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Low recurrent stenosis after coronary silicon carbide coated cobalt chromium stent
By QCA, the angiographic in-stent diameter stenosis (DS) was
reduced significantly: from 68.9±18.2% to 15.72±9.6%
immediately after stent angioplasty (p=0.0061), and to 42.0±23.4%
at follow-up (p=0.018*) (*as compared to baseline). The in-stent
minimum lumen diameter (MLD) increased significantly: from
0.84±0.48 mm to 2.30±0.62 mm immediately after stent
angioplasty (p=0.0089), and to 1,58±0.87 mm at follow-up
(p=0.012*) (*as compared to baseline). Therefore the in-stent late
loss (LL) was 0.75±0,71 mm (LL in-segment: 0.79±0,72 mm).
Discussion
The optimal behaviour of a stent material regarding its interaction
with the environment is achieved if complete endothelialisation with
a long-term stable and fully functional layer of endothelial cells is
guaranteed within several days. Sound endothelial cells, being the
natural interface between blood and the vessel wall, are in a way the
perfect coating for a stent. On the one hand, they behave passively
with regard to proteins of the coagulation cascade and platelets. On
the other hand, they are key players in the mechanisms controlling
the growth of smooth muscle cells. Laboratory findings and relatively
small clinical studies have disclosed that stent surface rapidly
differentiating into a functional endothelial layer can influence the
angioplasty-related restenotic process
10
, which consists of a range of
different constituents
35
. These findings include the fact that
a functional endothelial layer inhibits smooth muscle migration and
proliferation, and reduces the formation of extra-cellular matrix
proteoglycans which provides cellular migration
36,37
. However no
data have yet been published whether stent surfaces may influence
the constrictive arterial remodelling following balloon angioplasty (i.e.
adventitial collagen accumulation and subsequent thickening) which
can be prevented by matrix metalloproteinase inhibition
38
. But the
degree of biocompatibility of the stent surface can induce restenosis
on the basis of persistent platelet activation, which in turn inactivates
endothelial relaxation factors.
In vitro
studies showed that after 24 hours of contact between the
CPAE and 316L stainless steel, no continuous endothelial layer had
formed (Figure 2a)
23
. The majority of cells had no contact with their
direct neighbour. The single endothelial cells showed marked
pseudopodia with lengths of about 1 µm (Figure 2b)
23
. In contrast to
these observations, the situation is completely different on the a-
SiC:H coated samples. During the same time and under the same
experimental conditions, a continuous endothelial layer covering the
whole sample had developed (Figure 3a). The single endothelial
cells showed a sound spindle-like shape and the endothelium itself
had a characteristic pavement structure including cell-to-cell
contacts between neighbouring cells (Figure 3b)
23
.
Exactly these SiC:H-effects
in vitro
potentially explain our
encouraging clinical results in this study: Through accelerating
rapid endothelialisation to an earlier functional layer, SiC:H -coating
on ultra-thin cobalt chromium stents leads to less recurrent stenosis
after stent placement without increased occurrence of stent
thrombosis. In this study, not only the clinically driven TLR
(intention-to-treat) appeared very low, but the late loss assessed by
QCA was 0.75 mm which is almost exactly the value seen after
placement of the Endeavor drug eluting stent
39
.
Figure 2. Endothelial cells (CPAE) after 24 hours of contact with 316L
stainless steel in modified Eagle medium: (a) Light microscopy image
showing only isolated cells on the surface. (b) AFM image showing
endothelial cells with marked pseudopodia.
Figure 3. Endothelial cells (CPAE) after 24 hours of contact with
silicon carbide (a-SiC:H) coated stainless steel in modified Eagle
medium: (a) Light microscopy image showing an endothelial layer
covering the silicon carbide completely. (b) AFM image showing
endothelial cells with characteristic pavement structure.