Coronary stent fracture in a saphenous vein graft to right coronary artery--successful treatment by the novel use of the Jomed coronary stent graft: case report and review of the literature

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.

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.

[Sirolimus-eluting stent displaced fracture: case report and review of the literature]

Drug-eluting stents have greatly reduced the risk of in-stent restenosis compared to bare metal stents by inhibiting neointimal growth. However, they may carry some long-term risks, especially the risk of late stent thrombosis. Recently, several cases of drug-eluting stent fracture have been also reported. The mechanisms, the diagnosis, the clinical implications and the management of this new complication are not well-known. We report the observation of a new case of displaced, sirolimus drug-eluting stent fracture. To our knowledge, this is the first reported case in France.

Coronary Stent Fracture

Coronary stent fracture is a relatively uncommon and rare complication of stent implantation. The reported incidence of stent fracture among drug-eluting stents ranges from 1% to 8%. Since 2003, when the use of drug-eluding stents was approved by the FDA for the treatment of coronary atherosclerosis, a number of retrospective and prospective studies and case reports have been published. We reviewed these publications to determine the incidence, predictors, clinical implications, and different management strategies for drug-eluding stent fracture in the coronary arteries. A review of the literature showed that the risk for stent fracture was higher with right coronary artery location, increased vessel tortuosity and angulation prior to stenting, use of overlapping stents, and use of longer stents. A higher risk of bare metal stent fracture was reported in saphenous vein bypass grafts. The authors also report in this issue in the Department “Case Study” a symptomatic fracture of a sirolimus-eluding Cypher® stent in the mid-left anterior descending artery.

Drug-eluting stent fracture: incidence, contributing factors, and clinical implications

Stent fracture has been observed in noncoronary vessels, especially in the superficial femoral and popliteal arteries and with bare metal stents in saphenous vein grafts of coronary arteries. Since the introduction of drug-eluting stents, stent fractures have also been reported in small studies and case reports. We reviewed these publications to assess what is known regarding the incidence, contributing factors, and clinical implications of drug-eluting stent fracture in coronary arteries. The reported rate of drug-eluting stent fracture in coronary arteries ranges from 1 to 8%, although much of the available literature is derived from single-center studies that are heterogeneous in their study methods. A higher risk of stent fracture may be associated with the right coronary artery location, excessive tortuosity or angulation of the vessel, overlapping stents, and longer stents. The closed-cell design of the Cypher stent has been associated with increased rigidity that may increase the risk of stent fracture, although these studies did not assess the overall outcomes between the Cypher and Taxus stents in a head-to-head comparison. Stent fracture has been shown by most studies to be associated with a statistically increased incidence of focal in-stent restenosis, and some have shown an increased risk of target lesion revascularization. Other complications observed with stent fracture include stent thrombosis, coronary aneurysms, myocardial infarction, and sudden death.

Clinical relevance and treatment of carotid stent fractures

OBJECTIVE

To review all published reports and investigate the clinical relevance and need for treatment of carotid stent fractures.

METHODS

Electronic and hand-searching of the published literature and the Manufacturer and User Facility Device Experience (MAUDE) database.

RESULTS

Thirteen articles were published. There are 10 case reports and 3 clinical studies. There are 26 reports of fractured stents in the MAUDE database. Fifty-five cases of carotid stent fractures are reported in total. A total of 201 carotid stents were examined in the 3 studies, and the incidence of fractures was 8.9% (18/201). Fractured stents were 22 Xact, 20 Acculink, 6 Precise, 2 Exponent, 1 Nexstent, 1 Genesis, 1 Symbiot, and 2 nonspecified nitinol self-expandable stents. Twenty-seven of the treated carotid lesions were atherosclerotic, 3 restenoses after carotid endarterectomy, 2 postradiational, 1 pseudoaneurysm, and 22 lesions of unknown pathology. Calcification was reported in 15 of the 27 atherosclerotic lesions (55.5%). Time from implantation to fracture ranged from 0 days (fracture during implantation) to 37 months. In 55% of the cases, stent fracture was associated with restenosis. Six patients presented with symptoms. Treatment was reported for 32 patients: 14 patients underwent de novo stent placement, 2 balloon angioplasty, 2 carotid endarterectomy, 2 bypass graft (1 vein, 1 polytetrafluoroethylene), 1 anticoagulation, and 11 patients were followed up.

CONCLUSION

Carotid stent fractures are mainly reported in self-expandable nitinol stents. Plaque calcification may be a risk factor for stent fractures. No difference was observed between open and closed-cell design. Stent fractures were often associated with restenosis and usually were asymptomatic. The actual incidence, clinical relevance, and optimal treatment remain to be clarified from larger prospective studies designed to investigate the issue.

Complete fracture of sirolimus-eluting stent in a saphenous vein graft to left anterior descending artery

Coronary stent fractures have been suggested as a potential new mechanism of restenosis. The mechanical properties of stents were designed not only to prevent vessel recoil, but also to resist the mechanical stress of vessel movement over millions of cardiac cycles. We present a case in which mechanical stress may have contributed to the fracture of a stent implanted in a saphenous vein graft (SVG) to the left coronary artery. The patient was admitted due to chest pain 2 years after receiving a coronary artery bypass graft. A coronary angiography revealed the culprit vessel to be the SVG to the left coronary artery. The graft was stenosed and was stented with a sirolimus-eluting stent. A 6-month follow-up coronary angiography revealed 80% in-stent restenosis with stent fracture. We re-intervened by balloon angioplasty. This is the first report of sirolimus-eluting stent fracture combined with restenosis of SVG in Korea.

