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Multiple Stent Fractures at the Site of Coronary Artery Bypass Insertion

Introduction

The development of drug-eluting stents (DES) has led to a significant reduction of restenosis by effectively suppressing neointimal growth when compared to bare metal stents. Nevertheless, in-stent restenosis after DES implantation still occurs [1]. Several mechanisms of in-stent restenosis were discussed, including stent underexpansion, polymer disruption, and drug restistance [2]. Recently, several cases of restenosis in DES in association with stent fracture (SF) were reported. Almost all SF were found to occur in sirolimus eluting stents (SES) [3,4]. SF was found to be present in 44% of focal or totally occluded stents, suggesting that SF is a relevant cause of focal in-stent restenosis in DES [2]. We report the unusual case of a patient with multiple SF at the site of coronary artery bypass insertion.

Case Report

A 57-year-old male patient with a history of posterolateral myocardial infarction due to occlusion of the left circumflex artery and fibrinolysis in 1991 presented to a remote hospital with worsening chest pain. He was found to have a 75–90% stenosis in the mid portion of the left anterior descending artery (LAD) and no angiographically relevant stenosis in the left circumflex (LCx) or right coronary artery (RCA) was present. He was treated with coronary artery bypass graft surgery using the left internal mammarian artery as conduct to the mid portion of the LAD. In 1997, he experienced worsening chest pain on exertion and was found to have progression of the stenosis proximal to the insertion of the bypass. Since the blood flow via the bypass was believed to be not sufficient by angiography, a PCI of this stenosis with additional placement of a bare metal stent (2.5/33 mm) was performed. Eight years later (2005) the patient complained of exertional dyspnea and chest discomfort resembling his previous episodes of angina. Angiography showed functional occlusion of the bypass with retrograde filling from the LAD and 75% stenosis of the native LAD at the site of the bypass insertion. Two SES, 3.5/ 33 mm proximaly and 2.5/18 mm distally, were implanted. Fluoroscopy revealed 5 mm overlapping of the two stents (Fig. 1A) and an excellent angiographic result (Fig. 1B) without any residual stenosis. In 2006, the patient presented again with worsening symptoms. Angiography revealed high-grade angulation of the stented segment in the area of the bypass insertion and a 90% stenosis which was thought to be caused by a gap between the two previously implanted SES (Fig. 2A–C). The lesion was treated with a third SES (3.5/33 mm) overlapping the other two stents (Fig. 2D). Poststenting angiogram showed a good result. Furthermore, the patient had a 75% stenosis of the RCA which was treated with another SES (3.0/33 mm). A month later, the patient returned to the remote hospital with the same symptoms. This time he was found to have a 75% stenosis at the site of bypass insertion which was again thought to be a gap between the previously implanted stents. The fractional flow reserve (FFR) was measured to evaluate the functional significance of the stenosis and was found to be borderline (0.81). Driven by the FFR measurement and the complaints of the patient, again a SES was placed (3.5/8 mm) at the site of bypass insertion. After 1 month the patient’s symptoms returned again. The patient was presented at our institution and an angiography was performed. A 90% stenosis was found at the site of the bypass insertion and a gap was noted between the implanted stents. Unaware of the complete history of the patient, this was thought to be caused by inaccurate previous stent placement and the decision was taken to perform again a stent placement at this site (SES 3.5/13 mm). Poststenting angiography revealed again an excellent result. Ten months later the patient presented again to this institution with chest pain and dyspnea during exertion similar to the previous episodes. A review of the patient’s previous angiograms showed overlapping of all previously placed stents at the time of implantation and a gap between the stents at the site of the insertion of the bypass at the following examinations indicating multiple SFs. Fluoroscopy showed a 50% stenosis at the site of bypass insertion and again a gap between the stent fragments indicating a fourth SF (Fig. 3). It also showed increased movement and angulation of the LAD at this site during the cardiac contraction due to the bypass serving as a hinge point. FFR was found to be 0.91 indicating that the stenosis was not hemodynamically relevant at this time. Therefore, a further intervention was not indicated. The patient was closely monitored on an outpatient basis and the patient was advised to undergo surgical removal of the bypass graft, before a further intervention was justified.

Fig. 1.
Fluoroscopy of the LAD after implantation of two SES. The image shows the overlapping of the two SES 2.5/18 mm (a) and 3.5/33 mm (b) and the previously implanted BMS 2.5/33 mm (c) right after implantation (A) and an excellent morphologic result after revascularization (B). It also shows the angulation of the stented segment at the site of coronary artery bypass insertion (arrow).

Fig. 2.
Fluoroscopy two years after the implantation of two SES in the LAD. At the site of the bypass insertion a 75 % stenosis is visible (A). During the cardiac cycle the stented segment is exposed to high-grade angulation and a gap between two stented segments is visible (arrows) (B, C). A third SES 3,5/33 mm (a) was implanted at the site of the gap (D).

Fig. 3.
Fluoroscopic image ten months after the implantation of the fifth DES in the LAD. The picture shows a stent fracture at exactly the same site as before.

Discussion

SFs are a known complication after vascular stent implantation. Extreme mechanical stress due to excessive angulation of the vessel is proposed to be the most likely cause for these fractures. They were reported to occur in highly mobile parts of the body like the subclavian, iliac, or femoral artery [5–7]. In the coronary arteries, they are a rare finding but appear to be an important cause for instent restenosis in DES [4]. Several factors may have contributed to the multiple SF in this patient. SF is more commonly observed in DES than in bare metal stents. Therefore, it was speculated that the coating during the production process may weaken the stent metal. Furthermore, the lack of neointimal formation could result in a reduced mechanical support of the stent by the surrounding tissue [2]. In this case, all fractured stents were SES. Most cases of SF in DES were reported in SES which have a closed cell design. Paclitaxel eluting stents have an open cell design resulting in lower shear forces which may lead to a lower incidence of SF [4]. In a study by Aoki et al. [8] all SF were found at hinge points of vessel movement during the cardiac cycle. It can be speculated that increased angulation of the stented LAD segment during contraction as a result of bypass insertion was the single most important factor of the SFs in this case. Furthermore, most of the implanted SES were long stents. Such stents are exposed to higher radial forces during the cardiac contraction cycle especially at the mid portion. The same applies for overlapping stents as in this case. In two papers, SF of the middle stent of three overlapping stents was reported. Metal deformation and subsequent SF was also reported to occur at the extremities of overlapping stents, at which each extremity may act as a fulcrum [9,10].

References

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Autor: Holger Hetterich, MD and Johannes Rieber, MD

Fuente: Catheterization and Cardiovascular Interventions 73:84–87 (2009)

Ultima actualizacion: 26 DE ENERO DE 2012

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