When should aspirin (acetylsalicylic acid) be given to patients for cardiovascular protection?

When to Give Aspirin for Cardiovascular Protection

Aspirin should be given to all patients with established cardiovascular disease (secondary prevention) at 75-100 mg daily, while for primary prevention it should only be considered in patients at sufficiently high cardiovascular risk (≥10-20% 10-year risk) where benefits outweigh bleeding risks. 1

Secondary Prevention: Clear Indication for Aspirin

For patients with established cardiovascular disease, aspirin therapy is strongly recommended and the benefits far outweigh bleeding risks. 2, 1

Give aspirin 75-100 mg daily to patients with:

• Previous myocardial infarction - lifelong therapy after initial dual antiplatelet therapy period 1
• History of stroke or transient ischemic attack 1, 3
• Coronary revascularization (bypass surgery or angioplasty) 1, 3
• Significant obstructive coronary artery disease on imaging 1
• Peripheral arterial disease with symptoms 3
• Unstable or stable angina 4

The evidence for secondary prevention is robust, with aspirin reducing serious vascular events by approximately 25% across diverse high-risk populations. 4 The optimal dose is 75-100 mg daily (81 mg in the US), which provides full benefit with lower bleeding risk than higher doses. 1, 5

Primary Prevention: Risk-Based Decision Making

For primary prevention, aspirin should only be given when 10-year cardiovascular risk exceeds specific thresholds where benefits clearly outweigh bleeding harms.

High-Risk Patients Who Should Receive Aspirin:

Hypertensive patients aged <80 years with:

• 10-year cardiovascular disease risk ≥20% OR
• 10-year cardiovascular death risk ≥5% (SCORE model) 2
• Blood pressure must be controlled before starting aspirin 2

Diabetic patients aged ≥50 years with at least one additional major risk factor:

• Family history of premature ASCVD
• Hypertension
• Dyslipidemia
• Smoking
• Chronic kidney disease/albuminuria 2, 1

General population with:

• 10-year cardiovascular risk 6-10% or higher when benefits outweigh risks 1

The HOT trial demonstrated that in hypertensive patients with elevated baseline risk, aspirin prevented 3.1-3.3 cardiovascular events per 1,000 patient-years while causing only 1.0-1.4 major bleeds per 1,000 patient-years. 2

Patients Who Should NOT Receive Aspirin for Primary Prevention:

Do not give aspirin to:

• Patients aged <50 years with diabetes and no other major ASCVD risk factors - bleeding risk outweighs minimal benefit 2, 1
• Patients aged >70 years without established CVD - greater risk than benefit in this age group 2, 1
• Low-risk patients (10-year CVD risk <6-10%) - harm counterbalances benefits 2
• Patients aged <21 years - contraindicated due to Reye syndrome risk 2, 1
• Patients with uncontrolled hypertension - increased bleeding risk 1
• Active bleeding, bleeding disorders, or recent gastrointestinal bleeding 1

Critical Bleeding Risk Considerations

Aspirin increases major gastrointestinal bleeding by 2-4 events per 1,000 middle-aged persons over 5 years (4-12 per 1,000 in older persons). 2, 1 It may also increase hemorrhagic stroke risk by 0-2 per 1,000 persons over 5 years. 2, 1

Risk factors that increase bleeding complications:

• Age >70 years 2
• Concurrent use of NSAIDs or anticoagulants 1
• Anemia 2
• Renal disease 2
• History of peptic ulcer disease 3

The key clinical principle: In secondary prevention, cardiovascular events prevented far exceed bleeding events caused. In primary prevention, these numbers are roughly equal, making risk stratification essential. 2

Optimal Dosing

Use 75-100 mg daily (81 mg tablets in the US) for both primary and secondary prevention. 1, 5

• During acute MI: loading dose of 160-325 mg, then 75-150 mg daily 4
• Higher doses (>325 mg) increase bleeding without proportionally greater benefit 5
• Doses <75 mg have uncertain efficacy 4

Common Pitfalls to Avoid

Do not prescribe aspirin for primary prevention without:

1. Calculating actual 10-year cardiovascular risk using validated tools
2. Ensuring blood pressure is controlled in hypertensive patients 2
3. Assessing bleeding risk factors
4. Confirming aspirin is an adjunct to, not replacement for, lifestyle modification and other risk factor management 2, 4

Remember: Recent evidence shows aspirin's role in primary prevention has narrowed considerably, with most benefit limited to those at genuinely high cardiovascular risk where the absolute benefit exceeds the absolute bleeding harm. 2, 1