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.