Stent unzipping using an ultra-high-pressure balloon: in vitro and animal experiments

Failure to post-dilate BeSmooth peripheral stents to adult vessel size diameters during benchside tests

BACKGROUND

Low-profile stent implantation remains a rescue treatment for aortic coarctation and branch pulmonary arteries stenosis in small children. Stent re-expansion to cope with vascular growth remains problematic.

OBJECTIVES

To evaluate ex vivo feasibility and mechanical behaviour of over-dilating BeSmooth peripheral stents (Bentley InnoMed, Germany).

METHODS

Three BeSmooth peripheral stents in diameters of 7, 8, and 10 mm were dilated to nominal pressure and then 13 atm. BeSmooth Ø7 × 23 mm was sequentially post-dilated using 12, 14, and 16 mm high-pressure balloons. BeSmooth Ø10 × 57 mm was post-dilated with a 14 mm balloon and then with a 48 mm bare-metal Optimus XXL stent hand-mounted on a 14 mm balloon (stent-in-stent). BeSmooth Ø8 × 57 mm was directly post-dilated with a 48 mm bare-metal Optimus XXL stent hand-mounted on a 16 mm balloon (stent-in-stent). The stents' diameter and length were measured. Digital inflation pressure was noted. Balloon rupture and stent fracture patterns were closely evaluated.

RESULTS

At 20atm pressure, BeSmooth Ø7 × 23 mm shortened to 2 mm forming a 12 mm diameter solid ring circle and the woven balloon ruptured radially. At 10 atm pressure, BeSmooth Ø10 × 57 mm fractured longitudinally in various dispatched breaking points at a diameter of 13 mm without shortening and ruptured the balloon with multiple pinholes. At 10 atm pressure, BeSmooth Ø8 × 57 mm fractured centrally at three different points at a diameter of 11.5 mm without shortening and the balloon broke radially in half.

CONCLUSIONS

In our benchmark tests, extreme shortening, severe balloon rupture, or unpredictable stent fracture patterns at small balloon diameters limits safe post-dilation of BeSmooth stents beyond 13 mm. BeSmooth stents are not ideal candidates for off-label stent interventions in smaller patients.

A novel approach to place an adult-size stent to treat coarctation of the aorta using small introducers: "Nijres technique"

Aortic arch stent placement in young children is a medical dilemma. This is attributed to the critical lack of commercially available stents that can be delivered through small sheaths and yet have the potential to be dilated to the adult-size aorta. Here in, we describe an innovative first-in-human technique that allows for overcoming the aforementioned challenges. A Palmaz Genesis XD stent was placed to treat coarctation of the aorta in two young children through small-bore sheaths.

Ultra-high pressure balloon angioplasty for pulmonary artery stenosis in children with congenital heart defects: Short- to mid-term follow-up results from a retrospective cohort in a single tertiary center

Objective

Balloon angioplasty (BA) has been the treatment of choice for pulmonary artery stenosis (PAS) in children. There remains, however, a significant proportion of resistant lesions. The ultra-high pressure (UHP) balloons might be effective in a subset of these lesions. In this study, we analyzed the safety and efficacy with short- to mid-term follow-up results of UHP BA for PAS in children with congenital heart defects (CHD) in our center.

Methods

This is a retrospective cohort study in a single tertiary heart center. Children diagnosed with PAS associated with CHD were referred for UHP BA. All data with these children were collected for analysis with updated follow-up.

Results

A total of 37 UHP BAs were performed consecutively in 28 children. The success rate was 78.4%. A significantly (P = 0.005) larger ratio of the balloon to the minimal luminal diameter at the stenotic waist (balloon/waist ratio) was present in the success group (median 3.00, 1.64-8.33) compared to that in the failure group (median 1.94, 1.41 ± 4.00). Stepwise logistic regression analysis further identified that the balloon/waist ratio and the presence of therapeutic tears were two independent predictors of procedural success. The receiver operating characteristic curve revealed a cut-off value of 2.57 for the balloon/waist ratio to best differentiate success from failure cases. Signs of therapeutic tears were present in eight cases, all of whom were in the success group. Perioperative acute adverse events were recorded in 16 patients, including 11 pulmonary artery injuries, three pulmonary hemorrhages, and two pulmonary artery aneurysms. During a median follow-up period of 10.4 (0.1-21.0) months, nine cases experienced restenosis at a median time of 40 (4-325) days after angioplasty.

