Author + information
- Received December 20, 2010
- Revision received April 14, 2011
- Accepted April 19, 2011
- Published online July 26, 2011.
- Laurent Bonello, MD⁎,†,⁎ (, )
- Michel Pansieri, MD‡,
- Julien Mancini, MD§∥,
- Roland Bonello, MD¶,
- Luc Maillard, MD#,
- Pierre Barnay, MD‡,
- Philippe Rossi, MD⁎⁎,
- Omar Ait-Mokhtar, MD⁎,
- Bernard Jouve, MD††,
- Frederic Collet, MD¶,
- Jean Pascal Peyre, MD‡‡,
- Olivier Wittenberg, MD§§,
- Axel de Labriolle, MD∥∥,
- Elise Camilleri, MD¶¶,
- Edouard Cheneau, MD##,
- Elma Cabassome, MD⁎,
- Françoise Dignat-George, PhD†,⁎⁎⁎,
- Laurence Camoin-Jau, PhD†,⁎⁎⁎ and
- Franck Paganelli, MD⁎
- ↵⁎Reprint requests and correspondence:
Dr. Laurent Bonello, Department of Cardiology, Hôpital Universitaire Nord, Chemin des Bourrely, 13015 Marseille, France
Objectives The aim of this study was to investigate the relationship between platelet reactivity (PR) after a loading dose (LD) of prasugrel and thrombotic events.
Background Post-treatment PR has been shown to be strongly associated with the occurrence of major adverse cardiac events (MACE) after percutaneous coronary intervention (PCI) in the clopidogrel era. Prasugrel is a new P2Y12–adenosine diphosphate receptor with a higher potency on PR.
Methods A prospective multicenter study included patients who underwent successful PCI for acute coronary syndromes and received prasugrel therapy. Vasodilator-stimulated phosphoprotein (VASP) index was measured after the prasugrel LD. High on-treatment PR was defined as a VASP index ≥50%. MACE included cardiovascular death, myocardial infarction, and definite stent thrombosis at 1 month.
Results Three hundred one patients were enrolled. The mean VASP index after 60 mg of prasugrel was 34.3 ± 23.1%. High on-treatment PR was observed in 76 patients (25.2%). Patients experiencing thrombotic events after PCI had significantly higher VASP indexes compared with those free of events (64.4 ± 14.4% vs. 33.4 ± 22.7%; range: 51% to 64% and 5% to 47.6%, respectively; p = 0.001). Kaplan-Meier analysis comparing good responders and patients with high on-treatment PR demonstrated a significantly higher rate of MACE in patients with suboptimal PR inhibition (log-rank p < 0.001). Receiver-operating characteristic curve analysis found a cutoff value of 53.5% of the VASP index to predict thrombotic events at 1 month (r = 0.86, p < 0.001). Patients with minor or major Thrombolysis In Myocardial Infarction unrelated to coronary artery bypass grafting bleeding and those without had similar VASP indexes (30 ± 17.8% vs. 34.3 ± 23%, p = 0.70).
Conclusions Despite the use of prasugrel, a significant number of patients undergoing PCI in the setting of acute coronary syndromes do not achieve optimal PR inhibition. Such patients have a higher risk for MACE after PCI.
- antiplatelet therapy
- high on-treatment platelet reactivity
- platelet monitoring
- P2Y12-ADP receptor antagonist
- stent thrombosis
- VASP index
The addition of clopidogrel to aspirin in patients undergoing percutaneous coronary intervention (PCI) for acute coronary syndromes (ACS) has enabled a dramatic decrease in the rate of thrombotic events (1). However, clopidogrel has 3 main limitations: a slow onset of action, mild potency, and large interindividual variability in response (2,3). Of importance, several studies have highlighted a link between high on-treatment platelet reactivity (HTPR), or suboptimal platelet reactivity (PR) inhibition, as measured by platelet assays after a clopidogrel loading dose (LD) and the occurrence of thrombotic events after PCI (3,4). The vasodilator-stimulated phosphoprotein (VASP) index is the most specific platelet assay to assess PR inhibition related to P2Y12–adenosine diphosphate (ADP) receptor antagonists. A recent consensus has been published, on the basis of receiver-operating characteristic (ROC) curve analysis, regarding the predictive value of various platelets assays to predict major adverse cardiac events (MACE) after PCI. In this consensus report, HTPR was defined as a VASP index ≥50% (3). This cutoff value exhibited very high negative predictive value for thrombotic events in several trials and has therefore been used to tailor therapy to improve clinical outcomes in patients undergoing PCI (5,6).
