Various reasons for repeat dilatation of stented pulmonary arteries in paediatric patients

Prolonged recovery of 3D printed, photo-cured polylactide shape memory polymer networks

Shape memory polymers are materials that are able to retain a deformed state until an external stimulus, most typically heat, triggers recovery to the original geometry. Whereas typically, shape memory polymers are required to recover fast (seconds to minutes), many applications, particularly in the medical field, would benefit from a slow recovery (days to weeks). In this work, we exploit the broad glass transition range of photo-cured poly(D,L-lactide) dimethacrylate networks to obtain recovery times of up to 2 weeks, at 11 °C below the peak glass transition temperature of 58 °C. Recovery times decreased considerably for higher recovery temperatures, down to ∼10 min at 55 °C. A large spread in glass transition values (53.3-61.0 °C) was observed between samples, indicating poor reproducibility in sample preparation and, hence, in predicting shape recovery kinetics for individual samples. Furthermore, a staged recovery was observed with different parts of the samples recovering at different times. The ability to prepare complex structures using digital light processing stereolithography 3D printing from these polymers was confirmed. To the best of our knowledge, this work provides the first experimental evidence of prolonged recovery of shape memory polymers.

Role of stents in congenital heart disease

For more than 10 years, balloon-expandable intravascular stents have become an integral part of treatment for obstructive vascular lesions in children and adults with congenital heart disease. The initial problems with stents, such as sharp edges, rigid frame and unacceptable shortening when over-expanded have been overcome to a large extent with the newer designs. The problems related to delivery of stents, such as stent migration, balloon rupture, flaring of the edges of the stent, rupture of vessels and milking of the stent off the balloon, have also been overcome by newer designs of balloons. The failure of growth of balloon-expandable stents with the growth of the child is managed by redilation with or without additional stenting and newer growth stents. Self-expanding stents are not appropriate for use in growing children due to the limitation of their maximum diameters. The development of biodegradable stents may overcome these disadvantages in the future. Various new developments have recently occurred. Covered stents are ideal for treating acute vessel rupture and in isolating vascular aneurysms. Drug-eluting stents may prevent restenosis, but have not been used in children. Valved stents are a recent innovation for the treatment of regurgitant pulmonary valves.

Pulmonary artery stent implantation in children with single ventricle malformation before and after completion of partial and total cavopulmonary connections

OBJECTIVES

Relief of pulmonary artery stenosis before and after cavopulmonary connections (CPC) in patients with single ventricle malformation is essential to optimize pulmonary hemodynamics. We evaluated the risk factors for pulmonary artery stenosis and assessed the outcome after stent implantation.

INTERVENTIONS

Seventeen stents in twelve patients were implanted for pulmonary artery stenosis before and after CPC at a mean age of 4.5 (0.1-17.6) years.

RESULTS

Fourteen stents were placed in the left pulmonary artery (82%) and three stents in the right pulmonary artery (18%). One stent was implanted intraoperatively. Mean time between surgery and stent implantation was 28 (1-132) months. The mean (SD) size of the pulmonary artery stenosis was 3.1 +/- 2.1 mm before and 8.1 +/- 3.3 mm (P < 0.001) after stent implantation. Six out of seventeen stents (35.2%) had to be redilated after a mean time interval of 19 (5-48) months. Two patients' stents were removed during the next surgical procedure; both needed an early restenting of the affected vessel. There were no procedure-related complications for stent implantation or redilatation. Anatomical risk factors for pulmonary artery stenosis were right aortic arch and hypoplastic pulmonary arteries, whereas dilatation of the ascending aorta for LPA stenosis and Blalock-Taussig shunt for RPA stenosis were surgical risk factors.

CONCLUSIONS

Stent implantation to treat pulmonary artery stenosis in pediatric patients with CPC is effective and can be realized safely. Close follow-up is recommended in patients with risk for pulmonary artery stenosis. During total cavopulmonary connection, previously implanted stents at that site should be left in place or be changed in a hybrid procedure to a larger diameter, because the etiology of stenosis may persist after surgery and the surgical removal could result in vessel injury that promotes restenosis.

The role of stents in the treatment of congenital heart disease: Current status and future perspectives

Intravascular or intracardiac stenoses occur in many forms of congenital heart disease (CHD). Therefore, the implantation of stents has become an accepted interventional procedure for stenotic lesions in pediatric cardiology. Furthermore, stents are know to be used to exclude vessel aneurysm or to ensure patency of existing or newly created intracardiac communications. With the further refinement of the first generation of devices, a variety of "modern" stents with different design characteristics have evolved. Despite the tremendous technical improvement over the last 20 years, the "ideal stent" has not yet been developed. Therefore, the pediatric interventionalist has to decide which stent is suitable for each lesion. On this basis, currently available stents are discussed in regard to their advantages and disadvantages for common application in CHD. New concepts and designs developed to overcome some of the existing problems, like the failure of adaptation to somatic growth, are presented. Thus, in the future, biodegradable or growth stents might replace the currently used generation of stents. This might truly lead to widening indications for the use of stents in the treatment of CHD.

