Balancing the benefit and risk of oral antiplatelet agents in coronary artery bypass surgery

Platelet Function Test in Coronary Artery Bypass Grafting: Does It Predict Postoperative Bleeding?

Background Patients undergoing on-pump coronary artery bypass grafting (CABG) are at increased risk of perioperative bleeding and morbidity associated with transfusion as a result of acquired and pharmacologically induced impaired platelet function.

Settings and Design In this a prospective observational study where 52 patients underwent on-pump CABG were analyzed with ROTEM platelet aggregometry.

Materials and Methods Patients were assigned to the “nonexcessive” and “excessive” postoperative bleeding groups according to the postoperative chest tube drainage over 24 hours. Platelet function was assessed by ROTEM platelet using three different activators (arachidonic acid, adenosine diphosphate, and thrombin receptor-activating peptide), at two perioperative time points (T1, before heparinization and T2, 5–10 minutes after protamine administration).

Results There were no differences regarding demographic, pre–cardiopulmonary bypass (CPB) platelet count and antiplatelet therapy. Platelet function was impaired over the time course in all parameters with three different activators. At T2 point, area under the curve (AUC) of all the three platelet indices, that is, TRAPTEM, ARATEM, and ADPTEM, showed significant difference between excessive and nonexcessive groups. At both T1 and T2 points, the amplitude after 6 minutes (A6) and maximum slope (MS) parameters of TRAPTEM, ARATEM, and ADPTEM tests were not significantly different in excessive and nonexcessive groups. At T1 point, AUC was also not significantly different in all three ROTEM platelet tests. Results after protamine administration showed correlation with postoperative chest tube drainage. Cut-off values, as determined by receiver operating characteristics (ROC) analyses, had a consistently weak positive predictive value for all tests at T2 time point, whereas negative predictive values were higher.

Conclusion Platelet function analysis using ROTEM platelet can help to exclude platelet dysfunction as the reason for bleeding after cardiac surgery. Point-of-care platelet function analysis, particularly in combination with viscoelastic testing can reduce perioperative bleeding and transfusion requirements, as well as improve patient outcomes in cardiac surgery.

Role of Platelet Function Test in Predicting Postoperative Bleeding Risk after Coronary Artery Bypass Grafting: A Prospective Observational Study

Patients undergoing cardiac surgery are at risk of excessive bleeding and its associated complications. Excessive bleeding during and after cardiac surgery has an incidence of ~20%. Massive bleeding and subsequent requirement for blood product administration and mediastinal reexploration are associated with significant morbidity and mortality. Postoperative, nonsurgical bleeding in cardiac surgical patients is often multifactorial. Platelet dysfunction, excessive fibrinolysis, hypothermia, preoperative anemia, and deficiency of coagulation factors or their dilution are all suggested etiologies of postoperative bleeding. In the Arachidonic Acid Thromboelastometry (ARATEM) test, platelets are activated with arachidonic acid; in Adenosine diphosphate Thromboelastometry (ADPTEM) test, platelets are activated with adenosine diphosphate; and in TRAPTEM test, platelets are activated with thrombin receptor-activating peptide 6. Measurement time is 6 minutes, and results are expressed in three different parameters: A6 (amplitude at 6 minutes, in Ohm); MS (maximum slope of the aggregation curve in Ohm/min), and AUC (area under the curve in Ohm.min). Algorithm-based point-of-care platelet function testing helped us to preemptively give the right blood component therapy, avoiding fibrinolytic bleeding in the postoperative period.

Relationship between maximum clot firmness in ROTEM® and postoperative bleeding after coronary artery bypass graft surgery in patients using clopidogrel

Background:

The aim of the present study was to investigate the relationship between maximum clot firmness (MCF) in rotational thromboelastometry (ROTEM^®) and postoperative bleeding in patients on clopidogrel after emergency coronary artery bypass graft surgery (CABG).

Methods:

This observational study recruited 60 patients posted for emergency CABG following unsuccessful primary percutaneous coronary intervention (PCI) while on 600 mg of clopidogrel. The study population was divided into 2 groups on the basis of their MCF in the extrinsically activated thromboelastometric (EXTEM) component of the (preoperative) ROTEM^® test: patients with MCF <50 mm (n = 16) and those with MCF ≥50 mm (n = 44). Postoperative chest tube drainage amount, need for blood product transfusion, postoperative complications, and duration of mechanical ventilation after CABG were recorded.

