An Interesting Case and Literature Review of a Coronary Stent Fracture in a Current Generation Platinum Chromium Everolimus-Eluting Stent

Coronary interventions are the mainstay of treatment for stenotic coronary vascular lesions. New stent designs are constantly being evaluated to improve stent performances and clinical outcomes. Coronary stent fracture is uncommon; however, it is associated with potential major consequences including acute coronary syndrome and the need for repeated target vessel revascularization due to in-stent restenosis or stent thrombosis. We report a case of a 66-year-old man with an extensive cardiac disease history, who presented with intractable angina and was found to have a fracture of a current generation, platinum chromium everolimus-eluting stent (Synergy, Boston Scientific Inc.).

Coronary Stent Failure: Fracture, Compression, Recoil, and Prolapse

Current-generation coronary drug-eluting stents are associated with low rates of restenosis and target lesion revascularization. However, several mechanisms of stent failure remain clinically important. Stent fracture may occur in areas of excessive torsion or angulation. Longitudinal stent deformation is related to axial stent compression owing to extrinsic forces or secondary devices that disrupt stent architecture. Stent recoil occurs when a stent does not deploy at its optimal cross-sectional area. Tissue prolapse between stent struts may also predispose patients to adverse outcomes. Prevention, recognition, and treatment of these stent failures are necessary to optimize patient outcomes after percutaneous coronary interventions.

Two cases of immediate stent fracture after zotarolimus-eluting stent implantation

Drug-eluting stent (DES) implantation is currently the standard treatment for various types of coronary artery disease. However, previous reports indicate that stent fractures, which usually occur after a period of time from the initial DES implantation, have increased during the DES era; stent fractures can contribute to unfavorable events such as in-stent restenosis and stent thrombosis. In our present report, we describe two cases of zotarolimus-eluting stent fracture: one that was detected six hours after implementation, and the other case that was detected immediately after deployment. Both anatomical and technical risk factors contributed to these unusual cases of immediate stent fracture.

Microwave spectrometry for the evaluation of the structural integrity of metallic stents

PURPOSE

To assess the feasibility of a method based on microwave spectrometry to detect structural distortions of metallic stents in open air conditions and envisage the prospects of this approach toward possible medical applicability for the evaluation of implanted stents.

METHODS

Microwave absorbance spectra between 2.0 and 18.0 GHz were acquired in open air for the characterization of a set of commercial stents using a specifically design setup. Rotating each sample over 360°, 2D absorbance diagrams were generated as a function of frequency and rotation angle. To check our approach for detecting changes in stent length (fracture) and diameter (recoil), two specific tests were performed in open air. Finally, with a few adjustments, this same system provides 2D absorbance diagrams of stents immersed in a water-based phantom, this time over a bandwidth ranging from 0.2 to 1.8 GHz.

RESULTS

The authors show that metallic stents exhibit characteristic resonant frequencies in their microwave absorbance spectra in open air which depend on their length and, as a result, may reflect the occurrence of structural distortions. These resonances can be understood considering that such devices behave like dipole antennas in terms of microwave scattering. From fracture tests, the authors infer that microwave spectrometry provides signs of presence of Type I to Type IV stent fractures and allows in particular a quantitative evaluation of Type III and Type IV fractures. Recoil tests show that microwave spectrometry seems able to provide some quantitative assessment of diametrical shrinkage, but only if it involves longitudinal shortening. Finally, the authors observe that the resonant frequencies of stents placed inside the phantom shift down with respect to the corresponding open air frequencies, as it should be expected considering the increase of dielectric permittivity from air to water.

CONCLUSIONS

The evaluation of stent resonant frequencies provided by microwave spectrometry allows detection and some quantitative assessment of stent fracture and recoil in open air conditions. Resonances of stents immersed in water can be also detected and their characteristic frequencies are in good agreement with theoretical estimates. Although these are promising results, further verification in a more relevant phantom is required in order to foresee the real potential of this approach.