Intraoperative Pulmonary Artery Stenting: An Alternative Technique for the Management of Pulmonary Artery Stenosis

BACKGROUND

Pulmonary artery reconstruction remains a challenging clinical problem. We sought to evaluate the use of intraoperative stenting in conjunction with open heart surgical repairs.

METHODS

We retrospectively analyzed data from 22 patients between 1998 and 2003 who underwent intraoperative pulmonary artery stenting.

RESULTS

The mean age was 9.3 years (range, 9 months to 24 years). The left pulmonary artery was stented in 8 patients, the right in 13, the main in 1, and bilateral in 1. Available echocardiograms in 20 patients revealed a mean preoperative diameter of 7.6 mm (range, 3 to 16.5 mm) and a mean peak gradient of 45.4 mm Hg (range, 20 to 120 mm Hg). Augmentation patch angioplasty of the contralateral pulmonary artery was performed in 11 patients. Thirteen patients had pulmonary valve replacement and 11 had conduit replacement or augmentation. Three patients underwent tricuspid valve repair, 6 had Fontan, and 4 underwent a modified Maze procedure. Follow-up echocardiograms demonstrated a decrease in mean peak gradient to 4.3 mm Hg (range, 0 to 15 mm Hg), a change in mean peak gradient of 41.1 mm Hg (93% reduction). After stenting the mean pulmonary artery diameter increased to 10.9 mm (range, 6 to 17.9 mm). There was no perioperative mortality. At a mean follow-up of 22.8 months (range, 6 to 57 months), there were no surgical or percutaneous reinterventions.

CONCLUSIONS

Intraoperative pulmonary artery stenting is a safe and effective technique that can be used as an alternative to patch angioplasty. Close follow-up is needed to examine the long-term outcome of this procedure, with special attention to the growth and development of the stented vessel.

Implantation of endovascular stents for the obstructive right ventricular outflow tract

OBJECTIVES

To evaluate the effectiveness and long term outcomes of catheter intervention for obstructive conduits between the right ventricle and pulmonary arteries.

DESIGN

Retrospective chart review.

SETTING

Tertiary care paediatric cardiology unit.

PATIENTS AND INTERVENTIONS

70 procedures in 68 children (median age at intervention 6 years, median interval after conduit insertion 3.4 years) were analysed. All children had haemodynamic indications for conduit replacement. Twenty four children underwent a second intervention (stent dilatation in 17, second stent implantation in seven).

RESULTS

Mean (SD) conduit pressure gradient decreased from 44 (18) mm Hg to 18 (12) mm Hg at the initial intervention (n = 62, p < 0.001) and from 39 (15) mm Hg to 23 (10) mm Hg at the second intervention (n = 16, p < 0.001). The percentage of the predicted right ventricular outflow area increased from 17 (9)% to 44 (22)% at the initial intervention (n = 62, p < 0.001) and from 24 (8)% to 29 (11)% at the second intervention (n = 21, p < 0.001). The conduit was subsequently replaced in 33 children. Freedom from conduit replacement from the time of stent implantation was 83%, 75%, and 47% at one, two, and five years, respectively, and from the time of the initial conduit surgery it was 87%, 64%, and 42% at five, eight, and 10 years, respectively. Body growth was maintained, no deaths were reported during follow up, and pulmonary insufficiency was well tolerated.

CONCLUSION

A catheter treatment strategy for obstructive conduits is safe and effective in prolonging conduit function.

The CP stent--short, long, covered--for the treatment of aortic coarctation, stenosis of pulmonary arteries and caval veins, and Fontan anastomosis in children and adults: an evaluation of 60 stents in 53 patients

OBJECTIVE

To evaluate the feasibility and usefulness of the Cheatham platinum (CP) stent in a broad spectrum of lesions.

METHODS

Retrospective analysis of 60 implanted CP stents (11-80 mm lengths, 12 covered) between September 2001 and March 2004.

PATIENTS

53 patients aged 2.5-68 years (median 17 years). Body weight ranged from 12-95 kg (median 52 kg). Thirty six patients had aortic (re)coarctation; seven of them had functionally interrupted aortic arches. Thirteen patients had pulmonary artery stenosis and four had stenosis of caval veins or conduits in a total cavopulmonary connection (TCPC).

