Acute ST-Elevation Myocardial Infarction 6 Years Following a Sirolimus-Eluting Stent Secondary to Complete Stent Fracture

ABSTRACT: With increasing coronary interventions, coronary stent fracture following implantation of drug-eluting stents is being commonly recognized. Though isolated strut fractures are often only incidental findings, more severe forms of stent fracture with complete transection have adverse clinical outcomes. Most such cases are reported within several months following the index angioplasty. We report an unusual presentation of late stent fracture following a sirolimus-eluting stent, presenting with acute myocardial infarction 6 years after the initial stent implantation. The various mechanisms underlying fracture of drug-eluting stents are reviewed. Because no known mechanisms were noted in our case, unknown factors may also play a role in the genesis of stent fracture. Clinicians need to be aware that such complications may present rarely, extremely late after the index procedure as an acute myocardial infarction.

J INVASIVE CARDIOL 2012;24(4):E64-E66

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Though the use of drug-eluting stents (DES) has significantly reduced in-stent restenosis, complications like aneurysm formation, stent thrombosis, and stent fracture are also being reported with their use. The prevalence of stent fracture following DES ranges between 1% and 5%, with most cases present within several months of the index procedure.^1,2 We report an unusual presentation of extremely late DES stent fracture manifesting as acute myocardial infarction (MI) 6 years following the stent implant. The patient was managed successfully by coronary artery bypass grafting (CABG).

Case Report

A 63-year-old non-diabetic, non-hypertensive, male patient underwent angioplasty and stenting of the proximal left anterior descending artery (LAD) with a 3 mm x 28 mm sirolimus-eluting stent (Cypher) deployed at 12 atm with a good angiographic result (Figures 1A and B). He was discharged on routine anti-ischemic therapy and dual antiplatelet therapy (aspirin and clopidogrel). After one year, clopidogrel was discontinued and other medications were continued.

The patient presented with an acute anterior wall ST-elevation myocardial infarction 6 years later, for which he was thrombolysed with streptokinase within 2 hours with good ST segment resolution. Coronary angiography at our institute (3 days following the MI) revealed a complete fracture of the stent at its middle part, with total separation of the 2 portions of the stent. The separated stent pieces in the mid LAD were easily visible during plain fluoroscopy (Figures 2A and B). The patient underwent CABG and successfully received a left internal mammary artery graft to LAD (Figure 3).

Discussion

With increasing number and complexity of coronary intervention cases, reports of coronary stent fractures are not infrequent.^1-3 The incidence of DES fracture in observational studies varies from 1% to 5%, while autopsy studies report a higher incidence, reflecting the fact that many cases, especially those with isolated strut fractures, may be detected only incidentally.⁴ More severe forms of fractures with complete transection are more often associated with adverse events like late thrombosis or restenosis. Though most cases of stent fractures occur within several months of implantation, rarely cases are known to occur even within a few days of the procdeure.^3,5-7 However, such a late occurrence of fracture with presentation as acute MI 6 years following the index procedure as occurred in our case is extremely rare.

Almost all cases of stent fracture in DES have been reported with sirolimus-eluting stents, as compared to paclitaxel-eluting stents. This is likely because of the closed cell design in sirolimus-eluting stents, which makes the stent less conformable, creating multiple hinge points during cardiac contraction that may be prone to fracture over time.³ In our case too, the fracture involved a 3 mm x 28 mm Cypher stent, which is a sirolimus-eluting stent.

Though the exact mechanism responsible for stent fracture is not well understood, specific anatomic and technical factors play an important role. Overexpansion may lead to stretching and deformation while mechanical fatigue in areas of coronary artery tortuosity or excessive artery motion leads to constant compression, kinking and shearing, predisposing to fracture. Hence, stent fractures are most commonly reported in the right coronary artery (related to its mobility), overlapping and long stents, those deployed at high inflation pressure, or in vein grafts.^3,8 Though our case had a 28 mm long Cypher stent implanted in the LAD, the exact cause of stent fracture remains conjectural. It is possible that slight changes in vessel angulation, which occur after stent implantation, may create a distorting force predisposing to stent fracture over time. Although intravascular ultrasound and multislice computed tomography are considered more sensitive than routine coronary angiography to establish the diagnosis and mechanism of stent fracture, often (as also in our case), diagnosis is evident even on plain fluoroscopy, especially when the fracture is complete.

There is no consensus about the best treatment modality related to DES fracture. We did not elect to implant another stent due to the possible recurrence of the fracture and decided to refer the patient for CABG. He received a left internal mammary artery graft to the LAD, and is asymptomatic at 6 months follow-up.

Conclusion

The present case demonstrates that DES stent fracture may occasionally occur very late following stent implantation, and present as acute MI. It is possible that hitherto unrecognized factors may play a role in the genesis of stent fracture. Future designs for DES stent platforms and preclinical fatigue testing should work actively on reducing the rates of stent fracture. Since the incidence of stent fracture for future generation DES is likely to differ from the first-generation DES, clinical trials should also include appropriate end points to accurately ascertain the pattern of stent strut fracture.

Acknowledgment. We would like to acknowledge the kind help rendered by Dr. Sudeep Kumar associate professor, Department of Cardiology, Sanjay Gandhi PGIMS, Lucknow, India and Dr. Shantanu Pandey, associate professor, Department of Cardiothoracic Surgery, Sanjay Gandhi PGIMS, Lucknow, India.

References

1. Aoki J, Nakazawa G, Tanabe K, et al. Incidence and clinical impact of coronary stent fracture after sirolimus-eluting stent implantation. Catheter Cardiovasc Interv. 2007;69(3):380-386.
2. Popma JJ, Tiroch K, Almonacid A, Cohen S, Kandzari DE, Leon MB. A qualitative and quantitative angiographic analysis of stent fracture late following sirolimus-eluting stent implantation. Am J Cardiol. 2009;103(7):923-929.
3. Lee MS, Jurewitz D, Aragon J, Forrester J, Makkar RR, Kar S. Stent fracture associated with drug-eluting stents: clinical characteristics and implications. Catheter Cardiovasc Interv. 2007;69(3):387-394.
4. Nakazawa G, Finn AV, Vorpahl M, et al. Incidence and predictors of drug-eluting stent fracture in human coronary artery: a pathologic analysis. J Am Coll Cardiol. 2009;54(21):1924-1931.
5. Mehrle A, Skelton T, Almonacid A. Stent fracture: an unusual cause of late restenosis after sirolimus-eluting stent placement. Catheter Cardiovasc Interv. 2007;69(7):988-991.
6. Kang WY, Kim W, Kim HG, Kim W. Drug-eluting stent fracture occurred within 2 days after stent implantation. Int J Cardiol. 2007;120(2):273-275.
7. Park JS, Shin DG, Kim YJ, Hong GR, Cho IH. Acute myocardial infarction as a consequence of stent fracture and plaque rupture after sirolimus-eluting stent implantation. Int J Cardiol. 2009;134(2):e79-81.
8. Chakravarty T, White AJ, Buch M, et al. Meta-analysis of incidence, clinical characteristics and implications of stent fracture. Am J Cardiol. 2010;106(8):1075-1080.

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From the Department of Cardiology, Sanjay Gandhi PGIMS, Lucknow, India.
Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. The authors report no conflicts of interest regarding the content herein.
Manuscript submitted September 27, 2011, provisional acceptance given October 6, 2011, final version accepted November 14, 2011.
Address for correspondence: Aditya Kapoor, Dept. Of Cardiology, Sanjay Gandhi PGIMS, Lucknow 226014, India. Email: akapoor65@gmail.com