long-term issues. Stent frame durability and ability to further expand the stent, even fracturing for larger stent implantation as somatic growth occurs, need further evaluation. More data are needed to determine whether stent-based therapy with this graft aligns with expectations for planned re-interventions for somatic growth or if more unplanned re-interventions will be required.

Overall, our cohort demonstrates promising results for the application of a covered stent graft technology for treating complex or recurrent stenotic lesions and vascular occlusions in patients with CHD. Long-term studies in larger multi-center cohorts will be necessary to compare the outcomes of stent-based treatments in children.

Liwei Yu, MB, PhD¹; Allison K. Cabalka, MD^1,2; Nathaniel W. Taggart, MD^1,2; Donald J. Hagler, MD^1,2; Frank Cetta, MD^1,2; Kaitlyn Krebushevski, DO¹; Trevor J. Simard, MD, PhD²; Alan M. Sugrue, MB, BCh, BAO³; Alexander C. Egbe, MBBS, MPH²; Jason H. Anderson, MD^1,2

From the ¹Department of Pediatric and Adolescent Medicine / Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota; ²Department of Cardiovascular Medicine / Division of Structural Heart Diseases, Mayo Clinic, Rochester, Minnesota; ³Department of Cardiovascular Medicine / Division of Heart Rhythm Service, Mayo Clinic, Rochester, Minnesota.

Disclosures: Dr Cabalka is an investigator for Medtronic, Inc. and a consultant at Edwards Lifesciences and B. Braun Interventional Systems. Dr Anderson serves on the cardiac advisory board for W.L. Gore & Associates and is a consultant for Medtronic, Inc. and Edwards Lifesciences.

The paper’s contents have been presented at the WCPCCS 2023 International Conference.

Address for correspondence: Liwei Yu, MB, PhD, Mayo Clinic Hospital, Saint Marys Campus, 4^th Floor Mary Brigh Building, 1216 2nd St SW, Rochester, MN 55902, USA. Email: yu.liwei@mayo.edu