Drug-eluting stent fracture and acute coronary syndrome

BACKGROUND

Coronary stent fracture is an underrecognized entity but has been reported more frequently in the drug-eluting stent (DES) era. Nevertheless, the clinical implications of coronary stent fracture remain unclear.

METHODS AND MATERIALS

A literature search for reports of DES fracture was conducted via MEDLINE, and the US Food and Drug Administration Manufacturer and User facility Device Experience (MAUDE) database was accessed via the internet and interrogated for reports of stent fracture between January 1, 2003, and April 30, 2008. Each report was reviewed, and clinical information was extracted for analysis.

RESULTS

The MEDLINE search identified 202 cases of coronary DES fracture, with 95% of cases involving Cypher sirolimus-eluting stents. Clinical information regarding patient presentation was available in 96 cases. Patients presented with ST-elevation myocardial infarction (STEMI) or stent thrombosis in six cases (6%) and with unstable angina or non-STEMI (NSTEMI) in 40 cases (42%). The MAUDE database search identified 337 stent fracture reports, with 97% of cases involving Cypher stents. Clinical information regarding patient presentation was available 193 cases. Patients presented with STEMI or stent thrombosis in 24 cases (12%) and with unstable angina or NSTEMI in 36 cases (19%).

CONCLUSIONS

Most reports of drug-eluting stent fracture involve Cypher stents. DES fracture can be associated with stent thrombosis, myocardial infarction and angina. However, whether the incidence of such events reported in the literature and in the MAUDE database is representative of all patients experiencing stent fracture remains unclear.

Intravascular foreign bodies: danger of unretrieved fragmented medical devices

A warning on the danger of unretrieved device fragments and recommendations to mitigate the danger were issued by the Food and Drug Administration in January 2008. The causes of intravascular foreign bodies are classified into three main categories: improper manipulation and usage, device defects, and others, such as patient and anatomical factors. Device failure after long-term use is rarely predicted at the time of approval, since device abnormality is rarely experienced in animal studies and clinical trials conducted during development of the device. Stent fracture due to metal fatigue is one example. Complex complications could occur from simultaneous use of two or more devices with diverse characteristics. The success rate of percutaneous retrieval of intravascular foreign bodies has improved with the advances in commercially available devices. However, the procedure is not always successful and sometimes surgical removal becomes necessary. Appropriate device selection and acquisition of experience in using the device are important. When an intravascular foreign body cannot be retrieved, the risk of complication could be high. Magnetic resonance imaging examination sometimes causes adverse events, including burns due to the heat generated by metal movement. Such information should be correctly recorded. Furthermore, it is necessary to provide patients with adequate information about the characteristics of implanted devices and unretrieved fragments. We reviewed the literature on unretrieved medical device fragments and include articles that describe the Japanese experience.

Acute coronary syndrome due to complete bare metal stent fracture in the right coronary artery

Stent fracture (SF) was suggested to be an unusual cause of restenosis after drug eluting-stent implantation. However, angiographically visible complete SF after bare metal stent (BMS) implantation is extremely rare. Here we report a case of SF of a BMS representing with acute coronary syndrome (ACS). To our knowledge, this is the first report of early fracture of a BMS in the right coronary artery, resulting in ACS.

In situ fracture of stents implanted for relief of pulmonary arterial stenosis in patients with congenitally malformed hearts

BACKGROUND

One of the most common uses of stents in patients with congenitally malformed hearts is treatment of pulmonary arterial stenosis. Although there are reports of fractured pulmonary arterial stents, little is known about the risk factors for, and implications of, such fractures.

METHODS

We reviewed angiograms to identify fractures in stents previously inserted to relieve stenoses in pulmonary arteries from 1990 through 2001 in patients who also underwent follow-up catheterization at least 3 years after placement of the stent. We undertook matched cohort analysis, matching a ratio of 2 fractured to 1 unfractured stent.

RESULTS

Overall, 166 stents meeting the criterions of our study had been placed in 120 patients. We identified fractures in 35 stents (21%) in 29 patients. All fractured stents were in the central pulmonary arteries, 24 (69%) in the central part of the right pulmonary artery, and all were complete axial fractures, or complex fractures along at least 2 planes. Stent-related factors associated with increased risk of fracture identified by multivariable logistic regression included placement in close apposition to the ascending aorta (p = 0.001), and a larger expanded diameter (p = 0.002). There was obstruction across 28 of 35 fractured stents, which was severe in 11. We re-stented 21 of the fractured stents, and recurrent fracture was later diagnosed in 3 of these. A fragment of the fractured stent embolized distally in 2 patients, without clinically important effects.

CONCLUSIONS

In situ fracture of pulmonary arterial stents is relatively common, and in most cases is related to compression by the aorta. There is usually recurrent obstruction across the fractured stent, but fractured stents rarely embolize, and are not associated with other significant complications.