Stent thrombosis

A stent, like any foreign body in contact with blood, can cause thrombosis at the site of implantation. The stent surface has the ability to "attract" platelets, but after a short period of time, the metal surface is covered with precipitating proteins, which somewhat reduces the risk of stent thrombosis. After 2-4 weeks after HTIC implantation and several months after DES implantation, the protein film is covered with neointima, which dramatically reduces the risk of stent thrombosis.

Temporal characteristics of stent thrombosis

Type of thrombosis	Time of development
Spicy	0 24 h
Subacute	24 hours - 30 days
Late	30 days 1 year
Very late	After 1 year or more

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Causes of stent thrombosis

Risk factors for acute stent thrombosis are stenting in acute myocardial infarction, interventions on venous bypass grafts, failure to take ASA, clopidogrel the day before the procedure, as well as inadequate coagulation during PCI, and persistence of residual dissection. The main risk factors for subacute stent thrombosis are: persistence of residual dissection, thrombus, tissue protrusion through the stent cells into the vessel lumen, stenting of large and complicated lesions, as well as under-deployment of the stent, and discontinuation of antiplatelet agents.

The risk of stent thrombosis is increased in patients with ACS and type 2 diabetes mellitus. In patients with ACS, the most important risk factors for stent thrombosis are the severity of coronary artery disease, low hemoglobin levels, small diameter of the implanted stent, and the absence of thienopyridines before the procedure.

Among all stent thromboses, subacute (41%) and acute stent thromboses (32%) are the most common, with late and very late stent thromboses accounting for about 26% of all cases. In contrast to late thromboses, the incidence of acute and subacute stent thromboses is similar with LES and DES. In at least one study, heparin-eluting stents reduced the incidence of acute stent thromboses compared with conventional LES.

In early studies, in which the use of ASA, dipyridamole and warfarin was recommended after stenting, the incidence of stent thrombosis reached 20%, with bleeding often developing. It was later shown that in most cases, acute TS occurs due to under-deployment of the stent, which prompted the routine use of high pressure during stenting. In addition, the effectiveness of a 4-week course of dual antiplatelet therapy (ASA + ticlopidine) after stenting was proven. All these measures made it possible to reduce the incidence of acute and subacute stent thrombosis to less than 1%. The average time of subacute TS occurrence decreased from 6 to 1-2 days. At the same time, the exclusion of warfarin from the mandatory TS prophylaxis regimen reduced the incidence of hemorrhagic complications. Subsequently, ticlopidine was almost universally replaced by clopidogrel, since with the same effectiveness it is characterized by a lower incidence of adverse events.

Despite the decrease in incidence, stent thrombosis remains one of the most dangerous complications of stenting. As a rule, it manifests itself as a severe angina attack accompanied by ST segment elevation. In the STRESS study, mortality in subacute stent thrombosis was 20%, and in the remaining 80% of cases, Q-MI or emergency CABG developed. In the latest registries, the overall 30-day mortality and MI rate remain high - at 15 and 78%, respectively. In the OPTIMIST study, mortality even during PCI for stent thrombosis was 12% after 30 days and 17% after 6 months. The type of stent with which thrombosis developed does not affect short-term and long-term mortality. Unfavorable factors that worsen the 6-month prognosis in such patients include the lack of restoration of optimal blood flow, implantation of a second stent after initial stent thrombosis, three-vessel disease, and the presence of 2 or more overlapping stents.

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Treatment of stent thrombosis

Stent thrombosis is an emergency life-threatening situation. The procedure of choice is primary angioplasty, the purpose of which is mechanical recanalization of the thrombosed stent. Restoration of antegrade blood flow is achieved in 90% of cases on average, but the optimal result is observed only in 64% of cases. The optimal result was rarely achieved in case of LAD lesion, development of CGS, multivessel lesion, as well as in case of distal embolization of thrombotic masses. During the procedure, the use of IIb/IIIa receptor blockers is recommended, especially in high-risk patients: hypercoagulability, thrombocytosis, implantation of long stents, bifurcation lesion, small vessel diameter, presence of residual dissection, no-reflow phenomenon. In most cases, balloon angioplasty is sufficient, if possible with the use of thrombus aspiration devices. Repeated stenting should be performed only in case of significant residual dissection. According to the OPTIMIST registry, stent implantation is required in an average of 45% of cases. If PCI cannot be performed, TLT is used.

The overall rate of recurrent HT in the next 6 months is high, approximately 16.2% (with the rates of proven, probable, and possible HT being 6.7, 5.7, and 3.8%, respectively, according to the ARC classification). The average time to recurrent HT is 45 days (range, 2–175 days). The type of stent does not affect the rate of recurrent HT. In case of recurrent stent implantation during emergency PCI, the risk of recurrent HT increases 4-fold. Treatment of recurrent stent thrombosis is identical to primary treatment. In case of insufficient platelet aggregation while taking standard dual antiplatelet therapy (<50% of normal), the dose of clopidogrel should be increased to 150 mg/day.

Thus, the following conclusions can be made regarding stent thrombosis:

• The overall incidence of stent thrombosis is approximately 1.5%.
• Depending on the time of occurrence after PCI, acute, subacute, late and very late TS are distinguished.
• The most common are acute and subacute TS. After implantation of the LES, late TS occurs very rarely, they are more typical for DES.
• TS is manifested by a severe attack of angina, accompanied by ischemic dynamics on the ECG (usually with ST segment elevation).
• The method of choice for TS treatment is primary angioplasty, the purpose of which is mechanical recanalization of the thrombosed stent. If PCI cannot be performed, TLT is performed.
• In PCI for TS, a second stent is implanted only in cases of significant residual dissection. The use of IIb/IIIa receptor blockers is recommended during the procedure.
• The recurrence rate of TS is high (about 16%) and does not depend on the type of stent.
• The main measures for preventing stent thrombosis are ensuring full stent deployment and adherence to the timing of dual antiplatelet therapy.