Is aspirin (acetylsalicylic acid) still a good choice for secondary prevention of ischemic heart disease (IHD) in a patient with a history of myocardial infarction (MI) and left bundle branch block (LBBB)?

Aspirin Use in Secondary Prevention for Patients with History of MI and LBBB

Aspirin remains a good choice for secondary prevention of ischemic heart disease in patients with a history of myocardial infarction (MI) and left bundle branch block (LBBB), as it significantly reduces the risk of serious vascular events by approximately 25% in patients with established cardiovascular disease. 1

Benefits of Aspirin in Secondary Prevention

• Aspirin is recommended as Class I (Level of Evidence: A) therapy for secondary prevention in patients with prior MI, regardless of the presence of LBBB 1
• In the chronic phase (>12 months) after myocardial infarction, aspirin is strongly recommended for secondary prevention (Class I, Level A) 1
• Low-dose aspirin (75-100 mg daily) is specifically recommended in patients with a previous MI or revascularization 1
• Aspirin therapy administered within the first 24 hours after acute STEMI results in a 23% relative risk reduction in 5-week vascular mortality 1

Evidence Supporting Long-term Aspirin Use

• Meta-analyses have confirmed the benefits of long-term aspirin therapy in patients at high risk of occlusive vascular events, including those with prior MI 1
• A meta-analysis of 16 secondary prevention trials (n=17,000 patients) demonstrated that aspirin allocation was associated with a 1.5% significantly lower risk of serious vascular events per year 1
• In patients with stable cardiovascular disease, low-dose aspirin therapy reduces the incidence of adverse cardiovascular events by 21% and all-cause mortality by 13% 2
• Treatment of 1000 patients for an average of 33 months would prevent 33 cardiovascular events, 12 nonfatal MIs, 25 nonfatal strokes, and 14 deaths 2

Dosing Considerations

• Following an initial loading dose of 162 to 325 mg of non-enteric-coated aspirin, an 81-mg daily dose is preferred to minimize bleeding risk 1
• Higher daily doses (900-1500 mg) are not more effective than lower doses (75-325 mg) 3
• For long-term treatment, doses of 75-100 mg daily are as effective as higher doses 4

LBBB Considerations

• The presence of LBBB alone does not contraindicate aspirin use for secondary prevention of IHD 1
• LBBB is not listed among the contraindications or exceptions for aspirin therapy in any of the major guidelines 1
• The benefits of aspirin in secondary prevention extend to all patients regardless of age, sex, history of hypertension, diabetes, or conduction abnormalities like LBBB 3

Potential Alternatives if Aspirin Cannot Be Used

• Clopidogrel 75 mg daily is recommended as a safe and effective alternative in patients with aspirin intolerance (Class I, Level A) 1
• The CAPRIE trial showed a slight superiority of clopidogrel over aspirin; the rate of serious vascular events was 5.32% per year with clopidogrel vs. 5.83% with aspirin 1

Bleeding Risk Considerations

• Aspirin therapy is associated with a small excess risk of major bleeding, with an odds ratio of 2.2 (95% CI, 1.4-3.4) 2
• For every 1000 patients treated for 33 months, approximately 9 major bleeding events may occur 2
• However, in secondary prevention, the benefits of aspirin therapy substantially exceed the bleeding risks 5

Conclusion

Based on the most recent and highest quality evidence, aspirin remains a good choice for secondary prevention of ischemic heart disease in patients with a history of MI and LBBB. The presence of LBBB alone does not alter the recommendation for aspirin therapy, as the benefits in reducing cardiovascular events and mortality outweigh the bleeding risks in patients with established cardiovascular disease.