Results:

No significant differences were observed between the two groups regarding duration of surgery, cardiopulmonary bypass, and aortic cross-clamp time. Chest tube drainage at 6, 12, and 24 h after Intensive Care Unit admission were significantly higher in the patients with MCF below 50 mm. The need for blood product transfusion was higher in the group with MCF <50 mm. In patients who experienced postoperative bleeding of 1000 mL or more, the ROTEM^® parameters of INTEM (Intrinsically activated thromboelastomery) α and MCF, EXTEM α and MCF, and HEPTEM (INTEM assay performed in the presence of heparinase) MCF (but not FIBTEM (Thromboelastometric assay for the fibrin part of the clot) values) were significantly lower than those with postoperative bleeding <1000 mL (P ≤ 0.05).

Conclusions:

When platelet aggregometry is not available, the ROTEM^® test could be useful for the prediction of increased risk bleeding after emergency CABG in patients who have received a loading dose of clopidogrel.

Predicting Bleeding Risk by Platelet Function Testing in Patients Undergoing Heart Surgery

BACKGROUND

Predicting bleeding events in patients with coronary artery bypass grafting (CABG) represents an unmet medical need that may improve CABG outcomes.

HYPOTESIS

To assess the potential link between platelet function testing and bleeding risk in patients undergoing CABG.

METHODS

Platelet aggregation and clinical outcomes in 478 patients treated with aspirin and/or clopidogrel were retrospectively analyzed. Platelet activity was assessed prior to CABG with arachidonic acid (ASPI Test), and adenosine diphosphate(ADP Test) utilizing multiple-electrode aggregometry.

RESULTS

In the study group of 478 patients, mean age was 65.2±15.2 years; 138 were women. The majority of patients (n = 198) underwent on-pump surgery, with 162 undergoing off-pump and 30 undergoing minimally invasive surgery. Forty-eight patients received artificial valve implantation alone, and 40 received valve implantation in combination with CABG. The analysis of the entire pool revealed that an ASPI test value <407 area under curve per minute (AUC*min) may be useful in predicting postoperative drainage. In CABG patients only, an ASPI test value <271 AUC*min predicted the need for red blood cell concentrate transfusion following surgery. In patients who stopped clopidogrel for up to 5 days before surgery, the ADP test failed to exhibit prognostic utility for predicting bleeding risk.

CONCLUSIONS

In patients undergoing heart surgery, an ASPI test value <407 AUC*min may predict higher postoperative drainage, whereas <271 AUC*min may be linked to postoperative use of red blood cell concentrate.

Risk Factors for Post-Coronary Artery Bypass Grafting (CABG) Atrial Fibrillation and the Role of Aspirin and Beta Blockers in its Prevention

Background: Atrial fibrillation/flutter (AF) is the most common arrhythmia following coronary artery bypass grafting (CABG) and it increases morbidity and mortality associated with this procedure. The purpose of this study was to evaluate the predictability of this arrhythmia using previously identified risk factors and to assess the efficacy of recommended prophylactic beta blocker (BB) therapy in the prevention of post CABG AF. Methods: We performed a retrospective chart analysis of consecutive patients undergoing elective CABG during 1 year period. Patients who developed new onset AF after the surgery were designated as cases and those who did not, as controls. 41 different variables were analyzed using Chi-square test and independent sample t-test. Multivariate analysis was carried out using logistic regression model. Results: 23% patients undergoing CABG developed AF during post-operative period. Statistically significant differences were observed between the two groups in terms of age, use of peri-operative Aspirin (ASA), current smoking, previous history of AF, left atrial size, history of congestive heart failure (CHF) and brain natriuretic peptide (BNP) levels. In terms of prophylactic therapy, preoperative BB did not independently protect against post CABG AF. On multivariate analysis, only age, use of ASA and previous history of AF remained as independent predictors of post CABG AF. Conclusion: In our study population, the use of preoperative BB did not independently decrease the risk of post-CABGAF. Age, peri-operative ASA use and previous history of AF remained strong independent predictors of post- operative AF.

