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Coronary Stent Fracture: The Hidden Truth of a Problem More Common Than Stent Thrombosis

The report by Hetterich and Rieber in this issue of CCI adds additional focus on the problem of coronary stent, specifically strut, fracture [1]. Their case report illustrates fractures in long and overlapping sirolimus-eluting stents in an area of the coronary tree with above average angulation and flexion. From this report and others, there are some pressing questions that must be asked with the goal to further improve stent technology and its optimal use.

  1. Are coronary stent fractures rare? Aoki detected fractures in 2.6% of lesions in patient undergoing routine follow-up angiography after stenting [2]. Shaifh reported that 20% of patients with DES in-stent restenosis have stent fractures [3].
  2. Are coronary stent fractures bad for the patient? The association between stent fracture and restenosis is strong. The numerous case studies illustrate the negative clinical consequences of stent fracture. What is unclear is whether there are many stent fractures that are undetected and without any clinical sequelae.
  3. What is the best treatment for a stent fracture? It is remarkable, as in this case, how an additional stent is often placed to treat restenosis that may be a result of stent fracture. This may seem reasonable if restenosis is viewed in isolation without recognizing stent fracture or as a consequence of no drug-eluting struts in the area of the focal restenosis process. On the other hand, the local hostile mechanical environment causing the original fractures will still be present unless the underlying myocardium stops contracting and the artery is no longer subjected to these forces.
  4. Are coronary stent fractures easily detected? The answer is clearly no and leads to the conclusion that stent fracture is underreported. This underreporting is not unexpected since current coronary stents are minimally radiopaque. Furthermore, coronary arteries and stents are small and move constantly such that visualization requires an imaging modality with very high spatial and temporal resolution.
  5. Is stent fracture more common in SES? The answer to this question, based on literature reports is yes, but it is apparent that stent visibility for SES versus PES is better and thus there is an inherent bias against SES in the detection of fractures. True rates of fracture of different stent designs must await studies that include a surveillance technique applied to a larger number of patients with an imaging modality that will detect most if not all fractures even in stents with a low radiopacity.
  6. What imaging modality should be used to detect stent fractures? The only modality that is widely available and has the potential for showing in vivo stent fractures is X-ray. Trehan nicely described the triad needed for stent fracture visualization with present day technology: the fracture must be moderate to severe, the stent must be reasonably radiopaque, and the patient cannot be too obese [4]. Of note is that standard IVUS is not suitable for detection of stent fracture despite its widespread use for assessment of stent expansion and apposition.
  7. Since a much more sensitive means of detecting stent fracture is needed, what improvements in X-ray visualization are possible? Enhanced stent visualization has been pursued by development groups and studied clinically [5,6]. Unfortunately easily detectable markers, currently only on the delivery system, are needed for motion compensation to enhance stents and reduce quantum noise. This requirement makes the process only applicable to the minutes in the immediate post-implantation period. We need a technique that will allow enhancement of implanted stents in outpatient based surveillance studies. Permanent markers at the proximal and distal ends of stents could be used as one solution. Another limitation of current stent enhancement technologies is that they are 2D and thus the detection of fractures will be viewing angle dependent and fractures occurring on one side of a stent may be missed. Progress on 3D stent reconstruction is being made [7].
  8. Does the presence of fractures in approved stents implanted in patients mean that preclinical testing was inadequate? Bench-top testing relies on the setting of boundary conditions. It is challenging to estimate the unique mechanical stresses that are placed on medical devices that are implanted in the body. Our research group has performed studies trying to understand and quantify the unique physiologic changes in coronary shape during the cardiac cycle and the impact of stents on coronary shape [8,9]. Better preclinical testing should be designed with human data that can be obtained with improvements in coronary imaging and the ability to quantify unique forces like vessel twisting. Measurements taken at rest, though, will certainly not show us what happens during exercise in our patients with indwelling stents.
  9. Do we need a coronary stent surveillance program? Carter has suggested that prospective surveillance of coronary stents should be routine to detect the frequency, character, and clinical consequences of stent fracture [10]. This seems like a reasonable recommendation since we are clearly underreporting a clinically important complication from coronary stenting that needs to be better studied and used to improve stent design.
  10. Should you modify your practice today to reduce the chance of stent fracture? At this point it seems prudent to be aware of the settings in which fracture has been reported and consider stent fracture whenever you find restenosis. On the other hand, until we have better stent visualization tools and longitudinal studies, our understanding of stent fracture will remain as hidden and obscure as the stent fractures themselves.v

References

  1. Hetterich H and Rieber H. Multiple stent fractures at the site of coronary artery bypass insertion. Catheter Cardiovasc Interv 2008;72:??.
  2. Aoki J, Nakazawa G, Tanabe K, Hoye A, Yamamoto H, Nakayama T, Onuma Y, Higashikuni Y, Otsuki S, Yagishita A, Yachi S, Nakajima H, Hara K. Incidence and clinical impact of coronary stent fracture after sirolimus-eluting stent implantation. Catheter Cardiovasc Interv 2007;69:380–386.
  3. Shaikh F, Maddikunta R, Djelmami-Hani M, Solis J, Allaqaband S, Bajwa T. Stent fracture, an incidental finding or a significant marker of clinical in-stent restenosis. Cathet Cardiovasc Interv 2008;71:614–618.
  4. Trehan V, Nigam A, Bhamri N. Stent fracture: A biomaterial scientist’s responsibility or an interventionalist’s Onus? Indian Heart J 2007;59:5–8.
  5. Mishell JM, Vakharia KT, Portset TA, Yeghiazarians Y, Michaels AD. Determination of adequate coronary stent expansion using stentboost, a novel fluoroscopic image processing technique. Catheter Cardio Interv 2007;69:84–93.
  6. Perrenot B, Vaillant R, Prost R, Finet G, Douek P, Peyrin F. Motion correction for coronary stent reconstruction From rotational x-ray projection sequences. IEEE Trans Med Imag 2007;26:1412–1423.
  7. Movassaghi B, Schaefer D, Grass M, et al. 3D reconstruction of coronary stents in vivo based on motion compensated X-ray angiograms. Proc MICCAI 2006:177–184.
  8. Chen Sy and Carroll JD. Kinematic and deformation analysis of 4-D coronary arterial trees reconstructed. IEEE Transact Med Imaging 2003;22:710–721.
  9. Liao R, Chen SY, Messenger JM, Groves B, Burchenal J, Carroll JD. Four-dimensional analysis of cyclic changes in coronary artery shape. Cathet Cardiovasc Interv 2002;55:344–354.
  10. Carter A. Stent strut fracture: Seeing is believing. Cathet Cardiovasc Interv 2008;71:619–620.

Autor: John D. Carroll, MD

Fuente: Catheterization and Cardiovascular Interventions 73:88–89 (2009

Ultima actualizacion: 26 DE ENERO DE 2012

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