Prasugrel is a third-generation thienopyridine that has demonstrated faster and more potent P2Y12-ADP receptor inhibition than clopidogrel (7). Like clopidogrel, prasugrel is a prodrug that requires bioactivation steps, including biotransformation by hepatic cytochromes into actives metabolites. In TRITON–TIMI 38 (Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition With Prasugrel–Thrombolysis In Myocardial Infarction 38), prasugrel therapy resulted in a significant reduction in MACE after PCI compared with clopidogrel in patients with ACS (8). Its benefit, within the first 30 days, was related to a reduction in recurrent thrombotic events, including early stent thrombosis. This benefit is related to the favorable pharmacodynamic profile of prasugrel compared with clopidogrel, as these 2 drugs share similar active metabolites (9). Interestingly, in a recently published substudy of TRITON–TIMI 38, the investigators observed a relatively high rate of HTPR, as defined using the consensus definition, in patients receiving prasugrel therapy (10). However, to date, a potential link between PR inhibition and recurrent thrombotic events after PCI has not been evaluated in patients receiving prasugrel therapy. In the present study, we aimed to investigate the relationship between PR inhibition and the occurrence of MACE in patients undergoing successful PCI for ACS and receiving prasugrel.
A prospective multicenter study was performed. Patients presenting with ACS and undergoing successful PCI who received prasugrel and gave informed consent to participate in the study were eligible. Patients were enrolled in the study between February and September 2010. The protocol was approved by each of the local ethics committees and was in accordance with the Declaration of Helsinki.
Exclusion criteria were failed PCI, cardiac arrest, contraindications to antiplatelet therapy, a platelet count <100 g/l, history of bleeding diathesis, concurrent severe illness with expected survival <1 month, surgery within 1 month or scheduled in the following year, age over 75 years, warfarin or other oral anticoagulant therapy, weight <60 kg, history of stroke, noncompliance with therapy, or an inadequate prasugrel LD. Five patients were excluded from the study because they did receive concomitant anticoagulant therapy (warfarin) after PCI.
Blood samples for VASP index analysis were drawn by atraumatic venipuncture of the antecubital vein at least 6 h and within 12 h after prasugrel LD. The initial blood drawn was discarded to avoid measuring platelet activation induced by needle puncture; blood was collected into a Vacutainer (Becton, Dickinson and Company, Franklin Lakes, New Jersey) containing 3.8% trisodium citrate and filled to capacity. The Vacutainer was inverted 3 to 5 times for gentle mixing and sent immediately to the hemostasis laboratory. VASP index phosphorylation analysis was performed within 24 h of blood collection by an experienced investigator using Platelet VASP kits (Diagnostica Stago, Asnières, France) (4,5). Briefly, a citrated blood sample was incubated with prostaglandin E1 (PGE1) or with PGE1 and ADP 10 μmol/l for 10 min and fixed with paraformaldehyde, after which the platelets were permeabilized with a nonionic detergent. Analyses were performed on an EPICS XL-MCL flow cytometer (Beckman Coultronics, Margency, France), the platelet population was identified from its forward and side scatter distribution, and 10,000 platelets were gated. VASP index was calculated from the mean fluorescence intensity (MFI) of samples incubated with PGE1 or PGE1 and ADP according to the formula: VASP = [(MFIPGE1 − MFIPGE1_ADP)/MFIPGE1] × 100. HTPR was defined as a VASP index ≥ 50% according to the consensus definition (3).