Managing adverse effects and drug-drug interactions of antiplatelet agents

Antiplatelet therapies have reduced the frequency of adverse events associated with plaque rupture in several clinical situations. These therapies include established antiplatelet agents (such as aspirin, clopidogrel, or glycoprotein IIb/IIIa inhibitors) as well as new agents (such as prasugrel and ticagrelor). In this Review, we address the most important adverse events of antiplatelet therapy, including hemorrhage, hematologic reactions, and dyspnea. We discuss strategies to reduce the incidence of complications and outline potential methods to manage adverse reactions. Interactions between antiplatelet agents and other drugs--such as proton-pump inhibitors, calcium-channel blockers, statins, warfarin, or NSAIDs--are also addressed, as well as specific issues relating to the use of antiplatelet therapies in elderly patients.

Early antiplatelet therapy in coronary artery bypass grafting: a calculated benefit

Studies have demonstrated that antagonists of platelet activity, including aspirin and clopidogrel, reduce the risk of major adverse events in patients with acute coronary syndromes. Although antiplatelet agents also convey an increased risk of bleeding, particularly in patients proceeding to coronary artery bypass graft surgery, in most cases, the benefits of early initiation of antiplatelet therapy outweigh the risks. The purpose of this review is to distinguish perceived and actual risk versus the benefit associated with early antiplatelet therapy to help clinicians make informed decisions on using these agents in an acute setting where patients may require coronary artery bypass grafting.

Postoperative development of aspirin resistance following coronary artery bypass

BACKGROUND

Aspirin therapy is known to substantially reduce mortality and the rate of ischaemic complications after coronary artery bypass grafting (CABG). Rates of perioperative aspirin resistance cited in the literature are up to 50% and could be influenced by extracorporeal circulation. Thus, aspirin resistance after CABG may have a significant clinical relevance.

MATERIALS AND METHODS

In 59 patients undergoing CABG (on-pump, off-pump and combined procedures) aspirin resistance was investigated by arachidonic acid induced platelet aggregometry. Clinical relevance was assessed with 12-month follow up.

RESULTS

Two types of resistance were observed: A preoperative resistance (despite oral aspirin or in vitro addition) was present in 29% and a postoperative developing type was seen in 49% resulting in only 22% of patients with a 'normal' reaction to aspirin. If patients were already on oral aspirin at admission, the rate of resistance was significantly reduced. Off-pump surgery or pump-times exceeding 120 min had no significant impact on resistance. During the 12-month follow up (98.3%), there were three deaths (one stroke, one intestinal ischaemia, one mediastinitis after postoperative delirium) in patients with the perioperative resistance and none in other patients (P = 0.345). In none of those patients who presented with perioperative aspirin resistance, could this aspirin resistance be demonstrated when tested again after 12 months?

CONCLUSIONS

Aspirin resistance is a transient phenomenon present in the majority of patients undergoing CABG. The three deaths in the resistant group may - although not statistically significant - indicate the possibility of a worse outcome for patients with aspirin resistance.

Effects of a waiting period after clopidogrel treatment before performing coronary artery bypass grafting

STUDY OBJECTIVE

To assess the effects of a waiting period after clopidogrel treatment before coronary artery bypass grafting (CABG). Design. Single-center, prospective, observational study.

SETTING

Cardiothoracic surgery intensive care unit at a university-affiliated medical center.

PATIENTS

One hundred consecutive patients who received clopidogrel and were scheduled to undergo primary CABG. In 64 of these patients, CABG was delayed at least 5 days after clopidogrel treatment (group A). The other 36 patients received clopidogrel treatment within 5 days of undergoing CABG (group B).

