Small and preterm infants: The shrinking frontier of transcatheter patent ductus arteriosus closure

In the history of pediatric cardiovascular interventions, patent ductus arteriosus (PDA) closure has been momentous. It was Gross’s insubordination in 1938, closing a PDA surgically in a 7-year-old girl while his boss was away, that inaugurated pediatric cardiovascular surgery [1,2]. Almost three decades later, the frontier of pediatric interventional cardiology was crossed when Porstmann closed a PDA in a 17-year-old boy by deploying a polyvinyl alcohol foam plug through an 18-Fr femoral arterial sheath [3]. Now, 50 years and countless innovations after Porstmann’s pioneering work, transcatheter PDA closure remains at the frontier of our field, as illustrated by the concentration of studies related to this topic in the current [4–7] and recent [8–14] issues of Catheterization and Cardiovascular Interventions, as well as elsewhere [15,16]. In this issue, there are four articles focused on transcatheter PDA closure with recently approved, unapproved but dedicated, or off-label devices, which shine a spotlight on one of the most promising and challenging frontiers in congenital interventional cardiology, percutaneous anatomical intervention in small and preterm infants [4–7]. Wang-Giuffre and Breinholt [4] and Sathanandam et al. [5] describe their singleand multi-center experiences with PDA closure in small and preterm infants using the Medtronic Micro Vascular Plug (MVP), complementing a report by Boudjemline published earlier this year [14]. The MVP is a self-expanding PTFE-covered nitinol occlusion device that is approved “to obstruct or reduce the rate of blood flow in the peripheral vasculature,” which can be delivered through a microcatheter or diagnostic catheter with a lumen size as small as 0.02100 or 0.02700, depending on the device size. The authors of these reports describe promising technical outcomes with both arterial and venous delivery in preterm infants as small as 700 g, either through 3-Fr or 4Fr catheters or directly through a microcatheter without an arterial sheath. There were few device-related major adverse events, the device was able to be retrieved or manipulated after deployment, and delivery was supported with a combination of echocardiographic and fluoroscopic/angiographic guidance, which allows for limited contrast load. Based on these preliminary reports, the MVP offers promise in this application. Another article in this issue describes a relatively large single-center experience with PDA closure using the Amplatzer Duct Occluder II Additional Sizes device (ADOII-AS) [6], which was developed with an eye toward PDA occlusion in neonates and small infants [11]. Although only a handful of patients in the Mahmoud series could be considered “small,” and none were <3 kg, prior studies with this device have demonstrated successful PDA closure in a number of preterm infants under 2 kg using the ADOII-AS [8,10,15]. Similar to prior clinical reports on which it expands [8,10,15], the article by Mahmoud et al. reports a European experience, which speaks to the challenges around regulatory approval of implantable devices in the US. A US trial of the ADOII-AS was announced in October 2016, with an emphasis on small patients, but it has yet to begin enrolling. Notably, the