Author + information
- Received May 11, 2010
- Revision received September 8, 2010
- Accepted September 28, 2010
- Published online January 25, 2011.
- Olivier Morel, MD, PhD⁎,†,⁎ (, )
- Soraya El Ghannudi, MD⁎,
- Laurence Jesel, MD⁎,
- Bogdan Radulescu, MD⁎,
- Nicolas Meyer, MD, PhD‡,
- Marie-Louise Wiesel, MD§,
- Sophie Caillard, MD, PhD∥,
- Umberto Campia, MD¶,
- Bruno Moulin, MD, PhD∥,
- Christian Gachet, MD, PhD§ and
- Patrick Ohlmann, MD, PhD⁎
- ↵⁎Reprint requests and correspondence:
Prof. Olivier Morel, Pôle d'activité médico-chirurgicale Cardiovasculaire, Nouvel Hôpital Civil, Strasbourg, BP 426-67091, France
Objectives We sought to determine whether low platelet response to the P2Y12 receptor antagonist clopidogrel as assessed by vasodilator-stimulated phosphoprotein flow cytometry test (VASP-FCT) differentially affects outcomes in patients with or without chronic kidney disease (CKD) undergoing percutaneous coronary intervention (PCI).
Background Although both CKD and impaired platelet responsiveness to clopidogrel are strong predictors of unfavorable outcome after PCI, the impact of their association is unknown. The platelet VASP-FCT assay is specific for the P2Y12 ADP receptor pathway. In this test, platelet activation is expressed as the platelet reactivity index (PRI).
Methods Four-hundred forty unselected patients (CKD: 126, estimated glomerular filtration rate [eGFR] <60 ml/min/1.73 m2), no-CKD: 314 eGFR >60 ml/min/1.73 m2) undergoing urgent (n = 336) or planned (n = 104) PCI were prospectively enrolled. In each subgroup, patients were classified as low-responders (LR: PRI ≥61%) or responders (R: PRI <61%) to clopidogrel.
Results At a mean follow-up of 9 ± 2 months, all-cause mortality, cardiac death, and possible stent thrombosis were higher in CKD than in no-CKD patients. Within the CKD group, the LR status was associated with higher rates of all-cause mortality (25.5% vs. 2.8%, p < 0.001), cardiac death (23.5% vs. 2.8%, p < 0.001), all stent thrombosis (19.6% vs. 2.7%, p = 0.003), and MACE (33.3% vs. 12.3%, p = 0.007). Conversely, in no-CKD patients, the LR status did not affect outcomes. Multivariate analysis identified Killip class ≥3, drug-eluting stent implantation, and the interaction between LR and CKD (hazard ratio: 11.96, 95% confidence interval: 1.22 to 116.82; p = 0.033) as independent predictors of cardiac death.
Conclusions In CKD patients, the presence of low platelet response to clopidogrel is associated with worse outcomes after PCI.
The combined pharmacological inhibition of the P2Y12 receptor by thienopyridines and of the cyclooxygenase pathway by aspirin is currently considered the reference antiplatelet strategy to minimize the risk of thrombotic complications following percutaneous coronary interventions (PCI) (1,2). However, significant variability exists in the rate of platelet inhibition with this therapy, and an impaired platelet responsiveness to clopidogrel may be associated with worse cardiovascular outcomes in patients treated by PCI (3–5).
Patients with chronic kidney disease (CKD) present with accelerated atherosclerosis and higher cardiovascular morbidity and mortality (6–11). Furthermore, CKD is associated with adverse outcome following PCI (12–14), likely related to endothelial dysfunction, inflammation, and platelet activation. However, whether an impaired platelet inhibition to clopidogrel is an independent predictor of cardiovascular outcomes in patients with CKD remains unknown. The present study was therefore designed to test the hypothesis that low platelet responsiveness to clopidogrel, as assessed by vasodilator stimulated phosphoprotein (VASP) phosphorylation, independently contributes to adverse cardiovascular events after PCI in patients with CKD.
This study enrolled consecutive patients undergoing PCI for an acute coronary syndrome or stable coronary artery disease in our institution between September 2007 and December 2008. The study was performed in accordance with the Declaration of Helsinki. The protocol was approved by the institutional ethics committee, and informed written consent was obtained from all patients.