MEASUREMENTS AND MAIN RESULTS

Data were collected on patient demographics, time of last clopidogrel dose, preoperative anticoagulant and/or antiplatelet agents administered, surgical characteristics, intraoperative transfusions, blood products transfused, and chest tube output for 24 hours after surgery. No significant differences in baseline characteristics or intraoperative variables (number of bypasses, aortic cross-clamp time, and cardiopulmonary bypass time) were noted between the two groups. Mean +/- SD number of packed red blood cell units/patient was 1.1 +/- 1.4 in group A versus 2.1 +/- 2.5 in group B (p=0.009). Mean +/- SD number of platelet units/patient transfused was 0.5 +/- 0.9 in group A versus 1.9 +/- 1.6 in group B (p<0.001). When comparing a subset of 21 patients who received clopidogrel within 72 hours of surgery with the 64 whose CABG was delayed at least 5 days after clopidogrel treatment, the transfusion rates were significantly higher (95% vs 52%, p<0.05). Specifically, the mean +/- SD number of transfused units/patient of red blood cells (3.1 +/- 2.8 vs 1.1 +/- 1.4, p<0.005) and platelets (2.6 +/- 1.5 vs 0.5 +/- 0.9, p<0.007) was greater in patients who received clopidogrel within 72 hours of surgery.

CONCLUSION

A strategy to delay CABG after clopidogrel treatment led to reduced blood product administration. The optimal waiting period after clopidogrel treatment is not known but appears to be at least 5 days before CABG.

Contemporary issues in clopidogrel therapy: new evidence shaping clinical practice

Antiplatelet therapy is a cornerstone in the management of acute coronary syndromes. Clopidogrel produces irreversible inhibition of the platelet adenosine diphosphate receptor, thereby attenuating activation and aggregation of platelets. Clopidogrel has been shown to prevent stent thrombosis in patients undergoing percutaneous coronary intervention (PCI) and reduces major adverse cardiovascular events in patients with unstable angina or non-ST-segment elevation myocardial infarction (non-STEMI). Recent studies have left clinicians with many questions regarding the role and dosing regimens of clopidogrel in STEMI, PCI, and primary or secondary prevention. Based on an analysis of the data, clopidogrel should be given in addition to aspirin and fibrinolytic therapy to patients with STEMI. In patients undergoing PCI, a loading dose of clopidogrel 600 mg should be given if the procedure needs to be performed within 15 hours of initial presentation. If PCI can be delayed for 15 hours or more, a loading dose of 300 mg can be used. Evidence also suggests that clopidogrel should not be prescribed for primary prevention in high-risk patients.

Use of antiplatelet drugs in secondary prevention in older persons with atherothrombotic disease

Unless there are contraindications to the use of aspirin, aspirin should be used in treating patients with acute myocardial infarction (MI) and continued indefinitely to reduce vascular death, nonfatal MI, and nonfatal stroke. Clopidogrel added to aspirin has been shown to be beneficial in the treatment of patients with acute ST-elevation MI. Patients with unstable angina or non-ST-elevation MI should be treated with aspirin plus clopidogrel for at least 9 months to reduce vascular death, nonfatal MI, and nonfatal stroke. Patients with prior MI should be treated indefinitely with aspirin and with clopidogrel if aspirin is contraindicated. Patients with ischemic stroke should be treated with either aspirin or clopidogrel indefinitely. Extended release dipyridamole plus low dose aspirin has been shown to be more efficacious than low dose aspirin in only one large study, and is associated with an insignificant increase in nonfatal MI and vascular death over low dose aspirin alone. Clopidogrel is significantly more effective than aspirin in reducing vascular death, nonfatal MI, and nonfatal stroke in patients with peripheral arterial disease.

Effects of preoperative aspirin and clopidogrel therapy on perioperative blood loss and blood transfusion requirements in patients undergoing off-pump coronary artery bypass graft surgery

OBJECTIVE

Preoperative exposure to clopidogrel and aspirin significantly increases postoperative bleeding in patients undergoing on-pump coronary artery bypass graft surgery. Off-pump coronary bypass grafting has been proposed as an alternative technique to attenuate postoperative bleeding associated with clopidogrel. This study aimed to determine the effects of aspirin and clopidogrel therapy on perioperative blood loss and blood transfusion requirements in off-pump coronary artery bypass grafting.

METHODS

One hundred six patients scheduled for off-pump coronary artery bypass grafting were divided into three groups: aspirin and clopidogrel discontinued more than 6 days before surgery (group 1, n = 35), aspirin and clopidogrel continued until 3 to 5 days before surgery (group 2, n = 51), and both medications continued within 2 days of surgery (group 3, n = 20). Thromboelastographic tracings were analyzed before induction of anesthesia. Routine coagulation profiles were measured before and after surgery. A cell salvage device was used during surgery and salvaged blood was reinfused. Chest tube drainage and blood transfusion requirement were recorded postoperatively.

