Transcatheter closure of patent ductus arteriosus has an established safety and efficacy in childhood using coils. However, complications and unexpected events are infrequently reported, such as haemolysis, embolisation, and stenosis of the left pulmonary artery or descending aorta. In the current work, we report an unusual obstacle that occurred upon the release of a patent ductus arteriosus coil in a child. Abnormal straightening of the coils on the pulmonary side was encountered, with failure of recoil of the patent ductus arteriosus windings noticed upon the coil release. However, the coil was successfully snared, and another was deployed with an uneventful recovery.

The straightening–unstraightening correspondence of Grothendieck–Lurie provides an equivalence between cocartesian fibrations between $(\infty, 1)$-categories and diagrams of $(\infty, 1)$-categories. We provide an alternative proof of this correspondence, as well as an extension of straightening–unstraightening to all higher categorical dimensions. This is based on an explicit combinatorial result relating two types of fibrations between double categories, which can be applied inductively to construct the straightening of a cocartesian fibration between higher categories.