PCI was performed according to international guidelines, using a standard technique through the radial or femoral route. Successful stent implantation was achieved in all patients. Either a drug-eluting or a bare-metal stent was used according to French Society of Cardiology guidelines. The sheath was removed immediately at the end of the procedure in all cases. Routine care before and after the procedure was undertaken for all patients, including pre-treatment with prasugrel (60-mg LD) at least 6 h before VASP index measurement, followed by 10 mg/day for at least 1 year. In addition, all patients received aspirin 75 mg/day for at least 1 year, with an LD of 250 to 500 mg administered 12 h before stent implantation or at the time of PCI in patients with ST-segment elevation myocardial infarction. Compliance with aspirin and prasugrel was assessed by nurses during hospital stay and by medical contact at 1 month. Anticoagulation with unfractionated heparin was begun in the intensive care unit before PCI. During PCI, patients were anticoagulated with unfractionated heparin (a bolus of 40 U/kg and additional heparin to achieve an activated clotting time of 250 to 300 s). Anticoagulation was stopped at the end of the procedure in all patients. Glycoprotein IIb/IIIa inhibitors were administered at the discretion of the interventional cardiologist and were used according to guidelines. Failed PCI was defined as a failure to obtain a residual stenosis <30% after stent implantation and/or post-PCI TIMI flow grade <3.
The primary endpoint was a composite of cardiovascular (CV) death, nonfatal myocardial infarction, and stent thrombosis at 1 month. CV death was considered as any death with a demonstrable CV cause or any death that was not clearly attributable to a non-CV cause. Stent thrombosis was defined according to the Academic Research Consortium definition (11). Nonfatal myocardial infarction was defined as recurrent ischemic symptoms (>20 min) and/or electrocardiographic changes after PCI with an increase ≥20% of troponin measured after the recurrent event, with at least 1 value above the 99th percentile of the reference range (12).
The secondary endpoint was the rate of major and minor TIMI bleeding unrelated to coronary artery bypass grafting (CABG) at 1 month.
All statistical analyses were performed using SPSS version 17.0 (SPSS, Inc., Chicago, Illinois). Continuous variables are expressed as mean ± SD or as median (range or interquartile range). Categorical variables are expressed as frequencies and percents. Standard 2-sided tests were used to compare continuous characteristics (Student t or Mann-Whitney U tests) or categorical characteristics (chi-square or Fisher exact tests) among patient groups. Mann-Whitney U and Fisher exact tests were used in the univariate analysis studying factors associated with thrombotic events at 1 month. The sensitivity and specificity of the VASP index to predict thrombotic events were calculated at different thresholds in a ROC curve analysis. The “optimal” cutoff value was defined by the highest Youden index value (sensitivity + specificity − 1). A complementary analysis compared the time to thrombotic events between HTPR and good responder groups using the Kaplan-Meier method. Survival curves were compared using the log-rank test. A p value <0.05 was considered significant.
Baseline demographic, clinical, angiographic, and biological characteristics are summarized in Table 1. A total of 301 patients were enrolled. The majority of the study population were men (n = 267 [88.7%]), with a mean age of 58.1 ± 10.4 years. The prevalence of diabetes mellitus was 23.3%. All patients had ACS at the time of inclusion; 42.5% of the patients were included after ST-segment elevation myocardial infarction.
The mean VASP index after a 60-mg LD of prasugrel was 34.3 ± 23.1% (range 5% to 76.6%). We observed large interindividual variability in prasugrel responsiveness, with VASP indexes ranging from 1% to 82.8% (Fig. 1). Although the vast majority of patients (74.8%) were considered to have optimal PR inhibition, using a 50% cutoff value to define HTPR, 76 patients (25.2%) were considered to have insufficient PR inhibition after prasugrel LD. In addition, 101 patients (33.6%) had VASP indexes <20% after prasugrel LD.