RESULTS

Patient characteristics, operative data, and thromboelastographic tracings were similar among the groups. There were significant decreases in hematocrit level and platelet count and prolongation in prothrombin time postoperatively in all groups without any intergroup differences. The amounts of perioperative blood loss and blood transfusion required were all similar among the groups.

CONCLUSION

Preoperative clopidogrel and aspirin exposure even within 2 days of surgery does not increase perioperative blood loss and blood transfusion requirements in patients undergoing elective off-pump coronary artery bypass grafting.

Clinical update on the therapeutic use of clopidogrel: treatment of acute ST-segment elevation myocardial infarction (STEMI)

The pathogenesis of ST-elevation myocardial infarction (STEMI) involves plaque disruption, platelet aggregation and intracoronary artery thrombus formation. Aspirin is the cornerstone of antiplatelet therapy in patients with STEMI, reducing the risk of recurrent myocardial infarction or death during the acute phase and long term by about one-quarter. Recent large randomized trials have demonstrated that the addition of clopidogrel to aspirin reduces the risk of major ischemic events by up to a further one-third in patients with STEMI treated with fibrinolytic therapy and undergoing percutaneous coronary intervention, with no significant increase in bleeding. Thus, dual antiplatelet therapy with the combination of clopidogrel and aspirin is becoming the new standard of care for the management of patients with STEMI.

Benefits and risks of clopidogrel pretreatment before coronary artery bypass grafting in patients with ST-elevation myocardial infarction treated with fibrinolytics in CLARITY-TIMI 28

The Clopidogrel as Adjunctive Reperfusion Therapy-Thrombolysis in Myocardial Infarction 28 (CLARITY-TIMI 28) trial was a randomized, double-blind, placebo-controlled study of clopidogrel in 3,491 patients receiving fibrinolytic therapy for ST-segment elevation myocardial infarction. Patients were randomized to clopidogrel or placebo begun at the time of fibrinolysis. This analysis reports the outcomes among the 136 patients in the trial population who underwent coronary artery bypass grafting (CABG) during the index hospitalization. There was no difference in the rates of TIMI major or minor bleeding between the clopidogrel and placebo groups from randomization to the end of follow-up (13.6% vs. 14.3%, P = 1.0) or from the time of CABG to the end of follow-up (9.1% vs. 11.4%, P = 0.78). When any day for study medication discontinuation < or = 5 days prior to CABG was chosen as a cut point to evaluate bleeding risk for clopidogrel vs. placebo, there was no excess bleeding in the clopidogrel group. Among patients undergoing CABG, there was a trend toward reduction in the risk of cardiovascular death, recurrent MI, or recurrent ischemia requiring urgent revascularization at 30 days for those taking clopidogrel (OR 0.66, 95% CI 0.27-1.5; P = 0.37), consistent with the benefit seen in the overall trial population (OR 0.80, CI 0.65-0.97; P = 0.03). In conclusion, early clopidogrel treatment among CLARITY-TIMI 28 patients undergoing CABG was not associated with an increase in the rate of peri-operative bleeding and showed a trend toward reduction in 30-day ischemic events.

Effect of timing of clopidogrel administration on 30-day clinical outcomes: 300-mg loading dose immediately after coronary stenting versus pretreatment 6 to 24 hours before stenting in a large unselected patient cohort

BACKGROUND

The aim of our prospective multicenter Clopidogrel Registry was to evaluate the efficacy and safety of a 300-mg loading dose of clopidogrel at the time of ad hoc stenting in patients with suspected coronary artery disease who were not pretreated with clopidogrel for any reason, and to compare the 30-day clinical event rates with the outcome of patients pretreated with a loading dose of clopidogrel 6 to 24 hours before stenting.

METHODS

Between March 2002 and February 2004, 4160 consecutively included patients received a 300-mg loading dose of clopidogrel immediately after (group 1, n = 2679) or 6 to 24 hours before stenting (group 2, n = 1481).

