Absorbable metal stents for vascular use in pediatric cardiology: progress and outlook

Abstract

The past five years have yielded impressive advancements in fully absorbable metal stent technology. The desired ultimate ability for such devices to treat a vascular stenosis without long-term device-related complications or impeding future treatment continues to evoke excitement in clinicians and engineers alike. Nowhere is the need for fully absorbable metal stents greater than in patients experiencing vascular anomalies associated with congenital heart disease (CHD). Perhaps not surprisingly, commercially available absorbable metal stents have been implanted in pediatric cardiology patients with conditions ranging from pulmonary artery and vein stenosis to coarctation of the aorta and conduit/shunt reconstructions. Despite frequent short term procedural success, device performance has missed the mark with the commercially available devices not achieving degradation benchmarks for given applications. In this review we first provide a general overview detailing the theory of absorbable metal stents, and then review recent clinical use in CHD patients since the release of current-generation absorbable metal stents around 2019. We also discuss the challenges and our center's experience associated with the use of absorbable metal stents in this pediatric population. Lastly, we present potential directions for future engineering endeavors to mitigate existing challenges.

Keywords: absorbable metals; iron; magnesium; pediatric stents; zinc.

Figure 1

Schematic denoting the tiers that determine the corrosion rate for absorbable metal materials as discussed in the associated text. Created with BioRender.com.

Figure 2

Absorbable metal stents discussed in the current review. Adapted and used with permission where applicable (, –78).

Figure 3

Figure adapted with permission from reference (73). (A–C) Show micro CT scans from stent materials explanted from three patients at 6 months (A) and 16 months (A,C). At 6 months, macrophages with hemosiderin in the cells are seen near the strut (D) At 16 months, the authors report the tissue repair was resolved without necrocytosis (E,F). (G) Shows embolized stent fragments to the right pulmonary artery (broken arrow) compared to the original implanted stent (solid arrow). (H) Right ventricular angiogram showing that flow is not compromised where the stent material was embolized. (I) Shows that the right atrium is not enlarged and there is no more septal bulge toward the left atrium, post right ventricle overhaul and right ventricular outflow tract reconstruction.

Figure 4

Adapted with permission from reference (75). Restenosis of the Magmaris scaffold 21 days after prior implantation for native coarctation of the aorta (A), and after balloon dilatation (B) Maverick 4.0 × 20 mm, 8 bar and Maverick 4.5 × 20 mm 6 bar). Re-intervention led to a reduction in the blood pressure gradient from 48 to 18 mmHg with a minimal diameter of 3.2 mm.

Figure 5

Images from a complex case undergoing implantation of multiple IBS Angel stents at our center (case 1). (A) Posterior view of 3D CT 7 weeks post stenting showing PDA stent, banded branch pulmonary arteries and IBS Angle stents (arrows) in the proximal right (RPV) and left pulmonary veins (LPV). (B) RPV 7 weeks post hybrid IBS Angel implantation, (C) RPV recurrent stenosis at 2 months (arrow), (D) RPV following implantation of a second stent at 2 months, and (E) RPV angiogram after serial reinterventions. (F) Axial CT of LPV 7 weeks post hybrid IBS Angel implantation, (G) LPV recurrent stenosis at 2 months (arrow), (H) LPV implantation of a second stent at 2 months, (I) LPV angiogram after serial reinterventions.

Figure 6

Images from another use of absorbable metal stents at our center (case 2). (A) 3D rotational angiogram of RV outflow tract prior to intervention, (B) lateral angiogram following direct injection in RVOT prior to stenting, and (C) lateral angiogram post implantation of 2 IBS Angel stents.