Bleeding-associated outcomes with preoperative clopidogrel use in on- and off-pump coronary artery bypass

Clopidogrel use prior to coronary artery bypass graft surgery in patients presenting with acute coronary syndromes is associated with a greater incidence of procedural related morbidity. We studied the impact of clopidogrel pre-treatment in patients undergoing off-pump versus on-pump coronary revascularization. This report describes a post hoc analysis of 431 on-pump and 165 off-pump cases from a retrospective multicenter study of the impact of preoperative (within 5 days) clopidogrel use on bleeding related outcomes and surgical reintervention. Logistic regression was used to analyze the outcomes with respect to surgery type and clopidogrel exposure while using a propensity score risk adjustment for off-pump surgery. The hospital length of stay (9.3 ± 5.4 days vs. 8.9 ± 5.3 days, p = 0.35), major bleeding (21% vs. 20%, p = 0.74) and reoperation (3.7% vs. 4.8%, p = 0.53) were similar between on-pump and off-pump, respectively. In both surgical cohorts, recent clopidogrel use was associated with a greater incidence of major bleeding, reoperation, and transfusion. After multivariable adjustment, the odds ratio of major bleeding (1.76, 95% confidence interval 0.88-3.52 on-pump; 2.37, 95% confidence interval 1.06-5.30 off-pump) and reoperation (4.52, 95% confidence interval 0.58-36.6 in on-pump; 7.05, 95% confidence interval 0.82-60.5 in off-pump) was increased in clopidogrel-treated patients compared to no clopidogrel. Major bleeding and reoperation did not differ significantly between patients undergoing on- or off-pump surgery. Clopidogrel treatment within 5 days prior to surgery increased the risk of bleeding and reoperation in all CABG patients irrespective of whether surgery was performed on- or off-pump.     

A brief review of the past and future of platelet P2Y12 antagonist

ADP plays a pivotal role in localized platelet activation and recruitment, and, with that, in the maintenance of thrombus integrity, making it a suitable target for the control of intravascular thrombosis. The limited distribution of one of its receptors, the P2Y12 receptor, primarily to platelets makes it an especially attractive pharmacologic target. For the last several decades the thienopyridine family of P2Y12 antagonists have provided the vast majority of clinical data confirming the clinical benefit of selective P2Y12 inhibition. Recently, new thienopyridine plus nonthienopyridine P2Y12 antagonists have become available or are being studied that will further improve our treatment of patients with coronary disease.     

Variable response to antiplatelet therapy: what does it mean to clinicians?

Ex vivo tests of platelet function show that platelet function and the response to antiplatelet therapy vary markedly from person to person. But just how clinically significant are ex vivo measurements of platelet function, and will changes we make based on such information translate into improved outcomes for patients? The authors summarize what is known and not known about the impact and clinical significance of variable response to antiplatelet therapy.     

Clopidogrel: How good is it and how does it work?

Until recently, long-term antiplatelet therapy for the treatment and prevention of the complications of atherothrombotic disease was limited to aspirin. Although an incredibly costeffective therapy, in placebo-controlled clinical trials approximately 75% of patients at risk continue to experience thrombotic events despite chronic aspirin therapy. The availability of the thienopyridines, in particular clopidogrel, represents an important addition to the physician’s armamentarium. A number of clinical trials have confirmed the efficacy of the combination of clopidogrel and aspirin therapy compared with aspirin alone, with multiple other important largescale clinical trials currently ongoing. The exact mechanism of this benefit is still being elucidated but is clearly related to the inhibition of the many consequences of platelet activation—vascular inflammation, endothelial dysfunction, and localized angiogenesis/mitogenesis—and not just aggregation.     

Patients with prior myocardial infarction, stroke, or symptomatic peripheral arterial disease in the CHARISMA trial.

OBJECTIVES: The purpose of this study was to determine the possible benefit of dual antiplatelet therapy in patients with prior myocardial infarction (MI), ischemic stroke, or symptomatic peripheral arterial disease (PAD). BACKGROUND: Dual antiplatelet therapy with clopidogrel plus aspirin has been validated in the settings of acute coronary syndromes and coronary stenting. The value of this combination was recently evaluated in the CHARISMA (Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management, and Avoidance) trial, where no statistically significant benefit was found in the overall broad population of stable patients studied. METHODS: We identified the subgroup in the CHARISMA trial who were enrolled with documented prior MI, ischemic stroke, or symptomatic PAD. RESULTS: A total of 9,478 patients met the inclusion criteria for this analysis. The median duration of follow-up was 27.6 months. The rate of cardiovascular death, MI, or stroke was significantly lower in the clopidogrel plus aspirin arm than in the placebo plus aspirin arm: 7.3% versus 8.8% (hazard ratio [HR] 0.83, 95% confidence interval [CI] 0.72 to 0.96, p = 0.01). Additionally, hospitalizations for ischemia were significantly decreased, 11.4% versus 13.2% (HR 0.86, 95% CI 0.76 to 0.96, p = 0.008). There was no significant difference in the rate of severe bleeding: 1.7% versus 1.5% (HR 1.12, 95% CI 0.81 to 1.53, p = 0.50); moderate bleeding was significantly increased: 2.0% versus 1.3% (HR 1.60, 95% CI 1.16 to 2.20, p = 0.004). CONCLUSIONS: In this analysis of the CHARISMA trial, the large number of patients with documented prior MI, ischemic stroke, or symptomatic PAD appeared to derive significant benefit from dual antiplatelet therapy with clopidogrel plus aspirin. Such patients may benefit from intensification of antithrombotic therapy beyond aspirin alone, a concept that future trials will need to validate. (Clopidogrel for High Atherothrombotic Risk and Ischemic Stabilization, Management, and Avoidance [CHARISMA]; http://clinicaltrials.gov/ct/show/NCT00050817?order=1; NCT00050817).     

