First ad hoc bioresorbable vascular scaffold bench test: A glimpse into percutaneous bifurcation interventions

Abstract

The advent of a fully bioresorbable stent has been advocated as a breakthrough in interventional cardiology [1]. After transiently assuring radial strength, this device is fully resorbed, leading to restoration of the vessel's biological properties. However, although representing a truly innovative technology, the evolutionary impact of the bioresorbable vascular scaffold (BVS) appears somewhat shadowed by its intrinsic polymeric nature, which is not designed to tolerate the mechanical stresses that metallic stents typically endure during percutaneous bifurcation interventions. Indeed the Instruction For Use (IFU) of ABSORB (Abbott Vascular, Santa Clara, CA), the only commercially availableBVS, state to “avoid scaffolding across any sidebranch≥2 mmin diameter” because “balloon dilation of any cells of a deployed BVS will cause scaffold damage”. Nevertheless, the availability of the BVS in an increasing number of catheterization laboratories has entailed a more liberal use of the device engendering the feeling that manufacturer's recommendations are excessively restrictive. Coupled to the rush for originality typically accompanying new technology, the lack of knowledge on the actual deformation capability of the BVS might be clinical harmful. Surprisingly, no bench test has been performed to date, possibly due to the high cost of the device and/or reluctance of the manufacturer to provide samples for such kind of investigation. We therefore take the opportunity of a non-implanted BVS to gain some insight into the structural features of this device, with special focus on its possible role in percutaneous bifurcation interventions. Because the IFU advised against reintroducing an ABSORB that has been retracted into the guiding catheter owing to the start of the polymer degradation process, we implemented a very simple bench test immediately after the end of the percutaneous coronary intervention, recycling the materials that have been used for the procedure. The test has been conducted in a liquid bath at body temperature (37 °C) to simulate the conditions in which the BVS inherent expansion occurs (Fig. 1A). All inflations were performed according to IFU, i.e. 2 atm increments every 5 s up to nominal pressure. After inflation of its delivery balloon, the expanded scaffold was placed over a stylet helping its manipulationwithout the need for touching. A cell was then crossed by a coronary guide wire and by a 2.5 mm diameter balloon (Fig. 1B) that was inflated. The BVS was then rapidly imaged. The scaffold showed mild dilation of the cell toward its external side with no apparent breaking of the structure (Fig. 2A and B). The same cell was further expanded with a 3.0 mm balloon inflation. Results showed a more significant modification of scaffold structure better revealing themechanism of cell dilation, i.e. up and down displacements of the ring arc delimiting the cell determining a small reduction of the scaffold internal caliber (Fig. 3A and B). To further assess the potential role of ABSORB in the treatment of bifurcation lesions, we over-expanded the segment starting from the dilated cell with a 3.5 mm and a 4.0 mm non-compliant balloon (respectively 0.5 mm and 1.0 mm larger than the nominal diameter of