[Optimal platelet inhibition after coronary stent implantation. Current status]

Abstract

Percutaneous coronary intervention (PTCA, PCI) is the most frequently used therapy for the treatment of stenoses or occlusions of coronary arteries. In Germany, six PCIs are performed for every coronary bypass surgery. Today, stents are implanted in over 80% of PCIs to improve the acute and long-term results. The most feared complication after stent implantation is the acutely occurring stent thrombosis, which usually leads to a myocardial infarction with its relatively high mortality. The introduction of platelet inhibition (acetylsalicylic acid [ASA] and ticlopidine/clopidogrel) decreased the rate of early (<or= 30 days) stent thromboses after implantation of bare-metal stents (BMS) to a clinically acceptable range of approximately 1%. Drug-eluting stents (DES) are a medical innovation, since they prevent or reduce the occurrence of clinically relevant restenoses and, therefore, the number and cost of repeat hospitalizations. After DES implantation, the rates of early stent thromboses are comparable to those of BMS, possibly even somewhat lower. Not much data is available regarding the incidence of late (> 30 days to 1 year) or very late (> 1 year) stent thromboses after BMS, but they do occur. Whereas a dual platelet inhibition of 4 weeks is sufficient after BMS, it must be performed longer after DES due to its prolonged period of endothelialization. In the randomized DES versus BMS studies, the rates of late and very late stent thromboses were increased with DES in the range of approximately 1 per thousand annually - but without affecting the mortality. DES may prevent myocardial infarctions by reducing restenoses, thus offsetting the possibly negative effects of late stent thrombosis. In patients with more extensive disease, previously sent to bypass surgery, the rate of late and very late stent thromboses is in the range of 0.6% per year. Since there is no control group from major randomized studies for these patients, more data have to be awaited.The optimal duration of dual platelet inhibition after DES is unknown, since no prospective, randomized trials have addressed this question. Based on the presently available data, clopidogrel must be given in addition to ASA for at least 6 months. Depending on the individual risk of stent thrombosis and the individual risk of bleeding, clopidogrel can be administered for 1 year or longer. Although a diminished effect of ASA and/or clopidogrel is known to be present in some patients, laboratory testing of platelet aggregation cannot be recommended for clinical decision- making at the present time due to missing standards and lack of pivotal studies. For clopidogrel, an increased platelet inhibition has been described with double dose (75 mg bid), but the clinical relevance is unknown. Whether new thienopyridine derivatives, like prasugrel, will also be superior to clopidogrel under "everyday" conditions has still to be shown. In patients with proven indication for chronic anticoagulation, the use of DES should be restricted or avoided. If a DES was nevertheless implanted, triple therapy (coumadin, ASA, and clopidogrel) is recommended--with an INR (International Normalized Ratio) target of 2.0, possibly adding a proton pump inhibitor. In case of nondeferrable surgery, dual platelet inhibition should be continued, if possible (like dental extractions), or perioperatively converted to a small-molecule glycoprotein IIb/IIIa inhibitor--under in-hospital survey. Further developments of next-generation DES with different drugs, modified release kinetics, specifically abluminal drug release or bioabsorbable polymers or absorbable stents are necessary, in order to reduce the duration of dual platelet inhibition to the range of BMS--but maintaining the well-established antiproliferative effects of DES.