The 30-day outcomes are displayed in Table 2. Three patients were lost to follow-up. No patient underwent CABG during the follow-up period. The primary endpoint was met in 8 patients within the first month after PCI. There was 1 CV death related to a definite stent thrombosis, 3 nonfatal definite stent thromboses, and 4 nonfatal myocardial infarctions. The secondary endpoint was met in 5 patients, with 2 major and 3 minor non-CABG-related TIMI bleeding events. Major bleeds were 1 puncture site hematoma and 1 gastrointestinal bleed, both requiring blood transfusion (Table 2).
Relationship between PR and CV events at 1 month
The mean VASP index was significantly higher in patients experiencing recurrent thrombotic events compared with those free of events at 1 month (64.4 ± 14.4% vs. 33.4 ± 22.7%, p = 0.001; interquartile range: 55.5% to 76.2% and 14% to 47.6%, respectively). When comparing patients with and without MACE at 1 month, the 2 factors significantly associated with thrombotic events were the VASP index (p = 0.001) and hypercholesterolemia (p = 0.032) (Table 3).
No difference could be observed between patients with a minor or major non-CABG-related TIMI bleeding at 1 month and those without regarding the VASP index (30 ± 17.8% vs. 34.3 ± 23.1%, p = 0.70).
ROC analysis was performed to evaluate the predictive value of the VASP index for thrombotic events. The area under the curve was 0.86. The optimal cutoff value for the VASP index to predict CV events was 53.5%, with sensitivity of 87.5% and specificity of 76.5%. For this cutoff value, the positive and negative predictive values were 10.4% and 99.6%, respectively. The 50% cutoff value mentioned in the consensus document had sensitivity of 87.5% and specificity of 79.5%. The positive and negative predictive values of this cutoff value were 9.2% and 99.6%, respectively (Fig. 2).
Comparison between good responders and patients with HTPR
We compared the good responder and HTPR groups to evaluate the relationship between VASP index and in-hospital thrombotic events or bleeding (Table 4). There were no differences between these 2 groups regarding demographic, clinical, angiographic, or biological data, except for sex (p = 0.007).
Kaplan-Meier analysis demonstrates that patients with HTPR had significantly worse 1-month outcomes compared with good responders (9.2% vs. 0.4%, log-rank p < 0.001) (Fig. 3).
All but 1 patient with non-CABG-related TIMI major and minor bleeding events had VASP indexes <50%. However, there was no difference between the HTPR and good responder groups regarding TIMI bleeding events (p = 1.00).
The present study demonstrates that a significant number of patients receiving prasugrel for ACS and treated by PCI have insufficient PR inhibition as assessed by the VASP index. Of importance, these patients with HTPR after prasugrel LD had a significantly higher rate of recurrent thrombotic events during the 1-month follow-up period after PCI.
Prasugrel is a new-generation thienopyridine with a faster onset of action and a higher potency, which translate into improved outcomes compared with clopidogrel in patients with ACS treated with PCI (7,8). In the present study, we observed that 25% of patients with ACS have HTPR after a prasugrel LD, which is similar to that observed in a substudy of TRITON–TIMI 38. This number is lower than that observed after clopidogrel LD, which was about 50% using the same platelet assay (5,6). Furthermore, in the present study, we observed that patients with HTPR after prasugrel LD experienced a higher rate of thrombotic events than those with adequate response to the drug. In addition, in the present study, ROC analysis observed a similar cutoff value of the VASP index for thrombotic events (53.5%) compared with the consensus definition. Consistent with previous reports in the clopidogrel era, this cutoff value had a very high negative predictive value for thrombotic events with prasugrel therapy (3,13).This result is also consistent with the fact that prasugrel and clopidogrel share similar properties and in particular similar active metabolites. The main difference between the 2 drugs is in fact related to the efficiency of their biotransformation pathways (9).