RESULTS

The primary end point (triple composite end point of acute myocardial infarction, all-cause death, and urgent repeat target vessel revascularization) at 30 days occurred in 4.74% versus 2.77% in groups 1 and 2, respectively (P = .002). The secondary end point events, the stent thrombosis, occurred significantly more frequently in group 1, with a trend toward increase in incidence of death, target vessel revascularization, or need for glycoprotein IIb/IIIa antagonists during percutaneous coronary intervention. Pretreatment with clopidogrel was associated with more major bleeding (secondary safety end point) (0.41% vs 1.35% in groups 1 and 2, respectively; P = .001).

CONCLUSIONS

The results of our multicenter prospective Clopidogrel Registry demonstrate lower efficacy of a 300-mg loading dose of clopidogrel at the time of stenting compared with pretreatment 6 to 24 hours before percutaneous coronary intervention on the 30-day composite clinical end point in the large unselected patient cohort, which suggests the benefit of clopidogrel pretreatment in all incoming patients with suspected significant coronary artery disease scheduled for coronary angiography.

Critical pathways using platelet testing to potentially optimize the use of oral antiplatelet therapy

Although monitoring anticoagulation is standard practice, monitoring antiplatelet therapy has not yet widely been adopted as a means of assessing antithrombotic response. However, bedside devices have recently become available that facilitate more rapid assessment of antithrombotic response, allowing this information to be developed into a critical pathway. Three major opportunities exist for oral antiplatelet therapy: (1) optimizing the dose of aspirin for long-term therapy; (2) optimizing the dose of clopidogrel, especially in percutaneous coronary intervention, acutely and during long-term therapy; and (3) evaluating the level of platelet inhibition before coronary artery bypass grafting or other major surgery. Several critical pathways are proposed that may assist clinicians in trying to ensure adequate platelet inhibition in these important clinical situations.

The clinical potential of a point-of-care assay to assess interindividual variability in platelet aggregation among patients taking clopidogrel

Clopidogrel is an important component of medical therapy for patients with acute coronary syndromes and those receiving coronary artery stents. Despite use of clopidogrel, a significant number of patients experience recurrent adverse ischemic events. Interindividual variability of platelet aggregation in response to clopidogrel may be an explanation for some of these recurrent events, and small trials have linked "clopidogrel resistance" as measured by platelet function tests to adverse events. Additionally, the degree of clopidogrel-induced platelet inhibition appears to be a factor determining bleeding risk at coronary artery bypass grafting. A point-of-care device that could accurately and rapidly measure the degree of platelet inhibition among patients taking clopidogrel could be clinically valuable. Such a device would have the potential to allow therapeutic decision-making based on the degree of platelet inhibition, especially for patients undergoing percutaneous coronary intervention or coronary artery bypass grafting.

A point-of-care assay to measure platelet aggregation in patients taking clopidogrel

Clopidogrel is an important component of medical therapy for patients with acute coronary syndromes and those receiving coronary stents. Despite the use of clopidogrel, a significant number of patients experience recurrent adverse ischemic events. Inter-individual variability of platelet aggregation in response to clopidogrel may provide an explanation for some of these recurrent events, and small trials have linked clopidogrel resistance, as measured by platelet function tests, to adverse events. The VerifyNowTM P2Y12 assay (Accumetrics, Inc., CA, USA) is a point-of-care device that can accurately and rapidly measure the degree of platelet inhibition in patients taking clopidogrel. This assay can identify patients with a poor response to clopidogrel, and could potentially lead to change in therapy.

Adding clopidogrel to aspirin improves outcome in ST-elevation myocardial infarction patients receiving fibrinolytic therapy

Acute coronary syndromes result from the rupture of an atherosclerotic plaque with superimposed thrombosis. In an ST-elevation myocardial infarction, the thrombus occludes the coronary vessel, leading to an abrupt decrease in myocardial perfusion. The focus of initial management is the timely restoration of flow in the infarct-related artery via fibrinolytic therapy or percutaneous coronary intervention. Adjunctive therapy aimed at inhibition of platelets and the coagulation cascade is critical to establish and maintain vessel patency. Clopidogrel, an oral antiplatelet agent, has recently been shown to offer significant clinical benefit in STEMI (ST-elevation myocardial infarction) and is a welcome addition to standard fibrinolytic therapy.