Stent thrombosis is the sudden formation of a blood clot inside a coronary stent, the small mesh tube placed to hold a narrowed heart artery open. It usually blocks the artery completely and presents as a heart attack, so it is a medical emergency treated with urgent angioplasty and intensive antiplatelet therapy. It is uncommon with modern stents, and the single most important way to prevent it is taking antiplatelet medicines exactly as prescribed after the procedure.
Although cardiologists manage the procedure, stent thrombosis is fundamentally a problem of platelets and clotting, which is why it sits squarely in hematology teaching too. This article explains why it happens, how it is recognized, and how it is treated and prevented.
What Is Stent Thrombosis?
During percutaneous coronary intervention (PCI), a balloon opens a narrowed coronary artery and a metal stent is left behind as scaffolding. Until the artery lining heals over it, the stent surface is exposed to flowing blood and can attract platelets.
If platelets and fibrin build up on the stent, they can block the artery abruptly. The mechanisms mirror those behind native vessel clots, explained in our article on the pathogenesis of coronary thrombosis.
Classification by timing
Stent thrombosis is grouped by when it occurs after the stent is placed, because the likely causes differ at each stage.
| Category | Timing after stenting | Most common drivers |
|---|---|---|
| Acute | Within 24 hours | Procedural issues such as dissection, underexpansion, or residual clot |
| Subacute | 24 hours to 30 days | Stent underexpansion or malapposition, early stopping of antiplatelet drugs |
| Late | 30 days to 1 year | Stopping antiplatelet therapy, incomplete healing of the artery lining |
| Very late | More than 1 year | Delayed healing, inflammation, new plaque inside the stent (neoatherosclerosis) |
Acute and subacute events are often grouped together as early stent thrombosis. Clinicians also grade certainty as definite (confirmed on angiography or pathology), probable, or possible.
Causes and Risk Factors
Stent thrombosis almost always results from a combination of factors. They are usually sorted into three groups.
Patient factors
- Premature stopping of antiplatelet therapy, the strongest and most preventable risk factor
- Presentation with an acute coronary syndrome rather than stable angina
- Diabetes, chronic kidney disease, and reduced heart pump function
- Smoking
- Hypercoagulability, including cancer and inherited or acquired clotting tendencies
- Poor response to clopidogrel, which varies between individuals
Procedural factors
- Stent underexpansion, where the stent is not fully opened
- Stent malapposition, where the stent struts do not sit against the artery wall
- Edge dissection or untreated disease at the stent margins
- Long stented segments, small vessels, and overlapping stents
Stent and lesion factors
The stent surface, polymer coating, and drug release affect how quickly the artery heals. Modern drug-eluting stents have thinner struts and more compatible coatings than earlier designs, which has lowered thrombosis risk. Complex lesions, such as bifurcations or heavily calcified arteries, remain higher risk.
How the Clot Forms
Stenting injures the artery wall and exposes collagen and tissue factor. Platelets stick to this surface, become activated, and release ADP and thromboxane A2, which recruit more platelets. The receptors on their surface then bind fibrinogen, linking platelets together in platelet aggregation. The clotting cascade adds fibrin to stabilize the clot.
This explains why treatment relies on two antiplatelet drugs: aspirin blocks thromboxane production, and a P2Y12 inhibitor such as clopidogrel, prasugrel, or ticagrelor blocks the ADP receptor. Together they are called dual antiplatelet therapy (DAPT).
Symptoms and Diagnosis
Because the artery usually closes suddenly, stent thrombosis most often presents as an acute heart attack, frequently an ST-elevation myocardial infarction (STEMI). Typical symptoms include:
- Sudden crushing or pressure-like chest pain, sometimes spreading to the arm, jaw, or back
- Shortness of breath
- Sweating, nausea, or lightheadedness
- Collapse or cardiac arrest in severe cases
An electrocardiogram (ECG) and blood troponin confirm heart muscle injury. Coronary angiography confirms the diagnosis by showing a clot in the stent. Intracoronary imaging with intravascular ultrasound (IVUS) or optical coherence tomography (OCT) helps identify mechanical causes, such as underexpansion, so they can be corrected.
Treatment and Prevention
Emergency treatment
The priority is reopening the artery as quickly as possible with emergency PCI. The cardiologist may use balloon angioplasty, remove clot, and correct any mechanical problem with further balloon inflation or an additional stent.
Medications given at the same time include aspirin, a potent P2Y12 inhibitor, and an anticoagulant such as heparin. In selected cases, a glycoprotein IIb/IIIa inhibitor is added for stronger short-term platelet blockade.
Long-term prevention
- Take DAPT without interruption. Duration is individualized, commonly around 6 months after planned stenting for stable disease and around 12 months after an acute coronary syndrome, then usually a single antiplatelet drug long term.
- Never stop antiplatelet drugs without speaking to your cardiologist, including before dental work or surgery.
- Control risk factors: stop smoking, manage diabetes, blood pressure, and cholesterol, and stay active.
- Balance bleeding risk: people at high bleeding risk may receive shorter DAPT, and this decision is made by the treating team.
For an overview of clotting problems beyond the heart, see our blood clotting guide.
Frequently Asked Questions
How common is stent thrombosis today?
It is uncommon with current drug-eluting stents and good antiplatelet adherence. The risk is highest in the first month after the procedure and falls after that.
Can I stop my blood thinners if I need surgery?
Not on your own. Stopping antiplatelet therapy early is the strongest known trigger of stent thrombosis. Your surgeon and cardiologist should agree a plan, and elective surgery is often delayed until the minimum DAPT period is complete.
Is stent thrombosis the same as restenosis?
No. Restenosis is gradual re-narrowing of the stent from scar tissue growth over months, usually causing slowly returning angina. Stent thrombosis is a sudden clot that typically causes a heart attack.
Can stent thrombosis happen years later?
Yes, although it is rare. Very late stent thrombosis is linked to delayed healing, inflammation, or new plaque inside the stent, which is why long-term risk factor control matters.
Key Takeaways
- Stent thrombosis is a clot inside a coronary stent and usually presents as a heart attack.
- It is classified as acute, subacute, late, or very late, and the causes differ by timing.
- Premature stopping of antiplatelet therapy is the most important preventable cause.
- Treatment is emergency PCI with intensive antithrombotic therapy, guided by intracoronary imaging when possible.
- Anyone with a stent who develops sudden chest pain should call emergency services immediately.
