Modern coronary stents fail in roughly 5 to 10% of cases within the first year, a dramatic improvement over older designs that failed up to a third of the time. “Failure” can mean two different things: the artery gradually re-narrows around the stent (restenosis), or a blood clot suddenly forms inside it (thrombosis). Both have distinct timelines, risk factors, and warning signs.
Restenosis: The Most Common Type of Failure
Restenosis happens when tissue regrows inside or at the edges of a stent, slowly choking off blood flow again. With older bare-metal stents, this was a serious problem. Clinical trials found restenosis rates of 29 to 32% within nine months of placement. That meant roughly one in three patients ended up with a re-narrowed artery.
Drug-eluting stents, which release medication to suppress tissue growth, changed the picture significantly. In the landmark SIRIUS trial, the restenosis rate inside the stent dropped to 2% with a drug-coated design compared to 32% with bare metal. Even accounting for narrowing at the stent edges, the overall restenosis rate was about 9%, and only 7% of patients needed a repeat procedure. Later trials of different drug coatings showed similar improvements, with repeat intervention rates around 5% at one year versus 16% for bare metal.
These numbers mean that with current technology, somewhere between 5 and 10 out of every 100 patients will develop meaningful restenosis. It typically shows up within the first 6 to 12 months, though a different, slower process can cause problems years later.
Stent Thrombosis: Rarer but More Dangerous
Stent thrombosis is a blood clot forming inside the stent, and it can trigger a sudden heart attack. It’s far less common than restenosis but more immediately dangerous. An analysis of over 8,700 patients from the ATLAS ACS 2-TIMI 51 trial broke down the risk by time period:
- First 30 days (early thrombosis): 0.80%
- 1 to 12 months (late thrombosis): 0.81%
- 12 to 24 months (very late thrombosis): 0.77%
Over two years, the cumulative rate was about 2.25%. What’s notable is how evenly the risk spreads across time. Unlike restenosis, which clusters in the first year, thrombosis remains a low but persistent threat well beyond the initial recovery period. This is a key reason doctors prescribe blood-thinning medications for months or longer after stent placement.
Why Stents Fail Years Later
A stent that works perfectly for years can still eventually fail through a process called neoatherosclerosis. Essentially, new plaque builds up inside the stented segment of the artery, mimicking the original disease that required the stent in the first place.
Here’s what happens at a cellular level: the drugs on modern stents suppress tissue growth, which is how they prevent early restenosis. But that same suppression slows the artery’s ability to form a healthy new inner lining. Without that lining, immune cells called macrophages accumulate, absorb fats, and form the beginnings of new plaque. Over time, this plaque can develop a thin outer cap that’s prone to rupturing, potentially triggering a clot or heart attack. Tiny areas of calcification and microbleeding where the rigid stent meets the softer artery wall add to the instability. This process is now recognized as a significant driver of stent problems that appear years after implantation.
Peripheral Artery Stents Fail More Often
Stents placed in leg arteries face a tougher environment than those in the heart. The arteries running through the thigh and behind the knee bend, twist, and compress with every step. That mechanical stress takes a toll. In a registry of 604 patients who received stents in these leg arteries, 4.3% developed stent thrombosis. Covered stent grafts fared worse, with thrombosis in nearly 11% of cases.
Patients who developed leg stent thrombosis had significantly worse outcomes. Within 12 months, 42% of them needed an unplanned repeat procedure, emergency surgery, or major amputation, compared to 19% of those whose stents remained open. If you’ve had a peripheral stent placed, persistent or returning leg pain, numbness, or skin color changes in the affected leg are signs worth taking seriously.
What Raises Your Risk
Diabetes is one of the strongest predictors of stent failure. A large study in the Journal of the American College of Cardiology looked specifically at blood sugar control in people with type 2 diabetes. Compared to patients with moderately controlled blood sugar, those with poorly controlled diabetes had a 25 to 46% higher risk of stent failure, with risk climbing in a dose-response pattern as blood sugar control worsened. Even modestly elevated levels increased the hazard by 25%.
Other well-established risk factors include smoking, which damages artery linings and promotes clot formation, and stopping blood-thinning medications too early. The 2025 guidelines from the American College of Cardiology and American Heart Association recommend staying on dual antiplatelet therapy (typically aspirin plus a second blood thinner) for at least 12 months after stent placement in patients who had an acute coronary event and aren’t at high bleeding risk. Stopping one of these medications in the first few months is one of the strongest predictors of stent thrombosis.
Other factors that increase the odds of failure include small vessel diameter, long stented segments, stents placed at artery branch points, and having multiple stents. Some of these are within your control. Others are simply a function of your anatomy and the severity of your disease.
Recognizing Stent Failure
Restenosis often feels like a return of the original symptoms: chest pain or pressure during exertion, shortness of breath, nausea, or pain radiating to the shoulder or arm. These symptoms typically develop gradually as the artery re-narrows over weeks or months. Some people with restenosis have no symptoms at all, and the problem is only discovered during routine follow-up testing.
Stent thrombosis is different. Because a clot can block the artery suddenly, it often presents as a heart attack, with severe chest pain, sweating, and shortness of breath that comes on quickly. This is a medical emergency.
When stent failure is suspected, the most common initial test is a stress test to see how well blood flows to the heart during exertion. If results are concerning, imaging of the coronary arteries can confirm whether the stent has re-narrowed or clotted. Treatment usually involves either re-opening the stent with a balloon, placing a new stent inside the old one, or in some cases, bypass surgery.