Prasugrel therapy was associated in TRITON–TIMI 38 with a higher rate of bleeding events, which may be related to its higher potency. Although a large number of patients had very low PR after prasugrel LD in the present study, the rate of TIMI bleeding events was low, and no relationship could be found between PR and bleeding (14). However, despite the lack of association between PR and bleeding events in the present study, previous trials using clopidogrel have suggested that there is an association between excessive PR inhibition and bleeding complications. These findings suggest that there may a therapeutic window of P2Y12-ADP receptor antagonists to reach to prevent thrombotic events and not increase the bleeding risk (3).
Although in the present study, the VASP index was used to monitor PR inhibition, other platelet assays, such as the Multiplate analyzer (Verum Diagnostica GmbH, Munich, Germany) and the VerifyNow P2Y12 (Accumetrics, Inc., San Diego, California), have been shown to be of similar predictive value (3).
In the present study, no baseline demographic or clinical characteristic was predictive of HTPR but sex. This result illustrates the higher potency of the drug over clopidogrel, for which body mass index, diabetes, clinical setting, and age were independent predictors of HTPR together with cytochrome 2C19 polymorphism (15). Consistent with a potential impact of sex on PR, Hobson et al. (16) suggested that women were more likely to have a higher clotting tendency with lower response to both aspirin and clopidogrel. Given the small number of women included in the present study, this result requires confirmation in future trials.
Given the results of the present study, although significantly reducing thrombotic events after PCI because of its superior potency, prasugrel therapy may require PR monitoring to enable optimal PR inhibition to be achieved, which may lead to improved outcomes in all patients. We have previously demonstrated that adjusting the LD of clopidogrel to achieve a VASP index <50% in patients with HTPR improved clinical outcomes by reducing the rate of early stent thrombosis (5,6). The GRAVITAS (Gauging Responsiveness With a VerifyNow Assay: Impact on Thrombosis and Safety) study aimed to confirm these preliminary findings by showing that increased clopidogrel doses in patients with HTPR could be of clinical benefit. The results of this trial were negative. However, the dose adjustment strategy was notably insufficient, and because the majority of patients were at low risk for thrombotic events, the study was underpowered to test the hypothesis (17). Thus, the concept of an optimal level of PR inhibition to further improve clinical outcomes remains to be confirmed. Such individualized therapy could be of critical interest if additional studies support an association between bleeding events and PR inhibition in the prasugrel era. In fact, the therapeutic window could therefore be used to balance between the thrombotic and bleeding risk.
Limitations of the present study included the relatively small sample size and rate of thrombotic events. In fact, because the number of event is small, this finding should be considered as hypothesis generating and warrants a larger trial to confirm the relationship between PR inhibition under prasugrel therapy and thrombotic events. However, the results are supported by the large amount of published data supporting this link in the clopidogrel era.
Despite the use of a prasugrel LD, a significant number of patients with ACS undergoing PCI do not achieve optimal PR inhibition. Such patients have a higher risk for MACE after PCI. This result suggests that PR monitoring to tailor P2Y12-ADP receptor antagonist therapy may be of interest with prasugrel use to further improve patient outcomes. Larger trials are needed to confirm these hypotheses.
The authors are grateful to Soraya Moulay for her help in study and data management and to Probal Roy for careful reviewing of the manuscript.
This work was supported by a research grant from Eli Lilly and by Assistance Publique–Hopitaux de Marseille. Dr. Bonello has received a research grant from Eli Lilly and AP-HM. All other authors have reported that they have no relationships to disclose.
- Abbreviations and Acronyms
- acute coronary syndromes
- adenosine diphosphate
- coronary artery bypass grafting
- high on-treatment platelet reactivity
- loading dose
- major adverse cardiac event(s)
- mean fluorescence intensity
- percutaneous coronary intervention
- prostaglandin E1
- platelet reactivity
- receiver-operating characteristic
- Thrombolysis In Myocardial Infarction
- vasodilator-stimulated phosphoprotein
- Received December 20, 2010.
- Revision received April 14, 2011.
- Accepted April 19, 2011.
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