The Prevalence and Clinical Relevance of ASA Nonresponse After Cardiac Surgery: A Prospective Bicentric Study

Antiplatelet Resistance in Coronary Artery Bypass Grafting: A Systematic Review

Background

This systematic review examines the occurrence and implications of resistance to primary antiplatelet agents, aspirin and clopidogrel, often utilised in patients undergoing coronary artery bypass grafting (CABG), alongside the methodologies for assessment of such resistance.

Methods

An extensive literature search across various databases such as PubMed, MEDLINE via Ovid, Embase, and Cochrane CENTRAL until May 2024 was conducted to identify studies evaluating antiplatelet resistance in on-pump and off-pump CABG patients. Following quality assessment, only high-quality studies were incorporated into this review.

Results

This review included 19 studies with 3,915 patients, four of which were randomised controlled trials and 15 were observational studies. Aspirin resistance incidence ranged from 11.0% to 51.5%, while clopidogrel resistance was 22%. Antiplatelet resistance, assessed through a wide variety of methods, was associated with a 13 times increase in the risk of vein graft occlusion and increased rates of mortality, myocardial infarction, and target vessel revascularisation in the case of clopidogrel resistance. The effect of cardiopulmonary bypass on antiplatelet resistance remains ambiguous.

Conclusion

The academic literature lacks a standardised definition for antiplatelet resistance. Assessment methodologies greatly vary, leading to noninterchangeable outcomes. While aspirin resistance has a conflicting overall significant impact on adverse outcomes, clopidogrel resistance correlates with poorer clinical outcomes.

Unfractionated heparin reverses aspirin inhibition of platelets during coronary artery bypass graft surgery

Unfractionated heparin (UFH) is an effective antithrombotic during surgery but has known adverse effects, in particular on platelets. A marked increase in platelet responsiveness has previously been observed in patients within minutes of receiving UFH, despite adequate inhibition by aspirin prior to heparin. We studied this phenomenon in patients undergoing cardiac artery bypass grafting (n = 17) to determine whether the effects of heparin were systemic or platelet-specific. All patients' platelets were fully inhibited by aspirin prior to surgery, but within 3 min of receiving heparin spontaneous aggregation and responses to arachidonic acid (AA) and ADP increased significantly (p ≥ 0.0002), and activated platelets were found in the circulation. While there was no rise in thromboxane in the plasma following heparin, levels of the major platelet 12-lipoxygenase product, 12-HETE, rose significantly. Mixing experiments demonstrated that the changes caused by heparin resided primarily in the platelets, while addition of AA pathway inhibitors, and analysis of oxylipins provided evidence that, following heparin, aggregating platelets regained their ability to synthesise thromboxane. These findings highlight potentially unrecognised pro-thrombotic and pro-inflammatory changes during CABG surgery, and provide further evidence of adverse effects associated with UFH.

The Pre- and Postoperative Prevalence and Risk Factors of ASA Nonresponse in Vascular Surgery

Background

An antiplatelet therapy with acetylsalicylic acid (ASA) is prescribed in the prevention of cardiovascular events, but around 24% of ASA takers are resistant to the treatment.

Aim

In this prospective, observational cohort study, we aimed to identify the prevalence and risk factors of ASA nonresponse in patients who underwent vascular surgery.

Methods

The study was conducted in the University hospital in Frankfurt am Main. In total, 70 patients were pre-treated with 100 mg of ASA per day and underwent either elective carotid thromboendarterectomy, femoral thromboendarterectomy or endovascular aneurysm repair of the abdominal aorta. The platelet function was measured on the first preoperative and the second or fourth postoperative day with the multiple electrode aggregometry by in-vitro stimulation with arachidonic acid (ASPItest) and thrombin receptor activating peptide 6 (TRAPtest). The primary end point was the in-vitro induced platelet aggregation in the ASPItest. If the ASPItest amounted ≥400 AU × min, the patients were categorized as ASA nonresponders.

Results

The total prevalence of ASA nonresponse in our study was 20% preoperatively and 35.7% postoperatively (p = 0.005). As significant predictors for ASA nonresponse, we demonstrated the area under the aggregation curve in the TRAPtest preoperatively (p = 0.04) and postoperatively (p = 0.02), and the two comorbidities arterial hypertension (P < .001; rho 0.44) and diabetes mellitus (p = 0.04; rho 0.39), which are already well known to be associated with ASA nonresponse.

Conclusion

In conclusion, data of the study indicate a high incidence of perioperative, laboratory ASA nonresponse in patients undergoing vascular surgery.