Cardiovascular stents - Biomaterials and Devices for the Circulatory System - page 188

titanium-nitride oxide stents resulted in comparable clinical outcomes
when compared with paclitaxel eluting stents in patients treated for acute
myocardial infarction (Karajalainen et al. , 2008) and more recently report
on the two and three year follow-up study on patients treated for acute MI
have indicated an improved clinical outcome following implantation of the
TITANOX stent compared with paclitaxel eluting stents (Karjalainen
et al. , 2009a) and reduced the need for target vessel revascularisation
(Karajalainen et al. , 2009b).

7.5 Radioactive stents

Restenosis occurs in between 20 and 50% of patients fi tted with a bare
metal stent, depending on the patient and lesion (Kutryk et al. , 2007). To
date the only way to overcome this problem to any signifi cant degree has
been to use either drug eluting stents or brachytherapy using radioactive
stents to treat the restenosis itself by killing cells that have re-occluded the
stent and to prevent the re-growth of the tissue. The fi rst radioactive stents
were produced in the early 1990s in which stainless steel stents were ren-
dered radioactive by bombardment with charged particles transforming
some of the elements within the steel into radioisotopes (Hehrlein et al. ,
1993; Fischell et al. , 1994).
Since then radioactive stents have promised the advantage of delivering
radiation, either

γ or β , at a continuous low dose rate and studies in the

1990s suggested that -particle emitting stents were able to successfully

prevent in-stent restenosis (Hehrlein et al. , 1995, 1996; Wardeh et al. , 1999).
Furthermore, this therapeutic approach was reported in a number of ran-
domised clinical trials nearly a decade ago to result in a signifi cant reduction
in angiographic and clinical restenosis in patients receiving treatments for
both de novo lesions and for in-stent restenosis with decreased neointima
formation due to the prevention of SMC proliferation and migration
(Raizner et al. , 2000; Teirstein et al. , 2000; Waksman et al. , 2000a, b). However,
it has also been suggested that the effects of delivering continuous low dose
rates of radiation may have adverse effects. The initial radioactivity may
raise the body's phosphorus levels, thus enhancing the device corrosion
process and consequently impairing its long-term biocompatibility
(Hehrlein et al. , 1995). In addition, studies using half radioactive stents
dosed with 32 P compared with non-radioactive control stents showed a
signifi cant neointimal thickening at the mid-stent dose fall-off zone of the
radioactive stents although not at the stent-to artery transitional areas at
the extremities of the implant. It was concluded that in this study the edge
effect seen with high dose radioactive stents could be related to a combina-
tion of the stent injury and the radioactive dose fall-off (van der Geissen
et al. , 2001). Furthermore, three clinical reports published at the start of the

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