Impact of Hybrid Coronary Revascularization on Antiplatelet Therapy

Objective:

The effect of antiplatelet therapy is impaired among patients, who recently underwent on-pump coronary artery bypass grafting. The impact of hybrid coronary revascularization using minimal invasive surgical techniques on the antiplatelet effect of aspirin and clopidogrel remains unclear.

We hypothesize that hybrid coronary revascularization is associated with a transiently reduced antiplatelet effect of aspirin and clopidogrel. We hypothesize that the reduced antiplatelet effect of aspirin and clopidogrel could be explained by increased platelet turnover with an increased fraction of immature platelets in the peripheral blood. Furthermore, we hypothesize that the reduced antiplatelet effect is associated with increased inflammatory markers in the early postoperative phase. We hypothesize, that high platelet aggregation prior to the intervention is associated with reduced effect of antiplatelet therapy following hybrid coronary revascularization.

Methods:

40 patients with coronary artery disease will be enrolled in this prospective cohort study (recruited from a prospective pilot study conducted to assess feasibility and safety of hybrid coronary revascularization combining minimally invasive off-pump coronary artery bypass grafting through an inferior J-hemisternotomy (JOPCAB) with percutaneous coronary intervention - Clinicaltrials.gov identifier: NCT01496664). Demographics and medical history are documented preoperatively. The predicted mortality is assessed by means of the logistic European System for Cardiac Operative Risk Evaluation (EuroSCORE) I. Adverse cardiovascular events are recorded prospectively, including graft dysfunction, myocardial infarction, stroke, and pulmonary embolism.

Six blood samples are obtained from each patient:

• Pre-OP: in the outpatient setting while patients were on aspirin 75 mg daily
• Baseline: in the morning prior to surgery after eight to ten days of aspirin discontinuation (off-aspirin)
• Post-OP: on the first postoperative day when aspirin had been resumed
• Pre-PCI: on the day prior to PCI
• Post-PCI: on the first day after PCI following initiation of dual antiplatelet therapy
• 1-year follow-up: when patients were still on maintenance aspirin 75 mg and clopidogrel 75 mg Platelet function analyses are performed using Multiplate® Analyzer (Roche, Roche Diagnostics, Mannheim, Germany), VerifyNow® Aspirin, and VerifyNow® P2Y12 (Accumetrics Inc., San Diego, CA, USA). For Multiplate® Analyzer, arachidonic acid (1.0 mM) and adenosine diphosphate (6.4 and 20 uM) are used as agonists.

Complete blood counts, including immature platelet fraction (IPF), immature platelet count (IPC), and mean platelet volume (MPV), are performed using a Sysmex XE-5000 haematology analyzer (Sysmex, Kobe, Japan) with upgraded software (XE IPF Master, Sysmex) enabling flow cytometric detection of the IPF. Enzyme-linked immunosorbent assays are used according to the manufacturers' instructions to measure serum thromboxane B2 (Cayman Chemical, Ann Arbor, MI, USA) and thrombopoietin (R&D Systems Europe, Abingdon, UK). Plasma C-reactive protein was measured by immunoprecipitation using the Cobas® 6000 (Roche, Basel, Switzerland). Von Willebrand factor (antigen) and coagulation factor VIII (functional) are measured using the ACL TOP (ILS Laboratories, Bedford, MA, USA).

Inclusion criteria

• symptomatic multivessel coronary artery disease
• treatment with non-enteric coated aspirin 75 mg once daily

Exclusion criteria

• aspirin or clopidogrel intolerance
• conditions prohibitive of aspirin discontinuation prior to surgery
• use of anticoagulants or any drugs other than aspirin known to affect platelet function
• use of immunosuppressive drugs
• platelet count <100 or >450 x 109/l
• inability to give informed consent