For a patient after coronary artery bypass grafting, should I prescribe aspirin alone or add a second antiplatelet agent, and if so, which drug, dose, and duration are recommended?

Dual Antiplatelet Therapy Post-CABG

For patients after isolated CABG, aspirin 81 mg daily should be started within 6 hours postoperatively and continued indefinitely; adding a P2Y12 inhibitor (clopidogrel 75 mg daily) for 12 months is mandatory if CABG was performed for acute coronary syndrome, and may be reasonable for 12 months in stable ischemic heart disease to improve vein graft patency. 1, 2

Clinical Context Determines P2Y12 Inhibitor Use

Post-CABG for Acute Coronary Syndrome (ACS)

• Resume P2Y12 inhibitor therapy postoperatively to complete a total of 12 months of dual antiplatelet therapy (DAPT) from the ACS event—this is a Class I recommendation. 1, 2
• Start the P2Y12 inhibitor as soon as safely possible after surgery, typically when chest tube drainage is ≤30 cc/hour for 2 hours. 2
• Ticagrelor 90 mg twice daily or prasugrel 10 mg daily are preferred over clopidogrel 75 mg daily for ACS patients when no contraindications exist. 2
• Never use prasugrel in patients with prior stroke or TIA—this is a Class III contraindication. 2
• If ticagrelor or prasugrel were used pre-CABG for ACS, resume the same agent postoperatively to complete 12 months total. 1, 2

Post-CABG for Stable Ischemic Heart Disease (SIHD)

• Adding clopidogrel 75 mg daily for 12 months may be reasonable (Class IIb recommendation) to improve saphenous vein graft patency when initiated early postoperatively. 1, 2
• This recommendation is based on observational data and propensity-matched analyses showing reduced mortality and improved graft patency with DAPT versus aspirin alone. 1
• The evidence quality is lower than for ACS patients, but the potential benefit for graft patency supports consideration in patients without high bleeding risk. 1, 2

Aspirin Dosing and Timing

• Start aspirin within 6 hours after CABG at doses ranging from 100-325 mg daily to reduce saphenous vein graft closure. 1
• Transition to low-dose aspirin 81 mg daily (acceptable range 75-100 mg) for long-term maintenance therapy. 1, 2
• Continue aspirin indefinitely in all post-CABG patients unless contraindicated. 1, 2
• Higher aspirin doses (>100 mg) increase bleeding risk without additional ischemic benefit when combined with P2Y12 inhibitors. 1

Duration Modifications Based on Bleeding Risk

High Bleeding Risk Patients

• In ACS patients who develop high bleeding risk postoperatively (e.g., need for oral anticoagulation, major intracranial surgery planned, or significant overt bleeding), discontinuation of P2Y12 inhibitor after 6 months may be reasonable. 1, 2
• High bleeding risk can be assessed using the PRECISE-DAPT score (≥25 indicates high risk). 2
• Continue aspirin monotherapy indefinitely even if P2Y12 inhibitor is stopped early. 2

Extended DAPT Beyond 12 Months

• In ACS patients who tolerated DAPT without bleeding complications and are not at high bleeding risk, continuation beyond 12 months may be reasonable. 1, 2
• This applies particularly to patients with high-risk features such as multivessel disease, left main involvement, or chronic kidney disease. 2

Evidence Supporting DAPT Post-CABG

Aspirin Monotherapy Evidence

• Early aspirin (324 mg started within 1 hour of CABG) reduced early vein graft occlusion from 6.2% to 1.6% (p=0.004) and late occlusion from 11.6% to 5.8% (p=0.01) at 1 year. 3
• Aspirin 325 mg once daily reduced 1-year graft occlusion from 22.6% to 13.2% (p=0.050), with greatest benefit in grafts to vessels ≤2.0 mm diameter. 4

DAPT Evidence

• Ticagrelor plus aspirin versus aspirin alone significantly increased saphenous vein graft patency at 1 year (88.7% vs 76.5%, difference 12.2%, p<0.001) in a randomized trial of 500 patients. 5
• Ticagrelor alone (without aspirin) showed no significant benefit over aspirin alone (82.8% vs 76.5%, p=0.10), emphasizing the importance of combination therapy. 5
• A smaller trial showed ticagrelor plus aspirin reduced the proportion of patients with graft occlusion (28.0% vs 48.3%, p=0.044) and was an independent predictor of graft patency on multivariable analysis (OR 0.25, p=0.03). 6
• Clopidogrel plus aspirin showed a trend toward reduced radial artery graft occlusion (10.5% vs 43.8%, p=0.05) in a pilot study, though overall graft occlusion rates were not significantly different. 7

Practical Management Algorithm

Step 1: Start aspirin within 6 hours post-CABG

• Use 100-325 mg initially, then transition to 81 mg daily for maintenance. 1

Step 2: Determine if P2Y12 inhibitor is indicated

• ACS indication for CABG? → YES: Resume P2Y12 inhibitor as soon as bleeding risk acceptable (typically when chest tube drainage ≤30 cc/hour × 2 hours). 2
• SIHD indication for CABG? → Consider adding clopidogrel 75 mg daily for vein graft patency benefit, especially if multiple vein grafts or grafts to small vessels. 1, 2

Step 3: Select P2Y12 inhibitor for ACS patients

• First choice: Ticagrelor 90 mg twice daily (preferred over clopidogrel). 2
• Alternative: Prasugrel 10 mg daily (if no prior stroke/TIA). 2
• If contraindications to above: Clopidogrel 75 mg daily. 1

Step 4: Plan duration

• ACS patients: 12 months total from ACS event (Class I). 1, 2
• SIHD patients: 12 months if using DAPT (Class IIb). 1, 2
• High bleeding risk: Consider stopping P2Y12 inhibitor at 6 months in ACS or not starting in SIHD. 1, 2

Common Pitfalls and Caveats

• Do not delay aspirin initiation—the benefit is greatest when started within 6 hours, and delays increase early graft occlusion risk. 1, 3
• Do not use prasugrel in patients with prior stroke or TIA—this is an absolute contraindication due to increased intracranial bleeding risk. 2
• Do not stop P2Y12 inhibitor prematurely in ACS patients without discussing with the patient's cardiologist—premature discontinuation markedly increases stent thrombosis and ischemic event risk. 2
• Minor bleeding is more common with DAPT (31.4% vs 2.9% with aspirin alone, p=0.003), but major bleeding rates are similar; counsel patients about bruising and minor bleeding. 6
• Consider proton pump inhibitors in patients with history of gastrointestinal bleeding or increased bleeding risk (advanced age, concomitant warfarin, NSAIDs, steroids). 1, 2
• The evidence for DAPT in SIHD post-CABG is weaker (Class IIb) than for ACS (Class I)—base the decision on individual patient factors including graft type, vessel size, and bleeding risk. 1, 2