Guidelines and recommendations have moved away from routine use for primary prevention. Here’s why.
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Many people take baby Aspirin. They’ve never had a heart attack or stroke or stent or any cardiac problem in the past but they take a daily Aspirin because they heard somewhere, from someone, that they should. Except, they shouldn’t. And a shockingly large number, nearly a third of older adults in the U.S., are taking Aspirin when they shouldn’t be.
It’s a surprising thing for many people to hear, but the risks of a daily Aspirin can sometimes outweigh the benefits. In 1988, the ISIS-2 trial in The Lancet demonstrated that giving Aspirin to someone having a heart attack saves lives. It has remained a cornerstone of cardiac treatment ever since. But the remarkable benefits of Aspirin in this context were soon expanded from secondary prevention (treating people who already have the disease to prevent recurrent events) to primary prevention (treating people who are disease-free to prevent the disease from forming).
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The secondary prevention of cardiovascular disease is very clear. If you’ve had a heart attack, stroke, cardiac stent, bypass surgery or have any form of pre-existing cardiovascular disease then you should probably be on Aspirin. There is a small caveat that if you are taking another blood thinner for another reason, that may supersede the need for Aspirin and combining them might unnecessarily increase your risk of bleeding. But individualized nuance aside, anyone with pre-existing heart disease should be on Aspirin, or something comparable, unless there is some specific issue like bleeding which precludes its use.
For primary prevention though, the benefits of Aspirin are less clear. Older studies from the 1980s like the Physicians Health Study in The New England Journal of Medicine did show a benefit to prophylactic Aspirin use. But more recent analyses have not, with a fairly small cardiovascular benefit being offset by a higher risk of bleeding.
The reason for this flip-flop is probably easy to explain. People were sicker 40 years ago. People smoked more, they walked around with blood pressures of over 150, there were no good treatments for high cholesterol, and many of the medications we now use to treat diabetes didn’t exist. Basically, Aspirin was useful because very little else was available to blunt that increased cardiovascular risk.
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Now, things are better. We are much better at controlling blood pressure, treating diabetes and lowering cholesterol. Not to mention that fewer people smoke these days. Which means there is less residual cardiac risk out there in the population for Aspirin to have much of an effect.
And here lies an important point: It’s not that Aspirin is ineffective at preventing cardiovascular events. It still inhibits the platelets that are responsible for the arterial blockages that cause heart attacks and strokes. But the magnitude of the benefit is too small to be meaningful, especially when you consider that it can also increase the risk of serious bleeding.
What’s surprising is that high Aspirin use has persisted despite the fact that guidelines and recommendations have moved away from routine Aspirin use for primary prevention. The American College of Cardiology and American Heart Association guidelines do not recommend Aspirin for prevention, and the U.S. Preventive Services Task Force recommends against its routine use in adults over 60.
Since the guidelines changed several years ago, Aspirin use has decreased, which suggests more physicians are recommending Aspirin discontinuation. And yet with nearly a third of older adults in the U.S. still on Aspirin for primary prevention despite recommendations to the contrary, it suggests that more work on deprescribing needs to be done. But around five per cent of the population was taking Aspirin on their own without medical advice, so it would seem that many patients are still relying on echoes of old advice. We don’t often have similar large cohort studies in Canada, but these guidelines and trends tend to be common for both countries.
As with all things, Aspirin is beneficial when used by the right patients. But patients with no history of heart disease and no high risk features are the wrong patients in this case.
Christopher Labos is a Montreal physician, co-host of the Body of Evidence podcast, and author of Does Coffee Cause Cancer?
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