Clopidogrel effect on platelet reactivity in patients with stent thrombosis: results of the CREST Study.

OBJECTIVES: We investigated whether patients who suffered subacute stent thrombosis (SAT) have higher post-treatment reactivity than those who do not encounter stent thrombosis. BACKGROUND: High post-treatment platelet reactivity has been reported after coronary stenting after clopidogrel therapy and may be an important factor in the occurrence of SAT. METHODS: We identified patients with SAT treated at two tertiary care centers over a 1.5-year period. Light transmittance aggregation induced by adenosine diphosphate (ADP) and arachidonic acid, total and activated glycoprotein (GP) IIb/IIIa after stimulation with ADP, and vasodilator-stimulated phosphoprotein phosphorylation levels to measure P2Y12 receptor inhibition were determined (n = 20) and compared with an age-matched group of patients without SAT (n = 100). High post-treatment platelet reactivity was defined as >75th percentile ADP-induced aggregation in the group without SAT. RESULTS: The SAT patients had higher mean platelet reactivity than those without SAT by all measurements (p < 0.05): 49 +/- 4% versus 33 +/- 2% for 5 micromol/l ADP-induced aggregation and 65 +/- 3% versus 51 +/- 2% for 20 micromol/l ADP-induced aggregation (p < 0.001), 69 +/- 5% versus 46 +/- 9% for P2Y12 reactivity ratio (p = 0.03), and 138 +/- 19 mean fluorescence intensity (MFI) versus 42 +/- 4 MFI for stimulated GP IIb/IIIa expression (p < 0.001). Of patients with SAT, 60% had high platelet reactivity. CONCLUSIONS: High post-treatment platelet reactivity and incomplete P2Y12 receptor inhibition are risk factors for SAT. Measures to uniformly determine platelet reactivity after coronary stenting and treatment strategies to improve P2Y12 receptor inhibition in patients with high post-treatment platelet reactivity should be further investigated.

The difference between clopidogrel responsiveness and posttreatment platelet reactivity.

BACKGROUND: Aggregation is the most common measure of platelet reactivity. The relative inhibition of platelet aggregation between pretreatment and posttreatment is the most common estimate of clopidogrel responsiveness. However, patients responsive to clopidogrel may remain with highly reactive platelets and thus have increased thrombotic risk. METHODS: Platelet reactivity was determined by ADP-induced aggregation (%) in 62 patients undergoing elective coronary stenting at pretreatment and 5 days postprocedure. All patients were on aspirin (325 mg) and received 300 mg of clopidogrel immediately poststenting and 75 mg qd. Pretreatment reactivity was divided into tertiles. Based on clopidogrel drug responsiveness, nonresponders were defined as <10% relative inhibition of pretreatment aggregation, semiresponders as 10-30%, and responders as >30%. We determined the relation between clopidogrel responsiveness and platelet reactivity. RESULTS: Pretreatment reactivity tertiles by 5 microM ADP were: low (47+/-9%), moderate (64+/-4%), and high (78+/-6%). Eight patients were nonresponders, 18 were semiresponders, and 36 were responders. Clopidogrel responsiveness directly correlated with pretreatment reactivity, 86% of responders had moderate or high pretreatment reactivity, whereas 75% of nonresponders had low pretreatment reactivity. Despite being more responsive, 16% of patients with high pretreatment reactivity and 17% with moderate pretreatment reactivity remained with moderate posttreatment reactivity. CONCLUSION: Measuring clopidogrel responsiveness may overestimate the risk of stent thrombosis in nonresponders with low pretreatment reactivity and underestimate risk in those responders who remain with high posttreatment platelet reactivity. Posttreatment platelet reactivity is a better measure of thrombotic risk than responsiveness to clopidogrel.

Failure of clopidogrel to reduce platelet reactivity and activation following standard dosing in elective stenting: implications for thrombotic events and restenosis.

There is no information on long-term platelet reactivity and activation following elective stenting in patients treated with clopidogrel and aspirin. We measured platelet reactivity and activation at baseline and at 2 h, 24 h, 5 days and 30 days following coronary stenting (n = 94). Patients were treated with the standard aspirin (325 mg) and clopidogrel regimen (300 mg load/75 mg qd). Reactivity was measured by aggregation (5 and 20 microM ADP) and activation was determined by the expression of total and active GP IIb/IIIa. Reactivity and activation were defined as heightened when post-stent aggregation and receptor expression exceeded baseline levels, respectively. Prolonged heightened platelet reactivity was detected by both 5 and 20 microM ADP aggregation. Using 20 microM ADP aggregation, heightened reactivity occurred in 55% of patients at 2 h, 26% at 24 h, 21% at 5 days, and 15% at 30 days post-stenting. A high frequency of heightened platelet activation was detected by both total and active GP IIb/IIIa expression. Using expression of the active GP IIb/IIIa receptor as the marker, activation was greater than baseline in 27% of patients at 2 h, 20% at 24 h, 30% at 5 days, and 22% at 30 days post-stenting. This is the first report demonstrating that a significant percentage of patients receiving standard clopidogrel and aspirin therapy for coronary stenting will have post-drug platelet reactivity and activation above baseline that persists for 30 days after the procedure. These finding suggest insufficient platelet inhibition. The clinical importance of these findings should be further investigated to establish the potential link between insufficient platelet inhibition, stent thrombosis, and restenosis.

The role of platelet receptors and adhesion molecules in coronary artery disease.

Platelets play a significant role in coronary artery disease through interactions with each other and with other cell types. These interactions are mediated by certain receptors on the surface of platelets and other cells which can lead to intra-coronary thrombus formation and occlusion that may result in acute coronary syndromes. The important roles of the currently available anti-platelet therapies have been well established in many clinical outcome trials in cardiovascular patients. An understanding of these different interactions provides the clinician with a background that supports the clinical importance of currently available anti-platelet therapies. Moreover, knowledge of the mechanisms of cellular crosstalk will lead to important advances in the development of better antithrombotic therapies.