Preventing further heart attacks

Aspirin is taken daily following a heart attack to reduce the risk of another heart attack. (Preventing further heart attacks is called secondary prevention, while preventing the first heart attack is called primary prevention). The ideal daily dose of aspirin for secondary prevention has not been established. Some doctors recommend 160 mg; others recommend 81 mg.

The reason for this difference has to do with aspirin's occasional long-term side effect of bleeding (for example from stomach ulcers). Even though the risk of major bleeding with long-term, moderate dose aspirin (325 mg/day) is low (less than 1%), this risk can be lowered slightly by using an even lower dose (160 or 81 mg/day).

Aspirin also benefits patients with forms of coronary heart disease other than an acute heart attack. Aspirin has been shown to reduce heart attacks and improve survival in the following patients:

• Aspirin improves survival among patients with unstable angina. Patients with unstable angina experience chest pains at rest or with minimal exertion. These patients have critically narrowed coronary arteries and are at imminent risk of having a heart attacks
  
• Aspirin improves survival among patients with stable exertional angina. (These are patients who experience chest pain only with exertion.)
  
• Aspirin prevents formation of blood clots at the site of the PTCA (see below).
  
• Aspirin prevents the formation of blood clots that can occlude surgical bypass grafts. (Occlusion of bypass grafts can lead to heart attacks.)
  
• Aspirin in low doses (81 mg/day) has been shown to prevent first heart attacks (primary prevention)
  

The thienopyridines

The thienopyridines such as ticlopidine (Ticlid) and clopidogrel (Plavix) inhibit the ADP receptor on the surface of platelets. Inhibiting the ADP receptors on the platelets prevent the platelets from aggregating and causing blood clots to form. The theinopyridines are more potent anti-platelet agents than aspirin. Clopidogrel (Plavix) is used far more commonly than ticlopidine (Ticlid) because ticlopidine can, in rare instances, cause low platelet and/or white blood cell counts. Clopidogrel plays an important role in the treatment of heart attacks and is used in the following situations:

• Clopidogrel is used instead of aspirin in patients who have an allergy to aspirin.
  
• Clopidogrel often is given together with aspirin in treating heart attacks. Studies have shown that the combination of aspirin and clopidogrel is more effective than aspirin alone in improving survival and limiting damage to heart muscle among patients with heart attacks.
  
• Clopidogrel is given together with aspirin to patients undergoing PTCA with or without coronary stenting (see later discussion). Studies have shown that the combination of aspirin and clopidogrel is more effective than aspirin alone in preventing formation of blood clots that can re-occlude the coronary artery unblocked by PTCA and in preventing blood clots within recently placed stents.