Unzipping of small diameter stents: an in vitro study.

OBJECTIVE: The purpose of this study was to determine if small-diameter stents can be unzipped in vitro. BACKGROUND: Small-diameter stents can relieve stenosis in infant blood vessels. As the child grows, refractory stenosis may result. If an implanted stent can be intentionally fractured along its length-"unzipped," it can be redilated to the eventual adult vessel diameter. METHODS: Stents of diameters ≤6 mm were dilated using angioplasty balloons until they fractured. The change in length-diameter (dL/dD ratio), and the yield-point-force (σy ) for each stent was calculated. RESULTS: Thirty-four coronary (CS), 11 biliary, and 10 nitinol peripheral stents (median diameter = 4, 5, and 6 mm; range = 2.75-4.5, 4-6, 6 mm, respectively) were tested. Stainless-steel (SS) CS unzipped predictably at twice their nominal diameter with minimal shortening (n = 24, median dL/dD = 0.4). Nitinol stents fractured in a disorganized fashion. The remaining stents unzipped, had disorganized fractures, and shortened significantly (dL/dD>1). A dL/dD ratio of<1 had a strong, positive correlation with the ability to unzip (Pearson rho = 0.94). By multivariate regression analysis, SS alloy, and closed-cell design were found to be significant predictors (P < 0.05) for unzipping. Optimal cut-off points for stents to unzip included, strut-thickness = 112 µm, alloy-density = 7.7 g/cm(3) , dL/dD ratio = 0.12 and σy = 108Mpa (Youden's index = 0.8, 0.4, 0.8, and 0.5, respectively). CONCLUSIONS: Stainless-steel, coronary stents of a closed-cell design unzip at twice their nominal diameter without significant shortening when serially dilated. This study may encourage the implantation of small stents in infant blood vessels and aid in selection of appropriate stent type.

New Patent Ductus Arteriosus Closure Devices and Techniques.

Patent ductus arteriosus (PDA) in extremely low-birth-weight infants puts this vulnerable population at high risks of morbidity and mortality. Inclusion of a multidisciplinary team and newly available transcatheter PDA occlusion devices in the management of these infants can mitigate those risks and promote better long-term outcomes. It is important that specific techniques with venous-only approach outlined in this article be followed to achieve optimal results.

Acute and long-term effects of endovascular debanding of pulmonary arteries in a swine model.

OBJECTIVES: The primary objective of this study was to demonstrate that pulmonary artery (PA) debanding via cardiac catheterization using balloon angioplasty is feasible and safe in swine. The secondary objectives were to determine the acute and long-term effects of this therapy. DESIGN: This is a chronic survival experimental study in newborn swine. BACKGROUND: PA bands are used in infants for transient palliation of congenital heart defects with excessive pulmonary blood flow. Although rare, if these defects should close spontaneously or become hemodynamically insignificant, a sternotomy and occasionally cardiopulmonary bypass may still be required for band removal. Alternatively, debanding could be accomplished through less invasive methods. INTERVENTIONS: The main pulmonary artery was banded in three piglets, and the left pulmonary artery in five piglets via mini-thoracotomy at a mean weight of 2.5 kg. Following a threefold increase in weight, the piglets underwent PA debanding via balloon angioplasty. Four piglets were sacrificed to evaluate the acute effects. The remainder were followed to evaluate long-term effects. Histopathology was performed on all piglets. OUTCOME MEASURES: Reintervention rates. Histopathologic consequences of high pressure balloon angioplasty used for PA debanding acutely and after reinterventions. RESULTS: Debanding was performed at a mean weight of 8.1 ± 2.23 kg. The median preintervention gradient across the band was 18 mm Hg. Debanding was successful in all piglets. The median postintervention gradient was 3.5 mm Hg. All piglets in the long-term model required re-interventions for recurrent stenosis at mean weights of 26 ± 1.6 and 61 ± 3.2 kg. Histopathology demonstrated vessel wall injury in only one piglet. CONCLUSIONS: Endovascular PA debanding can be safely achieved in a swine model. Angioplasty following debanding may be necessary for recurrent stenosis. This catheter-based therapy may provide a less-invasive alternative to surgery.