Cardiovascular stents - Biomaterials and Devices for the Circulatory System - page 172

C
Closed stent

Coronary artery

Plaque

Balloon catheter

(a)

Expanded stent

Inflated balloon

(b)

Plaque compressed by stent

(c)

Stent widens artery allowing increased blood flow

7 . 3 Diagrammatic representation of stent deployment. The balloon
catheter is inserted into the artery (a) and the balloon infl ated to
expand the stent (b). The balloon is then defl ated and the catheter
withdrawn to leave the stent in place to hold the artery open (c).
(Adapted from http://www.radiology.ucsf.edu/sites/docs/radiology.ucsf.
edu.ir/fi les/stent.jpg.)

Sub-acute stent thrombosis can be divided into device-related and patient-
related thrombosis. Device-related thrombosis can be caused by either surface
interaction between the blood components and the metallic stent surface or
due to the nature of fl ow in the vessel (rheological factors). The patient-
related factors are subdivided into: (a) vessel size-related thrombosis where
the smaller calibre vessels have an increased risk of thrombosis, (b) lesion
characteristics such as lesion length and amount of atherosclerotic plaque and
(c) anatomic location of the stent (the risk of thrombosis is higher in the left
anterior descending (LAD) coronary artery and lowest in the saphenous vein
grafts. Technique-related factors are also important as optimally deployed
stents give favourable rheological factors, which can otherwise trigger the
coagulation cascade and, therefore, clotting formation (Kutryk et al. , 1999).
However, despite their success at improving the treatment of coronary
and peripheral artery disease, the occurrence of thrombosis and vascular
injury upon implantation can result in restenosis, the re-narrowing of the
target coronary artery (Liu et al. , 1989). Restenosis remains the main limita-
tion associated with the deployment of a stent. This type of drawback
is called in-stent restenosis (ISR) to distinguish it from the PTCA-
induced restenosis (Lowe et al. , 2002). ISR with subsequent target vessel

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