Morphologic characterization of the patent ductus arteriosus in the premature infant and the choice of transcatheter occlusion device.

OBJECTIVES: The aim of this study was to describe and differentiate the morphology of patent ductus arteriosus (PDA) seen in children born prematurely from other PDA types. BACKGROUND: PDAs are currently classified as types A-E using the Krichenko's classification. Children born prematurely with a PDA morphology that did not fit this classification were described as Type F PDA. METHODS: A review of 100 consecutive children who underwent transcatheter device closure of PDA was performed. The diameter and length (L) of the PDA and the device diameter (D) were indexed to the descending aorta (DA) diameter. RESULTS: Comparison of 26 Type F PDAs was performed against, 29 Type A, 7 Type C and 32 Type E PDAs. Children with Type F PDAs (median 27.5 weeks gestation) were younger during the device occlusion compared with types A, C, and E (median age: 6 vs. 32, 11, and 42 months; P = 0.002). Type F PDAs were longer and larger, requiring a relatively large device for occlusion than types A, C, and E (Mean L/DA: 1.88 vs. 0.9, 1.21, and 0.89, P ≤ 0.01 and Mean D/DA: 1.04 vs. 0.46, 0.87, and 0.34, P ≤0.01). The Amplatzer vascular plug-II (AVP-II) was preferred for occlusion of Type F PDAs (85%; P <0.001). CONCLUSIONS: Children born prematurely have relatively larger and longer PDAs. These "fetal type PDAs" are best classified separately. We propose to classify them as Type F PDAs to add to types A-E currently in use. The AVP-II was effective in occluding Type F PDAs.

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.