Andersons pediatric cardiology 1091

In view of the acknowledged morbidity associated with surgical ductal closure, there has been an increased interest in closing the patent arterial duct percutaneously in very small infants with weights as low as 750 g.193–199 The experience with this approach has been increasing over the past few years, with encouraging results from a diverse number of centers Closure can be achieved with coils,194 the Medtronic Vascular Plug,195 or one of the Amplatzer family of occluders.41,196–199 To reduce radiation exposure to these fragile newborns, transthoracic echocardiographic monitoring for the implantation limits or eliminates fluoroscopy, has proven effective, and allows the procedure to be performed in the neonatal unit.197,199 In the study by Zahn et al.,199 catheter closure was attempted in 24 extremely premature newborns at a mean age of 1 month and weight of 1249 g (range 755 to 2380 g) There were three procedural failures related to the development of left pulmonary artery stenosis due to the device (Amplatzer AVP II), and all devices were removed uneventfully The device resulted in left pulmonary artery stenosis in one infant, requiring a stent in follow-up There were no procedural deaths, postligation syndrome, residual ductal flow, or device embolization Twenty-three of 24 infants survived to discharge, with one late death unrelated to the procedure After a median followup period of 11 months, all infants were alive and well, with no residual ductal flow or evidence of pulmonary artery or aortic coarctation Nevertheless, overall mortality remains high but more often is related to continuing respiratory distress, intracranial hemorrhage, necrotizing enterocolitis, or coagulopathy, rather than the therapies themselves.177 Outcomes are also influenced by the duration of the waiting time for surgery/catheter intervention after failed medical management, perioperative care, and in some situations the need for potential transport to facilities with surgical/catheter capacity.200 Many questions remain unanswered concerning the true impact of a large left-to-right ductal shunt on the course and outcome of prematurity and respiratory distress syndrome.136,201 Indeed, over the past decade, neonatal intensive care units have seen a significant decrease in the diagnosis and treatment of the premature infant's arterial duct, with little evidence of an increase in morbidity.202 In a large multicenter trial, one-third of infants with a significant duct had spontaneous closure, and indomethacin-induced closure in 70% of infants treated There was no difference in the rate of closure if indomethacin was given immediately on diagnosis or after 48 hours of intensive medical therapy Rates of death were identical in patients treated with indomethacin early, with indomethacin given late, or with surgery, being approximately 13% overall in each group.203 Infiltration of Formalin, Balloon Dilation, Implantation of Stents, and Bioengineering of the Arterial Duct Rudolph and colleagues204 described a technique of subadventitial formalin infiltration of the wall of the duct designed to maintain long-term patency of the vessel in patients with duct-dependent cardiac malformations in whom surgery was either inadequate or not feasible However, it was shown that infiltration of formalin did not ensure ductal patency even for a short time.205 The technique was abandoned in favor of infusion of prostaglandin E1 Percutaneous balloon dilation has also been proposed as a method to maintain ductal patency.206 Temporary patency can be achieved, but abrupt closure, thrombosis, or rupture can occur, making this a less reliable means of assuring patency Except for special instances, this technique has not been pursued clinically To provide a mechanical scaffold for the ductal wall, resistant to the constrictive forces of ductal closure, Coe and Olley207 proposed the implantation of endovascular stents This approach, using either self- or balloon-expandable stents, has had expanding clinical application The implantation in anatomically uncomplicated ducts, such as in pulmonary atresia, critical pulmonary stenosis, or the hypoplastic left heart syndrome (Fig 41.19; video 41.2), has been encouraging.208–212 However, use in more complex situations, such as occurs in tetralogy with pulmonary atresia can be technically difficult.213 With innovative approaches to deliver the implant, such as cut-down of the carotid arteries, transvenous through a ventricular septal defect, or after radiofrequency-assisted balloon dilation of an atretic pulmonary valve, the procedure can be performed even in ducts that originate from the undersurface of the aorta or are tortuous (Videos 41.3 and 41.4) Largely, application has been advanced through improved design of the stents, such as flexible balloon platforms or systems with lower profiles, or taking advantage of the potential of drug-eluting implants to alter the vessel reactivity, thus reducing in-stent stenosis At the Hospital for Sick Children in Toronto, Lee and colleagues214 investigated the use of a rapamycin-coated stents implanted into the duct of small newborn pigs The mean luminal diameter of bare metal implants compared with the drug-eluting stents was smaller by 32% and 42% at 4 and 6 weeks, respectively, by inhibition of neointimal formation (Fig 41.20) In clinical application in infants,215 such ductal implants saw peak rapamycin levels 20 times higher and clearance 30 times lower than reported in older children and adults, within the immunosuppressive range for prolonged periods but with no observable clinically significant adverse outcomes Although the role of stents in the management of infants with complex ductal-dependent lesions has yet to be fully defined, such studies are very promising The arterial duct may also serve as a conduit to decompress the pulmonary circulation in the setting of idiopathic pulmonary hypertension Reopening and stenting the duct has proven efficacious in this clinical setting.216–218 FIG 41.19 Left, Infant with hypoplastic left heart syndrome awaiting cardiac transplantation The duct became stenotic and unresponsive to prostaglandin Pulmonary arterial angiogram depicts a stent placed transvenously across the duct to relieve the stenosis Right, Aortogram is seen after implantation of a stent in an infant with pulmonary atresia and intact septum who was prostaglandin dependent