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Aspirin has long been part of our armamentarium for the acute treatment of heart attacks. In addition to its more familiar analgesic properties aspirin helps keep clogged arteries open by blocking the action of platelets, key players in the blood clotting cascade that ensues during a heart attack or stroke. As a result people that present to clinic or the ER with chest pain are often given an aspirin right when they get in the door. Aspirin has also become a standard part of secondary heart attack and stroke prevention - that is in preventing a second heart attack or stroke in people who have already had one. More recently there has been great interest in aspirin in people who have never had a cardiovascular event but are at greater risk for having one - for example, a 58 year old male smoker who has poorly controlled blood pressure. While studies vary, the evidence suggests that in the right people aspirin can prevent up to 50 percent of first heart attacks. Similar data shows that in the right people aspirin also prevents first strokes. Hence I like to say, "An aspirin a day keeps the heart attacks and strokes away."
But from there it gets tricky. Knowing who the "right people" are isn't as straightforward as one would hope. Aspirin is effective in preventing heart attacks and strokes in some people and not others. What's more, the people that aspirin prevents heart attacks in are not necessarily the same people in which it prevents strokes. At the same time, there are serious risks to aspirin therapy. Because it inhibits blood clotting, aspirin increases the risk of gastrointestinal bleeding and certain types of strokes called hemorrhagic strokes. Thus there are some people that aspirin would benefit but for whom the risks of aspirin therapy are too great. So the question is how do we know if someone is a good candidate for aspirin? How do we identify the patients in whom the benefits of aspirin therapy are likely to outweigh the harms?
The U.S. Preventive Services Task Force (USPSTF) recently put forth the new recommendations to help doctors answer that very question (published March 2009). Their guidelines recommend aspirin for:
- Men ages 45 to 79 years when the benefits of reducing heart attacks outweighs the potential harms of gastrointestinal bleeding.
- Women ages 55 to 79 years when the benefits of reducing ischemic strokes outweighs the potential harms of gastrointestinal bleeding.
These guidelines reflect the USPSTF's conclusion that aspirin only reduces heart attacks in men and only reduces strokes in women. For women younger than 55 years and men younger than 45 years they recommend against aspirin for primary prevention. For men and women 80 years or older they conclude that the data are insufficient to recommend for or against aspirin.
While the guidelines are helpful they are not entirely satisfying. On one level they give us very definitive guidance: aspirin should primarily be considered in men ages 45 to 79 and women ages 55 to 79. But on another they leave much room for ambiguity: for patients in these ages ranges how do we know when the benefits of aspirin outweigh the harms? In the supporting documents, the USPSTF gives us further guidance based on a patient's Framingham risk score (a validated method for estimating a patient's 10-year risk of a cardiovascular event using clinical information such as age, gender, smoking status, and blood pressure, see here). For a given gender and age range, they provide cutoff Framingham risk scores above which the benefits of aspirin are likely to exceed the risks. For example, for the average male patient ages 60 to 69 if the 10-year risk of heart attack is greater than 9 percent the benefits of aspirin exceed the harms. This assessment requires two steps: one, using established "risk calculators" to determine a patient's 10-year risk score (available online or as single-page worksheets) and two, determining if a patient is at higher risk for gastrointestinal bleeding (e.g. chronic NSAID use, history of stomach ulcers). Nevermind if these details are overwhelming - let's just say that making these determinations is not at all straightforward and even for doctors can be confusing, not to mention difficult to implement in a 10-minute office visit.
If that was not complicated enough, add to the mix the fact that not all doctors agree with the U.S. Preventive Services Task Force. The American Heart Association (AHA) puts forth recommendations on aspirin for primary prevention that differ substantially from the USPSTF guidelines. For one they conclude that in women aspirin canprevent heart attacks, in addition to preventing strokes. In fact, they recommend aspirin to prevent heart attacks in all women ages 65 and older provided that their blood pressure is controlled and they are not at increased risk of gastrointestinal bleeding. In women under age 65 they recommend aspirin to prevent heart attacks in high-risk women who are not at increased risk of gastrointestinal bleeding, including women with diabetes, end-stage kidney disease, or a history of atherosclerotic disease. Why these guidelines differ so vastly from the USPSTF guidelines in another discussion in itself but it leaves doctors at a loss for knowing which guidelines to trust.
Taking these ambiguities into consideration and figuring out how to apply them to the patient in front of me is challenging and at times frustrating. I know that aspirin can help some of my patients reduce their chances of one day having a heart attack or stroke. Both of these diseases are scary enough that I want to do the best I can to prevent them. On the other hand, I don't want to overdo it. Gastrointestinal bleeding is a serious problem that in the worst cases requires blood transfusion, endoscopic procedures, and even surgery. At the same time, each additional medication I prescribe my patients is a burden that complicates their medical regimen that much more. So where does all this leave me and my patients? At the time of this writing I don't have all the answers. I still don't know which guidelines are the best ones to use. I don't know how to reliably estimate the benefits and harms of aspirin, especially in women. And I don't know how to decide who are the "right people" to prescribe aspirin to. What I do know is that there are patients out there who may one day suffer from a heart attack or stroke that could have been safely prevented with aspirin. If I'm honest with myself, I know that some of my patients are among them. The only question is which ones.
Copyright Shantanu Nundy, M.D.
If you enjoyed this post, please visit Dr. Nundy's web site at http://beyondapples.org or read his book, Stay Healthy At Every Age.