Renal function staging
Baseline serum creatinine levels were assessed at admission in all patients. The estimated glomerular filtration rate (eGFR) was calculated using the abbreviated MDRD (Modification of Diet in Renal Disease) formula according to Levey et al. (15). Patients were divided into 4 subgroups according to their eGFR levels: ≥90 ml/min/1.73 m2; ≥60 and <89 ml/min/1.73 m2; ≥30 and <59 ml/min/1.73 m2; and <30 ml/min/1.73 m2). Patients with an eGFR <60 ml/min/1.73 m2 were assigned to the CKD group, whereas those with an eGFR ≥60 ml/min/1.73 m2 were assigned to the no-CKD group.
Whole blood samples were collected by venipuncture at least 6 h after a loading dose (300 or 600 mg) of clopidogrel. Blood was collected into Vacutainer tubes containing 0.129 M sodium citrate (BD Vacutainer, Becton Dickinson, Sparks, Maryland) and immediately sent to the hemostasis laboratory (EFS-Alsace).
Analysis of VASP phosphorylation by flow cytometry
Post-PCI platelet VASP phosphorylation was assessed in all patients using a standardized flow cytometric assay (Platelet VASP, Biocytex, Diagnostica Stago, Asnières, France) as previously described (16). Levels of VASP phosphorylation reflect P2Y12 inhibition and are expressed as the platelet reactivity index (PRI), calculated from the median fluorescence intensity (MFI) of samples incubated with prostaglandin E1 (PGE1) or PGE1 and ADP according to the formula: PRI = [(MFIPGE1 − MFIPGE1+ADP)/MFIPGE1] × 100 (16). The advantages of the VASP assay are its selectivity for the P2Y12 pathway, its insensitivity toward glycoprotein IIb/IIIa inhibitors, the stability of the results for more than 24 h after blood sampling, and the interpretability of single measurements (17). In unselected patients undergoing PCI, we recently found that the optimal cutoff value for PRI to predict cardiovascular outcome following PCI was 61% using a receiver-operating characteristic curve analysis based on the maximal value of the Youden index (18). Therefore, patients were considered to have a low platelet response to clopidogrel (low responders) if their PRI was ≥61%, and a normal response to clopidogrel (responders) if their PRI was <61%.
Clinical end points
The primary end points of the study were all-cause mortality, cardiovascular mortality (defined as any death with demonstrable cardiovascular cause or any death that was not clearly attributable to a noncardiovascular cause), ST-segment elevation myocardial infarction (STEMI, defined as a new or presumably new ST-segment elevation in 2 consecutive leads associated with an increase in biochemical markers of myocardial necrosis), and non–ST-segment elevation myocardial infarction (NSTEMI, defined as the occurrence of ischemic symptoms, ST-segment depression and/or T-wave abnormalities, and an increase of biochemical markers of myocardial necrosis). Post-PCI troponin (Tn) elevations were not considered as indicating a recurrent myocardial infarction. Secondary end points included: definite/probable stent thrombosis, possible stent thrombosis, all stent thrombosis, and major adverse cardiac events (MACE), defined as the composite of all-cause mortality, nonfatal myocardial infarction, or target lesion revascularization. The diagnosis of stent thrombosis was defined according to the Academic Research Consortium criteria as follows: definite = acute coronary syndrome and angiographic or pathologic evidence of stent thrombosis; probable = unexplained death within 30 days or target vessel infarction without angiographic information; and possible = unexplained death after 30 days of stent placement. Follow-up data were obtained through a questionnaire sent to the patients' cardiologists or referring physicians and collected by phone. End points were adjudicated by 2 independent physicians who were blind to PRI values.
Continuous variables are expressed as median (interquartile range); categorical variables are expressed as frequencies and percentages. Continuous variables between 2 groups were compared by Student t test or by Mann-Whitney test as appropriate. Fisher exact test was used for comparison of categorical variables. Continuous variables were analyzed for normal distribution using the Shapiro-Wilk test. Time to event was defined as the time from PCI to the date of event, with patients censored at death, loss to follow-up, or end of the study (June 30, 2009). Kaplan-Meier analyses were used to construct survival plots of time to death after PCI and compared using log-rank test. Multivariate analysis of survival rates was done using Cox models. Variables with p < 0.05 in univariate analysis were entered into a stepwise ascending multivariate analysis. To evaluate a differential effect of low response to clopidogrel in the presence or in the absence of CKD, an interaction term between these 2 terms was introduced in the model, in addition to the 2 main effects of these variables. The results of the Cox regression are presented as hazard ratios (HR), their 95% confidence intervals (CIs), and p values. A p value <0.05 was considered statistically significant. Statistical analysis was performed using SPSS version 13.0 software (SPSS Inc., Chicago, Illinois).
