Background: Dual antiplatelet therapy (DAPT) became the mainstay of management of acute coronary syndrome (ACS), with clopidogrel therapy providing clear benefits in preventing stent thrombosis. While newer antiplatelet agents have become available, clopidogrel is still widely used due to its low cost and efficacy. Clopidogrel resistance is a laboratory phenomenon in which there is no adequate inhibition of platelet reactivity despite clopidogrel treatment. Treatment failure is a clinical phenomenon, namely, the occurrence of a thrombotic/ischemic event during clopidogrel therapy. Platelet reactivity associated with and the clinical significance of clopidogrel failure is unknown.
Methods: We describe the clinical features of consecutive patients admitted due to ACS, while on chronic DAPT including clopidogrel therapy. All patients underwent coronary angiography. ADP- and arachidonic acid induced platelet aggregation (PA) was determined on admission (before administering any new anti-platelet therapy).
Results: Nineteen consecutive patients were admitted with a diagnosis of ACS while on chronic clopidogrel therapy (66±11 yo, 84% male). ST-elevation myocardial infarction was diagnosed in 68.4% of the patients and 31.6% were diagnosed as non ST-elevation MI. Although stent thrombosis was demonstrated in as much as 26% of the patients, in 74% the index ACS related culprit lesion did not involve a previously implanted stent. The average ADP induced aggregation was 60±18%. Platelet suboptimal response to clopidogrel was found in most patients (63%). Aspirin resistance was found in 68% of the patients, and dual anti-platelet resistance in 42% of the patients. Interestingly, patients in whom the index ACS represented stent thrombosis versus those in whom the index event involved de novo lesion did not differ in their platelet reactivity.
Conclusions: ACS while on chronic clopidogrel therapy ("clopidogrel failure") is associated with high incidence of both clopidogrel and dual antiplatelet suboptimal response and associated with relatively high risk for stent thrombosis.
