Discussion
ST is a rare but devastating complication of PCI with up to 50%
mortality rate in early cases . ST can be caused by various mechanisms:
patient-related, pharmacologic, procedure-related, postprocedural, and
lesion-related factors . Acute coronary syndrome (ACS), reduced kidney
function (considering GFR), history of previous coronary artery disease
(CAD), uncontrolled hypertension, and hyperlipidemia were among the
possible patient-related factors causing stent thrombosis in our case.
However, a meta-analysis on factors impacting ST questioned the clinical
significance of baseline characteristics in terms of predicting ST in
patients undergoing PCI due to high heterogeneity in outcomes .
Stent under-expansion, stent under-sizing, geographic miss, edge
dissection, in-stent tissue protrusion/prolapse, acute stent
malapposition, stent fracture, longitudinal stent deformation, and
non-uniform strut distribution are stent-related problems which can
cause ST and can be detected by intravascular imaging like IVUS and OCT
. We detected stent underexpansion in IVUS imaging of our patient,
despite the sufficient postdilation performed 2 weeks ago after stent
implantation.
IVUS is an imaging modality used to characterize lesion morphology,
quantify plaque burden, guide stent sizing, assess stent expansion,
and identify procedural complications by obtaining a 360-degree view of
the vessel . IVUS played a key role in the diagnosis of stent thrombosis
in our case, which seemed to be the result of procedure-related, as well
as patient-related factors.
Randomized trials have demonstrated that an IVUS-guided
revascularization strategy compared with angiography-guided PCI can lead
to improved clinical outcomesand is associated with a reduction in major
adverse cardiovascular events (MACE) .This was explained with more
postdilation and larger stent sizes, final larger angiographic minimal
lumen diameters, and larger minimal stent areas while using IVUS, which
minimized stent underexpansion. Also, more stents were implanted and
longer stents were used with IVUS guidance to minimize geographic miss
and treat edge dissections .
Stent underexpansion is a major risk factor of stent thrombosis, defined
as when the stent doesn’t reach nominal stent size but stent struts
reach the vessel wall. Post-PCI inadequate minimal stent area (MSA) is
consistently the strongest predictor of stent thrombosis .
A meta-analysis of randomized trials of IVUS vs. angiographic guided
bare metal stent (BMS) implantation (n=2193 patients) revealed that IVUS
guidance was associated with a significantly larger post-procedure
angiographic minimum lumen diameter, as well as, a significantly lower
rate of angiographic restenosis (22.2% vs.28.9%,p=0.02), repeated
revascularization (12.6% vs. 18.4, p=0.004), and overall MACE (19.1%
vs. 23.1%;p=0.03) .Therefore, checking for adequate expansion also good
apposition with IVUS can be of great help in preventing the disastrous
consequences of stent thrombosis.