Baseline characteristics and biological response to clopidogrel
A total of 440 consecutive patients treated by planned (n = 104, 23.6%) or urgent PCI (n = 336, 76.3%) were enrolled in this study. Of them, 314 had eGFR ≥60 ml/min/1.73 m2 (no-CKD group), and 126 had eGFR >60 ml/min/1.73 m2 (CKD group). Baseline demographics and clinical, biological, and angiographic characteristics of the 2 groups are described in Tables 1, 2, and 3.⇓⇓ The majority (n = 104, 82.5%) of CKD patients had an eGFR between 30 and 59 ml/min/1.73 m2 (stage III CKD according to the National Kidney Foundation Kidney Disease Outcome Quality Initiative), whereas the remaining CKD patients (n = 22, 17.4%) had an eGFR between 15 and 29 ml/min/1.73 m2 (stage IV CKD). As expected, diabetes mellitus was more prevalent among CKD patients than in patients with normal renal function (46.8% vs. 33.8%, respectively; p = 0.012). Among all patients, 261 had normal platelet response to clopidogrel (188 in the no-CKD group and 73 in the CKD group), and 179 had low platelet response (126 in the no-CKD group and 53 in the CKD group).
The time elapsed between the administration of the clopidogrel loading dose and VASP measurement was <12 h in 66 patients (15%), between 12 and 24 h in 165 patients (37.5%), between 24 and 48 h in 66 patients (15%), between 48 and 72 h in 60 patients (13.6%), and >72 h in 83 patients (18.8%). The delay between clopidogrel loading dose and VASP assay was similar between the low responder and responder groups, and between the CKD and no-CKD groups.
The median value of PRI (%) was not significantly different between the CKD and the no-CKD groups (55.8 [25th to 75th percentile: 40.3 to 70.2] vs. 55.7 [25th to 75th percentile: 35.5 to 70.4]; p = 0.534). In each of these 2 groups, patients were divided into 2 separate subgroups according to a PRI cutoff value of 61%. The proportion of low responder patients was similar between the CKD and no-CKD groups (42.0% vs. 40.1%, respectively; p = 0.748). Likewise, the cumulative clopidogrel dose (total dose received prior to testing) did not differ. The proportion of stage IV patients was not statistically different between the responder and low responder subgroups (13.7% vs. 22.6%, respectively; p = 0.237).
Impact of CKD on cardiovascular outcomes
Clinical outcomes were available in 433 of 440 patients (98.4%), with a mean follow-up of 9 ± 2 months (range 6 to 14 months). At follow-up, the rate of dual antiplatelet therapy was lower in CKD patients compared with those with normal renal function (79.4% vs. 89.2%, respectively; p = 0.018). Compared with those with preserved eGFR, patients with CKD had significantly higher all-cause and cardiovascular mortality (p = 0.001 and p < 0.001, respectively) as well as increased incidence of possible stent thrombosis (Fig. 1, Table 4). A total of 23 all stent thrombosis was recorded in the cohort, which occurred between 4 and 375 days after PCI. Of these, 5 occurred within the first 30 days. No difference in the time of occurrence of stent thrombosis was observed between the 2 groups.
Impact of P2Y12 inhibition by clopidogrel on cardiovascular outcomes
In the whole population, the presence of a LR status was associated with higher rates of all-cause mortality as well as of possible and all stent thrombosis (Table 5).
Interaction between baseline renal function and degree of P2Y12 inhibition by clopidogrel on cardiovascular outcomes
In the no-CKD group, no statistically significant differences in any of the primary and secondary end points were observed between patients with normal and those with low response to clopidogrel (Table 6). In contrast, among patients with CKD, the incidence of all-cause mortality, cardiovascular mortality, possible stent thrombosis, all stent thrombosis, and MACE was significantly higher in the low responders compared with the responder subgroup (Table 6, Figs. 2 and 3). To gain insight into the relationship between PRI levels and MACE among CKD patients, data were also analyzed according to quartiles of PRI (Table 7). At the end of follow-up, the proportion of patients on dual antiplatelet therapy in the CKD group was similar between low responder and responder patients (85.5% and 87%, respectively; p = 0.371).
