Aspirin for Secondary Prevention of Coronary Artery Disease
For patients with established coronary artery disease, long-term low-dose aspirin (75-100 mg daily) or clopidogrel (75 mg daily) is strongly recommended as single antiplatelet therapy to reduce mortality and cardiovascular events. 1
Evidence for Aspirin in Secondary Prevention
Established CAD
- Aspirin 75-100 mg daily is recommended lifelong in patients with prior myocardial infarction (MI) or remote percutaneous coronary intervention (PCI) after an initial period of dual antiplatelet therapy (DAPT) 1
- Clopidogrel 75 mg daily is an equally effective alternative for patients who are intolerant or allergic to aspirin 1
- Single antiplatelet therapy is preferred over continued dual antiplatelet therapy after the first year post-acute coronary syndrome (ACS) 1
- Aspirin reduces risk of serious vascular events by approximately 25% in patients who have survived a prior occlusive vascular event 2
Dosing Considerations
- Low-dose aspirin (75-100 mg daily) is as effective as higher doses for long-term secondary prevention 2, 3
- After PCI, 81 mg of aspirin daily is reasonable in preference to higher maintenance doses 1
- For patients undergoing coronary artery bypass grafting (CABG), aspirin should be started within 6 hours after surgery to reduce saphenous vein graft closure, with dosing regimens of 100-325 mg daily for 1 year 1
Post-ACS and Stent Placement
- For patients with ACS who undergo PCI with stent placement, dual antiplatelet therapy with aspirin plus a P2Y12 inhibitor (ticagrelor, clopidogrel, or prasugrel) is recommended for up to 12 months 1
- After this initial period, single antiplatelet therapy with aspirin or clopidogrel is recommended over continued dual antiplatelet therapy 1
- For bare-metal stents, single antiplatelet therapy is recommended after the first month of dual antiplatelet therapy 4
- For drug-eluting stents, single antiplatelet therapy is recommended after 3-6 months of dual antiplatelet therapy 4
Clinical Considerations
Bleeding Risk
- There is a small excess of major bleeding among patients on aspirin, which is far outweighed by the magnitude of cardiovascular benefits 2
- Proton pump inhibitors may be effective in reducing the risk of gastrointestinal bleeding in patients on antithrombotic therapy, particularly those at increased risk 1
- Patients at increased risk of bleeding include the elderly, those with a history of GI bleeding or peptic disease, high alcohol consumption, chronic use of steroids or NSAIDs, or receiving a combination of antithrombotic drugs 1
Special Populations
- Recent evidence from the ADAPTABLE trial showed no significant sex-specific differences in the effectiveness and safety of different aspirin doses (81 mg vs 325 mg) for secondary prevention of ASCVD events 5
- For patients with aspirin hypersensitivity and CAD, desensitization protocols or alternative antiplatelet strategies may be necessary 6
Common Pitfalls to Avoid
- Continuing dual antiplatelet therapy beyond 12 months after ACS or stent placement without specific indications increases bleeding risk without additional benefit 4
- Using full-intensity oral anticoagulation in CAD patients without another indication (such as atrial fibrillation) should be avoided as it increases bleeding risk without additional benefit 1
- Inadequate dosing: doses below 75 mg daily may have less certain effectiveness for long-term treatment 2, 3
- Failure to consider drug interactions: some NSAIDs can block aspirin's access to the active site of COX-1, potentially reducing its effectiveness 1
In summary, the evidence strongly supports the use of low-dose aspirin (75-100 mg daily) or clopidogrel (75 mg daily) for secondary prevention in patients with established coronary artery disease, with the choice between agents depending on individual factors such as aspirin tolerance and comorbidities.