Conclusions

The UHP BA is safe and effective for the primary treatment of PAS in infants and children with CHD. The success rate is high with a low incidence of severe complications. The predictors of success are a larger balloon/waist ratio and the presence of therapeutic tears. The occurrence of restenosis during follow-up, however, remains a problem. A larger number of cases and longer periods of follow-up are needed for further study.

Preliminary testing and evaluation of the renata minima stent, an infant stent capable of achieving adult dimensions

Objectives

This study sought to obtain in vivo data on a new stent and delivery system specifically designed for implantation in infants with the ability to be enlarged to adult dimensions.

Background

There are no endovascular stents designed for or approved for use in infants, nor is there a stent capable of being implanted at infant vessel diameters and achieving adult size while maintaining structural integrity. The Minima stent was designed to address these needs.

Methods

This study was performed in 6 piglets who underwent implantation of 22 Minima stents into the following locations: aorta (n = 11), branch pulmonary arteries (n = 6), and central veins (n = 5).

Results

Successful deployment occurred in 21/22 attempts. Two instances of post‐deployment migration occurred. Stents were re‐expanded at 1, 2, 3 and 5 months after implant. All stents regardless of location could be re‐dilated to the intended diameter to keep pace with somatic growth (implant diameter 6.9 +/− 1.2 mm; final diameter 16.1 mm +/− 1.4 mm). Histopathology at 1 and 5 months demonstrated widely patent vessel lumens with stent apposition to vessel wall, early mild inflammatory response surrounding stent struts, typical vascular damage and healing response to acute dilation and a progressive smooth neointimal growth covering stent struts over time.

Conclusions

In this in vivo study of the Minima stent, there was high implant success, predictable re‐dilatability to adult diameters and favorable histopathology. Further study is warranted.

Mechanical properties of low-diameter balloon expandable covered stents

OBJECTIVES

To determine over-dilation potential of commercially available covered stents.

BACKGROUND

Covered stents including the Atrium iCast, Gore VBX, and Lifestream stents (LS) can treat ruptures, dissections, and aneurysms in small vessels. Especially in growing patients, stents often require serial dilations beyond their implant or nominal diameters. Tolerance of serial dilations is clinically important information for interventionalists.

METHODS

Serial dilations of 5-12 mm iCast, VBX, and LS covered stents were performed in 1-2 mm increments (up to 20 mm). With each dilation, foreshortening and recoil were measured, and stent strut and covering integrity were assessed. High-pressure balloons were used to expand the stents until they fractured or could not be further expanded.

RESULTS

The 5-8 mm LS tolerated dilation to 14.5-16 mm. The 10-12 mm LS stents tolerated dilation to 18 mm and fractured on the 20 mm balloon. LS stents foreshortened 35%-45% on average after 8 mm of over-dilation and had 5%-10% recoil on <6 mm over-dilation. All iCast stents tolerated dilation to 12-13 mm and required fracture for dilation to >14 mm. ICast stents foreshortened 19%-29% at maximum dilation, with 3-6% recoil on <2 mm over-dilation, and < 3% thereafter. VBX stents over-dilated to 2.9-4.7 mm above nominal, foreshortening 40%-50% after 4-6 mm of over-dilation before collapsing into a ring. VBX stent recoil was <2.5% on all dilations.

CONCLUSIONS

LS stents had the greatest over-dilation potential. VBX stents had the least recoil but tended to foreshorten significantly 3-4 mm above nominal. Regardless of nominal size, all iCast stents (including the 5 mm) tolerated dilation to a maximum of 12-13 mm.