Predictors of cardiac death and MACE
By univariate Cox analysis, Killip class III to IV, the use of drug-eluting stents (DES), a diagnosis of CKD, and a low response to clopidogrel (PRI <61%) were significant predictors of cardiac death (Table 8). The occurrence of MACE was directly related to Killip class III to IV, the use of DES, and the presence of 3-vessel disease, whereas planned PCI was associated with a lower risk of MACE. Multivariate Cox regression analysis identified Killip III to IV, the use of DES, and the interaction between CKD and low response to clopidogrel as independent predictors of cardiac death (Table 9). In contrast, the interactions between a diagnosis of type 2 diabetes and low responder or type 2 diabetes and CKD were not independent predictors of cardiac death.
The main finding of this study is that the presence of low platelet response to clopidogrel is associated with increased all-cause mortality, cardiac death, possible and all stent thrombosis, and MACE after PCI in patients with CKD. However, in patients with preserved eGFR, these outcomes do not appear to differ between those with normal and those with reduced platelet response to clopidogrel. In addition, our data confirm the association between the presence of CKD and worse all-cause mortality and cardiovascular outcomes.
Several studies in the setting of STEMI (19), NSTEMI, and elective PCI (20,21) have reported a negative association between CKD and stent thrombosis, post-procedure ischemic events, and mortality in patients undergoing PCI (12,19–24). In a large retrospective analysis, the presence of decreased renal function had a similar negative impact on mortality and morbidity as diabetes mellitus (12). In our investigation, the increase in all-cause and in cardiovascular death rates observed in the participants with CKD is in line with a previous report of a 5-fold higher mortality at 1 year post-PCI in patients with moderate renal insufficiency (12). However, it should be emphasized that this latter study had enrolled lower-risk patients. By comparison, our study population mainly consisted of CKD patients with acute coronary syndrome patients (30.1% with STEMI and 39.6% with NSTEMI). In the setting of acute myocardial infarction, 1-year mortality rate observed in moderate CKD patients was reported to be 12.7% as compared with 2.4% in non-CKD patients (19). The mechanisms by which CKD impacts the clinical outcome are likely multifactorial, and may include dyslipidemia, homocysteinemia, insulin resistance, increased oxidative stress, extensive coronary calcification, endothelial damage (25), reduced number and function of endothelial progenitor cells (26), abnormal platelet–endothelial cell interactions, and a prothrombotic state (27–31). A reduced bioavaibility of nitric oxide (NO) secondary to increased oxidative stress has been proposed to play a major role in CKD-associated endothelial dysfunction, possibly leading to enhanced vasoconstriction and platelet adhesion/activation (32).
Impact of CKD on platelet P2Y12 inhibition by clopidogrel
Whether CKD affects clopidogrel pharmacokinetics has not been conclusively clarified. Although it has been suggested that the extent of platelet inhibition by clopidogrel is comparable between patients on long-term hemodialysis and those with normal renal function (33), other evidence indicates that the lack of platelet responsiveness to clopidogrel might be more pronounced in patients with CKD (34,35). In our study, the degree of P2Y12 inhibition by clopidogrel using the VASP assay was not significantly different in the CKD and non-CKD groups. Likewise, the proportion of LR patients was equivalent in both groups. Taken together, these observations do not support the concept of a specific impairment of the P2Y12 pathway due to CKD. However, given the limited number of patients with severe CKD enrolled in the present registry, we could not definitely exclude that an altered platelet response to clopidogrel occurs in these clinical settings.
