Occurrence of Bleeding and Thrombosis During Antiplatelet Therapy in Non-cardiac Surgery

Occurrence of Bleeding and Thrombosis During Antiplatelet Therapy in Non-cardiac Surgery. A Prospective Observational Study (OBTAIN Study)

Research questions:

1. What is the absolute risk reduction for in-hospital major adverse cardiac events (MACE) associated with the use of dual anti-platelet therapy as compared with aspirin alone in this population?
2. What is the absolute risk increase for clinically significant bleeding during the same period associated with the use of dual anti-platelet therapy as compared with aspirin alone in this population?

In brief the design of the study is as follows:

• We will study patients undergoing non-cardiac surgery within four years of coronary stenting.
• We will record the anti-platelet agents taken by patients before, during and after surgery.
• We will record cardiac and bleeding events that occur whilst the patient is in hospital.
• We will use the statistical technique of propensity scoring to match patients who have similar risk factors and who received different anti-platelet regimens.
• We will compare the incidence of cardiac events and bleeding in the matched groups.

This study will compare the use of aspirin alone with dual antiplatelet therapy (i.e. aspirin and clopidogrel) in patients presenting for elective non-cardiac surgery who have undergone PCI with either bare metal stent or drug eluting stent placement in the four years prior to surgery. The absolute risk reduction in major adverse cardiac events (MACE) with dual antiplatelet therapy and the absolute risk increase for clinically significant bleeding events with dual therapy will be determined. This will allow the number needed to treat (NNT) for the prevention of MACE and the number needed to harm (NNH) for bleeding to be determined and the optimal antiplatelet therapy in this setting to be identified.

Inclusion Criteria:

• Patients undergoing non-cardiac surgery within four years of percutaneous coronary intervention (PCI) with the placement of a bare metal or drug eluting stent will be included in the study.

Exclusion Criteria:

• Patients maintained on anticoagulant therapy e.g. heparin infusion before and after surgery will be excluded. (Patients receiving prophylactic doses of heparin for prevention of thromboembolic events will be eligible for inclusion.)
• Patients receiving bridging therapy with full anticoagulant does of heparin or other drugs to compensate for the withdrawal of antiplatelet drugs will be excluded.
• Patients who are anticoagulated with warfarin (INR>1.5 at the time of surgery) will be excluded.
• Patients receiving full anticoagulation with heparin for a known recent a known thromboembolic event (APPT ratio > 1.5) be excluded. -