Coronary stents are small, tube-shaped devices placed in the heart’s arteries to treat coronary artery disease, a condition where plaque buildup narrows these vessels and restricts blood flow. Stents help to keep the arteries open, improving blood flow to the heart and reducing symptoms like chest pain. While generally successful, stent implantation can sometimes lead to complications, one of which is stent thrombosis. This occurs when a blood clot forms within the stent, and when it happens a significant time after the procedure, it is referred to as late stent thrombosis.
Understanding Late Stent Thrombosis
Late stent thrombosis refers to the formation of a blood clot inside a coronary stent that occurs between 30 days and one year after the stent was implanted. This complication can lead to serious events, including heart attack or cardiac death. Stent thrombosis is categorized by the time elapsed since the stent placement.
Acute stent thrombosis occurs within 24 hours of the procedure, while subacute stent thrombosis happens between 24 hours and 30 days post-implantation. Beyond the one-year mark, the event is classified as very late stent thrombosis.
Factors Contributing to Late Stent Thrombosis
Several factors contribute to the occurrence of late stent thrombosis, stemming from both the biological response to the stent and patient-specific conditions. One primary mechanism is delayed arterial healing, especially observed with drug-eluting stents (DES). These stents release medication to prevent excessive tissue growth that could re-narrow the artery, but this can also delay the natural healing process where the stent struts become covered by a new layer of endothelial cells. Incomplete strut coverage leaves parts of the stent exposed to blood, increasing the risk of clot formation.
Another significant contributor is neoatherosclerosis, the formation of new plaque within the stent. This process can lead to plaque rupture and subsequent thrombus formation, even years after stent implantation. Inflammation within the stented segment can also contribute to this new plaque development and increase thrombotic risk.
Mechanical issues related to the stent’s placement or integrity can also play a role. Incomplete stent apposition, where a stent strut is not fully pressed against the artery wall, can create an area of stagnant blood flow that promotes clot formation. Stent fracture, a break in the stent’s structure, is another mechanical problem that can lead to thrombosis by disrupting blood flow or exposing thrombogenic surfaces.
Patient-related factors also significantly influence the risk of late stent thrombosis. Non-adherence to prescribed dual antiplatelet therapy (DAPT), which typically involves aspirin and a P2Y12 inhibitor, is a major preventable cause. These medications prevent platelets from clumping together and forming clots within the stent. Conditions like diabetes and chronic kidney disease are also associated with an increased risk of stent thrombosis, likely due to their effects on blood vessel health and clotting mechanisms.
Signs and Management of Late Stent Thrombosis
Late stent thrombosis often manifests with symptoms similar to an acute heart attack. Individuals may experience sudden chest pain or discomfort, which can spread to the arms, back, stomach, neck, or jaw. Other symptoms can include shortness of breath, lightheadedness, dizziness, nausea, and sweating. Stent thrombosis often presents as a severe type of heart attack.
Upon presentation with these symptoms, immediate medical evaluation is necessary. Diagnosis typically involves an electrocardiogram (ECG) to assess heart electrical activity and blood tests to measure cardiac enzymes. Coronary angiography is often performed to directly visualize the coronary arteries and confirm the presence of a blood clot within the stent.
The immediate management of late stent thrombosis usually involves emergency percutaneous coronary intervention (PCI). This procedure aims to re-open the blocked artery, often by using a balloon to expand the stent and restore blood flow. In some cases, aspiration thrombectomy, which involves removing the blood clot, may be performed. Thrombolytic therapy, using medications to dissolve the clot, can be an alternative in facilities without immediate access to a catheterization laboratory.
Strategies to Reduce Risk
Reducing the risk of late stent thrombosis involves a combination of consistent medical adherence and lifestyle adjustments. Adherence to dual antiplatelet therapy (DAPT) is a primary preventative measure. Patients are typically prescribed aspirin indefinitely and a P2Y12 inhibitor for a recommended duration, often 6 to 12 months or longer, depending on the stent type and individual risk factors. Consistent use of these medications helps prevent blood clots from forming within the stent.
Lifestyle modifications also play a significant role in long-term prevention. Quitting smoking is important, as smoking damages artery linings and promotes plaque buildup. Managing blood pressure and cholesterol levels through diet, exercise, and medication can reduce the progression of atherosclerosis. Controlling diabetes through diet and medication is also important, as it is a known risk factor for stent thrombosis.
Maintaining a healthy weight and engaging in regular physical activity contribute to overall cardiovascular health. From a procedural standpoint, optimal stent deployment techniques by the physician, ensuring the stent is fully expanded and well-apposed to the artery wall, are also important in minimizing future complications. Careful selection of the appropriate stent type based on patient characteristics and lesion complexity further contributes to reducing the risk of late stent thrombosis.