Platelet function monitoring in patients with coronary artery disease.

Studies focused on patient responsiveness to antiplatelet therapies, particularly aspirin and clopidogrel, have increased in recent years. However, the relations of in vivo platelet function and adverse clinical events to results of ex vivo platelet function tests remain largely unknown. This article describes current methods of measuring platelet function in various clinical and research situations and their advantages and disadvantages, reviews evidence for antiplatelet response variability and resistance, discusses the potential pitfalls of monitoring platelet function, and demonstrates emerging data supporting the positive clinical and treatment implications of platelet function testing.     

An analysis of mortality rates with dual-antiplatelet therapy in the primary prevention population of the CHARISMA trial.

AIMS: To examine the unanticipated, excess mortality observed in patients randomized to clopidogrel and aspirin vs. aspirin alone in the prespecified 'asymptomatic' subgroup of CHARISMA, we investigated whether dual-antiplatelet therapy may be associated with adverse cardiovascular (CV) events in a primary prevention population. METHODS AND RESULTS: Of 15 603 patients enrolled, 3284 were initially categorized as asymptomatic with CV risk factors, but 995 had a prior CV event, leaving 2289 patients to represent the primary prevention cohort. This subset was compared with 13 148 symptomatic patients with established vascular disease and both were evaluated for CV death and bleeding. A multivariate analysis analysed predictors of CV death in this group. No post mortem data were available. Compared with aspirin alone, a significant increase in CV death (P = 0.01) was observed in patients receiving dual-antiplatelet therapy in the asymptomatic population. Within the primary prevention cohort, this excess CV death was not significant (P = 0.07). Multivariate analysis of the primary prevention group showed a trend towards excess CV death (P = 0.054; HR 1.72; CI 0.99-2.97) with dual-antiplatelet therapy (aspirin plus clopidogrel). Other independent predictors of CV death included increasing age, hypertension, atrial fibrillation, and a history of heart failure. There was a non-significant increase in moderate or severe bleeding (P = 0.218) with dual-antiplatelet therapy; thus, bleeding was an unlikely explanation for the excess event rate. CONCLUSION: These findings do not support the use of dual-antiplatelet therapy with clopidogrel and aspirin in a primary prevention population. In this subgroup analysis, CV death occurred more frequently than anticipated. The cause of this apparent harm is not elucidated, may represent play of chance, but requires further prospective evaluation.     

Variability in platelet responsiveness to clopidogrel among 544 individuals

OBJECTIVES: We sought to describe the responses of patients to clopidogrel using ex vivo measures of platelet aggregation and activation in a large, heterogeneous population. BACKGROUND: Recently, a number of reports, using various definitions, have dichotomized patients who are treated with clopidogrel into a minority of "non-responders" and a majority of "responders." Such classifications imply that treatment leads to an all-or-none response, with potentially important clinical implications. METHODS: We conducted secondary post-hoc analyses of a dataset consisting of volunteers (n = 94) and patients after coronary stenting (n = 405), with heart failure (n = 25), and after stroke (n = 20). RESULTS: The response of subjects to clopidogrel followed a normal, bell-shaped distribution, with a mean and standard deviation of 41.9 +/- 20.8% when aggregation was induced by 5 mumol/l of adenosine diphosphate. When hyporesponsiveness and hyper-responsiveness to clopidogrel were considered to be two standard deviations less than and greater than the mean, respectively, the prevalence of hyporesponsiveness and hyper-responsiveness in these patients was 4.2% and 4.8%, respectively. Pretreatment platelet activity and clinical characteristics were not associated with responsiveness to clopidogrel. CONCLUSIONS: Individuals receiving clopidogrel exhibit a wide variability in response that follows a normal distribution. The clinical implications of this variability are unknown but potentially are important. Clinical trials are needed to define whether hyporesponders to clopidogrel are at increased risk for thrombotic events and whether hyper-responders are at increased risk for bleeding. If so, the individualization of antiplatelet therapy, including clopidogrel dosing, may be possible in the future but will require the ability to easily and reproducibly measure responsiveness by a method that has been proven to be predictive of clinical events.