RESULTS

Arterial pressure gradients dropped from 33 mm Hg (range 20-80 mm Hg) to 5 mm Hg (range 0-10 mm Hg) and pressure gradients in TCPC or caval veins dropped from 4 mm Hg (range 4-20 mm Hg) to 0 mm Hg (range 0-3 mm Hg). All stents were placed in the target lesion without complications. Three stent fractures without clinical instability were noted.

CONCLUSIONS

The CP stent is suitable for the treatment of vessel stenosis in congenital heart diseases from childhood to adulthood. Whether these good results will be stable in the long term needs to be investigated.

Breakable stent for interventions in infants and neonates: an animal study and histopathological findings

OBJECTIVE

To test in a neonatal animal model the feasibility and biocompatibility of a new breakable stent that can be broken open by balloon dilatation during reintervention for use in neonates and infants.

MATERIALS AND METHODS

Medical grade stainless steel breakable stents (n = 16) were interventionally implanted in systemic arteries in neonatal piglets (n = 7). Patency of the stented segments was shown by repeated angiography. Stents were redilated up to three times. After a follow up of 18-165 days the animals were killed and the tissue block containing the stent was excised. Besides standard histological examination, scanning electron microscopy was used for biocompatibility screening.

RESULTS

The stents were broken by redilatation with a conventional angioplasty balloon catheter. During follow up, patency of all stented segments was shown angiographically. One stent became dislocated during implantation. One vessel ruptured during redilatation when an inadequately large balloon catheter was used for dilatation. No other complications were observed. Scanning electron microscopy showed complete cellular coverage of the stent struts. Histological examination showed thinning of the vessel wall and partial rupture of the media at the site of stent breakage. An only mild inflammatory reaction was detected.

CONCLUSION

The new breakable stent can be broken open by simple angioplasty. Feasibility, effectiveness, and biocompatibility were shown in an animal model. Surgery to remove stents from paediatric patients due to disproportion between a previously implanted stent and the growing vessel may be avoided by the use of a breakable stent.

First successful implantation of a biodegradable metal stent into the left pulmonary artery of a preterm baby

Stent implantation in the youngest patients with a congenital heart disease implicates limitations concerning further vessel growth, the need of staged redilation, and later surgical removal. The search to overcome these restrictions led to open stent designs, with a wide adaptability to the vessel growth and recently to the development of bioabsorbable stent materials. A preterm baby born at 26 weeks of gestation was referred to our clinic following inadvertent ligation of the left pulmonary artery. Despite efficient debanding, the left lung perfusion was absent. Implantation of a biodegradable 3 mm magnesium stent was performed in a hybrid procedure when the baby weighed 1.7 kg. Reperfusion of the left lung was established and persisted throughout the 4-month follow-up period during which the gradual degradation process of the stent completed. Additional interventions, should they become necessary, seem not to be limited. Despite the small size of the baby, the degradation process was clinically well tolerated. The mechanical and degradation characteristics of the magnesium stent proved to be adequate to secure reperfusion of the previously occluded left pulmonary artery. Bioabsorbable stents with different diameters may help develop new strategies in the therapy of vessel stenosis in pediatric patients.

Stent implantation in the ductus arteriosus for pulmonary blood supply in congenital heart disease

Indications for catheter-based interventions in patent ductus arteriosus (PDA)-dependent pulmonary blood flow have yet to be defined. The aim of this study was to assess the acute and midterm outcome after stent implantation in the PDA. Between 1996 and 2002, ductal stenting was performed in 21 neonates and infants (14 females/7 males) to maintain pulmonary blood supply in cyanotic congenital heart disease (CHD). Balloon-expandable stents were implanted in the PDA with a final diameter of 4-5 mm without procedural deaths. Stent patency was achieved for 8-1,130 days (median, 142). Reintervention was necessary in nine patients. Overall survival rate after 6 years was 86%. Two neonates died a few days after the procedure due to right heart failure not related to PDA stenting. Corrective surgery was possible in six patients. An additional aortopulmonary shunt was needed in three patients; Fontan type operations were performed in six. One patient died after bidirectional Glenn shunt, another five reached palliation by additional perforation of the atretic valve/balloon valvuloplasty, and two are awaiting surgery. We conclude that in many patients with cyanotic CHD, especially in those with ductal pulmonary perfusion and additional forward flow from the right ventricle, ductal stenting is an effective transcatheter approach. Morphology of the PDA predicts the risk of restenosis and necessity of reintervention. Growth of the pulmonary vascular bed allows corrective or palliative surgery, and some patients can be cured by the intervention alone.