What are the aspirin (acetylsalicylic acid) therapy recommendations for patients with coronary artery disease (CAD) indicated by a computed tomography (CT) calcium score?

Aspirin Recommendations Based on CT Calcium Score

For patients with CAC ≥100, consider low-dose aspirin (75-100 mg daily) for primary prevention if bleeding risk is not elevated, as this threshold identifies individuals who derive net cardiovascular benefit that exceeds bleeding risk. 1

CAC Score-Based Aspirin Algorithm

CAC = 0

• Do not initiate aspirin unless ASCVD risk exceeds 20% 1
• Bleeding risk outweighs cardiovascular benefit in this population 1
• Aspirin is net harmful regardless of other risk factors when CAC = 0 1

CAC 1-99

• Generally avoid aspirin in this intermediate range 1
• Consider aspirin only if:
  • ASCVD 10-year risk ≥5% AND
  • Low bleeding risk (no history of GI bleeding, no anticoagulation, age <70) 2
• Most guidelines do not support routine aspirin for this CAC range 1

CAC ≥100

• Initiate aspirin 75-100 mg daily if no contraindications 1
• This recommendation is supported by:
  • American SCCT guidelines (consideration for all CAC >100) 1
  • NLA guidelines (aspirin 81 mg daily reasonable for CAC ≥100) 1
  • CSANZ guidelines (CAC 101-400 and >400 should receive preventive aspirin) 1
  • Chinese guidelines (CAC ≥100 may consider 75-100 mg daily) 1

CAC >400

• Strongly recommend aspirin as net benefit is substantial regardless of other risk factors 1
• Cardiovascular benefit clearly exceeds bleeding risk at this threshold 1

Critical Bleeding Risk Assessment

Before initiating aspirin based on CAC score, exclude high bleeding risk patients 1, 2:

• Absolute contraindications:

  • Active GI bleeding or peptic ulcer disease
  • History of intracranial hemorrhage
  • Severe thrombocytopenia
  • Known aspirin allergy/hypersensitivity 3

• Relative contraindications (aspirin net harmful):

  • ASCVD risk <5% regardless of CAC score 1
  • Concurrent anticoagulation therapy
  • History of significant GI bleeding
  • Uncontrolled hypertension
  • Age >70 with additional bleeding risk factors 2

Age and Risk Considerations

• Age 40-70 years: Primary target population for CAC-guided aspirin therapy 1
• Age >70 years: Exercise greater caution; bleeding risk increases substantially and may outweigh benefit even with CAC ≥100 1
• ASCVD risk ≥5%: Required threshold for considering aspirin when CAC ≥100 2

Dosing Recommendations

• Primary prevention dose: 75-100 mg daily (or 81 mg in US formulations) 1
• No loading dose required for stable CAD/primary prevention 4
• ESC alternative: 70 mg daily acceptable 1

Alternative Antiplatelet Strategy

For patients with aspirin intolerance or hypersensitivity but CAC ≥100:

• Clopidogrel 75 mg daily is a safe and effective alternative (Class I, Level A recommendation) 1, 4
• No loading dose needed for chronic stable disease 4
• Consider proton pump inhibitor if GI intolerance was reason for aspirin discontinuation 1, 4

Monitoring and Adjunctive Therapy

• Add proton pump inhibitor for patients at increased GI bleeding risk receiving aspirin 1
• Avoid calcium channel blockers when possible, as they may reduce aspirin effectiveness and increase aspirin resistance (OR 1.72 for high on-aspirin platelet reactivity) 5
• Reassess bleeding risk if initiating anticoagulation or other antithrombotic agents 1

Important Caveats

The evidence shows CAC scoring provides superior risk stratification compared to traditional ASCVD risk scores alone for aspirin allocation 1. However, bleeding risk assessment remains paramount - even with CAC >400, aspirin causes net harm in patients with elevated bleeding risk 1, 2. The strongest evidence supports a CAC threshold of ≥100 as the decision point where cardiovascular benefit exceeds bleeding risk in appropriately selected patients 1.

Note that ACC/AHA and ESC primary prevention guidelines do not explicitly incorporate CAC thresholds for aspirin decisions, but specialty societies (SCCT, NLA, CSANZ) provide more definitive CAC-based recommendations 1.