Different perspective on ASA use

We read with interest the article by Ms Truong in the November issue of Canadian Family Physician on low-dose acetylsalicylic acid (ASA) for primary prevention of cardiovascular disease.¹ While we agree with Ms Truong’s first suggestion that ASA should not routinely be recommended for the primary prevention of cardiovascular disease, we have different perspectives on the other 2 questions that she addresses.

When should we offer ASA for primary prevention?

Ms Truong suggests that ASA should be offered when the benefits outweigh the risks, and suggests identifying “high risk” patients based upon the presence of various risk factors (eg, men older than 50 years of age). Our approach is to use cardiovascular risk calculators to estimate an individual’s risk of a cardiovascular event to avoid arbitrarily categorizing individuals as high, moderate, or low risk. An excellent website that has 3 such calculators is http://cvdcalculator.com. The calculator that we use most often is the ASCVD (atherosclerotic cardiovascular disease) calculator, which calculates the 10-year risk of heart attack, stroke, and cardiovascular death. The 2009 Antiplatelet Trialists’ Collaboration patient-level meta-analysis suggests that ASA reduces the risk of a first serious cardiovascular event by approximately 10%.² In the example of a 50-year-old man who is subjectively classified as high risk based upon sex and age alone, it is possible that his 10-year risk of heart attack, stroke, or cardiovascular death is only 1% when using the ASCVD calculator. The use of ASA every day for 10 years in this individual might lower that risk by about 0.1%, an amount likely considered unimportant by most clinicians and patients. By using risk calculators, and knowing the estimated risk reductions of various interventions, health care professionals can have discussions with patients about specific benefits and harms of various interventions in the spirit of shared decision making.

Should we stop ASA in patients who have been using it for primary prevention for many years?

Ms Truong highlights a theoretical concern of provoking a hypercoagulable state when discontinuing ASA. To support this, she cites 3 sources: 1) a review article, 2) a retrospective case-control study in patients taking ASA for the secondary prevention of cardiovascular events, and 3) a rapid-response opinion to the second citation that did not provide any new information. In our own search of the literature, we could not find any credible information that suggested an increased risk of cardiovascular events in patients stopping ASA when it was being used for primary prevention. We believe this is very important to note, as we do not believe that clinicians should hesitate to stop ASA when there is no clear indication for its use.

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