Aspirin for primary cardiovascular prophylaxis

What it is

By irreversibly inhibiting platelet function, aspirin reduces the risk of atherothrombosis but at the risk of bleeding, particularly in the gastrointestinal tract. At low dose it inhibits Cox1 and so prevents platelet activation. Low-dose aspirin therapy is recommended by the U.S. Preventive Services Task Force for the primary prevention of cardiovascular disease in patients 50-59 years of age who have a risk of CVD of 10% or more over 10 years. That is a USPSTF B recommendation, and it is the only age band with one. The age bands above and below it are not the same:

• 60-69 years: the decision to start aspirin should be based on individual considerations. USPSTF C recommendation.
• Younger than 50, or age 70 or older: the evidence is insufficient to assess the balance of benefits and harms.

How it is treated

Age and risk alone are not enough. Three further lines come with the recommendation, and they matter as much as the age band:

• A life expectancy of at least 10 years
• Willing to take daily aspirin for at least 10 years
• Not at increased risk for gastrointestinal bleeding

So the patient who is not willing to take daily aspirin for 10 years, or who is at increased risk for gastrointestinal bleeding, is not in the recommendation, however high the risk of CVD. Statins are beneficial for both primary and secondary prevention of cardiovascular disease, but the benefit is greater when the baseline risk is greater, and current guidelines would not support statin therapy for a patient with a 10-year ASCVD risk under 5%. Fish oil supplements have not proven to be useful for primary prevention of ASCVD. Niacin is no longer recommended for cardiovascular risk reduction, for lack of evidence of benefit. In antiphospholipid syndrome, primary thromboprophylaxis is low-dose aspirin therapy, and in pregnant individuals it is low-dose aspirin plus heparin. Aspirin also has to share the patient with an anticoagulant. Current guidelines recommend that patients with an ST-elevation myocardial infarction who also have atrial fibrillation take dual antiplatelet therapy such as aspirin plus clopidogrel and a vitamin K antagonist, with a goal INR of 2.0-3.0, and a patient already on a direct-acting oral anticoagulant continues it in addition to dual antiplatelet therapy. The duration of triple therapy should be as short as possible and aspirin can often be discontinued after 1-3 months, but a STEMI that occurred less than 2 weeks ago is too early for that, and triple therapy continues. Aspirin is well established for secondary prevention of ASCVD and is widely recommended for this indication, but recent studies have shown that in the modern era aspirin should not be used in the routine primary prevention of ASCVD due to lack of net benefit. Three recommendations follow there, based on meta-analysis and three recent trials: low-dose aspirin might be considered for primary prevention of ASCVD in select higher ASCVD adults aged 40-70 years who are not at increased bleeding risk; low-dose aspirin should not be administered on a routine basis for primary prevention of ASCVD among adults over 70 years; and low-dose aspirin should not be administered for primary prevention among adults at any age who are at increased bleeding risk. The age band differs as well: it is given as 40-70 years in one source and as 50-59 years in the Task Force recommendation, and both stand as written. The increased risk for bleeding that takes a patient out of the recommendation is wider than the gut alone. Aspirin is avoided in persons with increased risk of bleeding, including a history of GI bleeding or peptic ulcer disease, bleeding from other sites, age over 70 years, thrombocytopenia, coagulopathy, chronic kidney disease, and concurrent use of nonsteroidal anti-inflammatory drugs, steroids, and anticoagulants. Outside cardiovascular prevention, low dose aspirin from the first trimester is considered to reduce the risk of developing pre-eclampsia. That line belongs to a pregnancy protocol that also continues folic acid and penicillin prophylaxis and notes that SCD by itself scores 3, so it is not written for every pregnancy.

The two lines are also stated as rules. It is not recommended to start aspirin as routine in a pt above 70 yrs old. Low-dose aspirin might be considered for primary prevention of ASCVD in select higher ASCVD adults aged 40-70 years who are not at increased bleeding risk. So the man above 70 with no cardiovascular disease who asks in clinic whether to start daily low-dose aspirin is advised not to start it, and the reason is his age and not his risk.

The two preventions are defined beside them, which is what decides whether a risk is calculated at all. Primary prevention: no hx of CV events, and a risk assessment is needed. Secondary prevention: already has a cardiovascular event and seen by a specialist, and no need to do risk assessment. Beside it, any pt with DM should be on moderate intensity; any pt with HTN needs a risk assessment; a high intensity statin reduces LDL by 50% and a moderate intensity statin by 30%, and the dose is what makes the difference.