Stent thrombosis risk factors

# Overview
A number of clinical, angiographic, and procedural factors increase the risk of stent thrombosis. Predictors of stent thrombosis can be classified into anatomic variables, procedure related variables and clinical variables. ASA and clopidogrel resistance are  emerging risk factors for stent thrombosis.

# Risk Factors

## Procedure Related Variables
Procedure related variables associated with an increased risk of stent thrombosis include .:
- Stent underexpansion
- Dissections at the stent margin
- Incomplete wall apposition
- Residual inflow and outflow disease
- Overlapping stents
- Polymer materials
- Self expanding or coil stents

## Anatomic Variables
Lesion-specific factors that increase the likelihood of stent thrombosis include.:
- A residual dissection at the margin of the stent
- Impaired flow into or out of the stent
- Small stent diameters (<3 mm)
- Long stent lengths
- A thrombus containing lesions such as that observed in the treatment of an acute myocardial infarction

## Clinical Variables
Clinical variables include. :
- Acute myocardial infarction
- Noncompliance and discontinuation of clopidogrel,
- Hyporesponsiveness to antiplatelet agents
- Higher baseline platelet count
- Diabetes mellitus
- Renal failure
- Congestive heart failure
- Prior radiation  orbrachytherapy
Off-label indication of BMS and DES:
In addition to these, stent implantation for off-label indication of both DES and BMS(such as restenotic lesions, bypass graft lesions, left main coronary artery disease, as well as ostial, bifurcated, and totally occluded lesions) has been associated with higher rates of ischemic complications, including stent thrombosis, as compared with standard indications.
- In a case control study of 145 patients with stent thrombosis by Rinaldi et al, presence of angiographic thrombus prior to stenting, greater total stent length, higher baseline platelet count, acute MI indication, the use of a self expanding or coil stent, and GpIIb-IIIa exposure were identified as the strongest predictors of stent thrombosis.
- In another study by Marroquin et al to compare the outcomes in bare-metal versus drug-elting stents for off-label indications showed that one year after intervention, there were no significant differences in the adjusted risk of death or myocardial infarction in patients with drug eluting stents as compared with those with bare metal stents. These findings implicate that the poorer outcome observed after stenting for off-label indications are related to patient and lesion characteristics but not to the stent itself. Therefore, large randomized clinical trial are needed to further study the use of DES for off label versus standard indications.

## Risk Factors for Early and Late Stent Thrombosis
- Premature discontinuation of antiplatelet/clopidogrel
- Clopidogrel resistance: Absence/dysfunction of CYP2C19 allele which is required for the conversion of clopidogrel to its active metabolite.
- Improper opposition of the stent or undersized stent
- Length of the stent- greater the length, higher the risk
- Malignancy
- Cocaine use
- Small caliber of the vessels
- Slow intra coronary flow post PCI
- Bifurcation lesion
- Inadequate periprocedural anticoagulation
- Low ejection fraction (<30%)
- Nonionic contrast media
- Prior brachytherapy
- Small stent area on intracoronary ultrasound
- Residual plaque/thrombus/dissection after stent placement
- CAD 50% proximal of culprit lesion
- Chronic kidney disease
- Diabetes mellitus
- Black race
- Elevated C-reactive protein levels
- Hypersensitivity to stents
- Young age
- Paclitaxel-eluting stent implantation
- Multivessel disease
- Acute coronary syndrome at presentation

## Risk Factors for Very Late Stent Thrombosis
- Ongoing vessel inflammation
- Delayed neointimal coverage which is usually seen with DES when compared to BMS