Impact of low platelet response to clopidogrel in CKD patients
In our registry, the interaction between CKD and low response to clopidogrel was associated with an increased risk of cardiac death at 9 months. Of note, the prognosis of CKD with a normal response to clopidogrel appears comparable to that observed in patients with preserved eGFR. Interestingly, the Kaplan-Meier curve profile suggests a late catch-up with similar MACE rates after 400 days (Fig. 3). This observation might indicate that the impact on MACE of the responsiveness to clopidogrel is less important in CKD patient in the late follow-up after PCI. However, since cardiovascular mortality (Fig. 2) still increases between groups even after 300 days, late follow-up of our data should be interpreted with caution. Additional study on a larger cohort and longer follow-up should be performed. This observation might suggest that the achievement of optimal P2Y12 platelet inhibition, especially in the first year, is an important therapeutic goal in CKD patients. Although several studies have emphasized the deleterious impact of low platelet inhibition by thienopyridines on worsened cardiovascular outcome in unselected patients, the question of whether impaired platelet inhibition by thienopyridines specifically impairs cardiovascular prognosis was not investigated in CKD patients. In this setting, the benefit of thienopyridines is still controversial (36). Indeed, after PCI, post hoc analyses of the CREDO (Clopidogrel for the Reduction of Events During Observation) trial have suggested that in patients with mild or moderate CKD (corresponding to stages II and III), clopidogrel may not have the same beneficial effect as in patients with normal renal function. In patients with normal renal function treated for 1 year with clopidogrel, the rate of MACE (death, myocardial infarction, and stroke) was significantly reduced compared with placebo. However, in patients with mild or moderate CKD, clopidogrel therapy was not associated with significant benefit (37). This negative result in CKD patients might be related to the relatively low dose of clopidogrel in this trial (loading dose 300 mg, maintenance dose 75 mg). The interindividual variability of the platelet response to a loading dose (300 mg) or to the long-term dose of 75 mg/day has been clearly demonstrated. In our experience, such a regimen is associated with a prevalence of patients with low platelet P2Y12 inhibition of approximately 30% to 40% (38,39). It is reasonable to speculate that a more potent P2Y12 inhibition may favorably affect the poor prognosis of CKD patients. Indeed, in TRITON–TIMI 38 (Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition With Prasugrel–Thrombolysis In Myocardial Infarction 38), the reduction in the risk of stent thrombosis (definite/probable) associated with prasugrel use was independent of the presence of CKD (40,41).
Taken together, our data suggest that the evaluation of the platelet responsiveness to clopidogrel using the VASP assay might be of great value for the management of CKD patients treated by PCI. In addition, in CKD patients treated by PCI, optimal inhibition of the P2Y12 pathway could be an important target to reduce ischemic events. This hypothesis needs further evaluation, especially in light of the described increased bleeding associated with more drastic P2Y12 inhibition or renal insufficiency.
Single time-point laboratory assessment represents a common limitation to most studies assessing the prognostic implication of platelet function or other biological variables such as serum creatinine. The impact of contrast toxicity that may account to worsen clinical outcome after PCI was not investigated. The timing of the VASP analysis was not uniform. VASP testing was not compared in this study with other techniques of platelet function. We could not exclude that a disproportionate noncompliance to clopidogrel in CKD low responder patients could have affected the cardiovascular outcome. The potential impact of increasing the doses of clopidogrel has not been investigated in patients detected as low responders. Stent implantation (bare-metal stents vs. DES) was not randomized. The cardiovascular events were not adjudicated by an independent committee. Given the relatively low number of cardiovascular death recorded in this registry, multivariate analysis should be interpreted with caution and the findings viewed as exploratory and/or hypothesis generating. As with similar evaluation of registry data, there are inherent limitations in this type of study, mainly related to known or unknown confounding factors.
Taken together, our data suggest that the presence of low platelet response to clopidogrel is associated with worse outcome after PCI in patients with CKD. The evaluation of the responsiveness to clopidogrel using the VASP assay could be useful for the management of CKD patients treated by PCI. A possible beneficial impact of more potent P2Y12 inhibition by a higher dose of clopidogrel, prasugrel, or ticagrelor (42) needs further evaluation.
The authors have reported that they have no relationships to disclose.
- Abbreviations and Acronyms
- chronic kidney disease
- drug-eluting stent(s)
- estimated glomerular filtration rate
- major adverse cardiac events
- non–ST-segment elevation myocardial infarction
- percutaneous coronary intervention
- ST-segment elevation myocardial infarction
- vasodilator-stimulated phosphoprotein
- Received May 11, 2010.
- Revision received September 8, 2010.
- Accepted September 28, 2010.
- American College of Cardiology Foundation
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