Article Text

  1. M. I. Vidovich1,
  2. D. C. Lee1,
  3. E. Wu1,
  4. B. D. Myers1,
  5. V. P. Dravid1,
  6. C. J. Davidson1
  1. 1Division of Cardiology, Feinberg School of Medicine, Chicago


Background Cardiac magnetic resonance (MR) of bare-metal stents appears to be free of any potential adverse clinical effects. However, the effect of MR scanning on polymer coating of drug-eluting stents might potentially cause disruption or peeling of polymer and potentially affect anti-restenosis benefits. We performed an in vitro study of drug-eluting stents to determine stability of polymer coating under simulated cardiac MR scanning conditions and to determine effects of balloon expansion on polymer integrity.

Methods Six Cypher (Cordis, Miami, FL) and three Taxus (Boston Scientific, Natick, MA) stents were studied. The stents were imaged with an environmental scanning electron microscope (ESEM) before and after balloon expansion to nominal stent inner diameter. Expanded stents along with weight ballast were then placed in the center of a clinical 1.5 T MR scanner (Sonata, Siemens). Imaging protocols were performed to simulate a complete clinical cardiac examination (multiple cines were obtained using a steady-state free precession and viability images with an inversion-recovery gradient echo). Stents were observed with ESEM after 1 simulated cardiac MR scan and again after 5 repeated MR scans. The stents were observed in an FEI Quanta 600F ESEM (FEI Company, Hillsboro, OR) equipped with field emission electron gun and Oxford energy dispersive x-ray spectrometer. The ESEM was operated at 15 kV and chamber pressure of 1.5 Torr, which allowed direct observation and elemental analysis without a conductive coating.

Results The polymer coating was intact in both stent types prior to balloon expansion. After balloon inflation, Cypher stent showed multiple microfractures (< 2 μm) while Taxus stents showed frequent adhesion of polymer to adjacent struts (Figure). One Taxus stent revealed significant (200 μm) peeling of polymer from the stent surface after balloon expansion. There were no significant additional deformities or surface irregularities observed on either of the stent models after one and five simulated MR scans.

Conclusions There are no observable deformities of the polymer induced by MR scanning of the two commercially available drug-eluting stents in this in vitro experiment. Clinical implications of adhesions and peeling following balloon expansion of Taxus stent and microfractures on Cypher stent are unknown.

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