To assess the prognostic value of clopidogrel in patients with an acute coronary syndrome (ACS) without persistent ST-segment elevation.
We studied clopidogrel response prospectively in 49 patients treated with a loading dose of 300 mg clopidogrel followed by a maintenance dose of 75 mg/day. VASP index was calculated from the median fluorescence intensity (MFI) of samples incubated with prostaglandin E1 (PGE1) and adenosine diphosphate according to the formula [(MFI(PGE1)–MFI(PGE1–ADP))/MFI(PGE1)] × 100, and was determined at baseline and at days 1 and 4 after starting clopidogrel. We correlated VASP index with occurrence of recurrent cardiovascular events over six-month follow-up.
There was a significant stepwise decrease in VASP index from baseline (86 ± 6 % ) to day 1 (71 ± 13 % ) and day 4 (61 ± 16 % ; p < 0.001) with marked interindividual variability. Patients who experienced recurrent cardiovascular events displayed a higher VASP index compared with those free of events (76 ± 3 % versus 59 ± 16 % , p = 0.006). Five of six recurrent events occurred in patients in the upper quartile of VASP index measured at day 4. The best cut-off of platelet reactivity index of VASP to predict high-risk ACS patients was at 70 % .
Assessment of VASP index in ACS patients identifies low responders to clopidogrel who are at increased risk of recurrent cardiovascular events.