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The Princeton Longevity Center Medical News

Preventing Heart Attacks With Aspirin

By: David A Fein, MD
Medical Director

Taking a daily aspirin tablet can dramatically lower your heart attack risk.  But that does not mean that everyone should be taking a daily aspirin.  For those who are at low risk for a heart attack daily aspirin use may actually increase their risk of serious illness.  At the same time, in as many as one-quarter of those who are at high risk for heart attacks and have been told to take a daily aspirin, it may not be working at all.

Aspirin’s ability to prevent heart attacks and strokes is directly tied to its “blood thinning” effects.  Actually, aspirin does not make the blood “thinner”.  Instead, it inhibits the ability of platelets to form a clot.  People who are taking aspirin, for any reason, may notice that when they cut themselves it takes longer for the bleeding to stop because the aspirin has interfered with platelet function.

Most heart attacks are caused by clots.  Modern medicine tends to focus on narrowing of the arteries as the main problem in need of treatment.  Narrowed arteries can cause chest pain with exertion and other symptoms but most heart attacks do not occur at those spots.  Rather than a gradual narrowing of the artery, most heart attacks occur when the surface of a relatively mild plaque in the artery wall splits open.  This exposes the inside of the plaque to the bloodstream and some of the substances inside the plaque cause a blood clot to form at that spot.  If a very small clot forms and seals the rupture it may not interefere with bloodflow through the artery.  When a larger clot occurs it can completely occlude the flow of blood through the artery and a heart attack ensues. 

The idea behind taking a daily aspirin is that inhibiting clot formation makes it more likely you will form a small clot rather than a large one when plaque rupture occurs.  In general it appears that this effect can reduce the risk of heart attacks by about 30%.

On the other hand, aspirin can have potentially dangerous side effects.  It can irritate the lining of the intestinal tract and cause ulcers.  If those ulcers start to bleed, the anti-platelet effect can make that bleeding much more dangerous.  This is estimated to happen in as many as 1% per year of the people who take daily aspirin.  Aspirin can also increase the risk of a hemorrhagic stroke due to bleeding into the brain.  This may happen to about 1 person per year out of every 1000 who take aspirin daily and can be a devastating event.

While these events are not common, they are potentially very dangerous.  So aspirin really makes sense only for those where the reduction in heart attack risk is greater than the risk of side effects.  Unless your heart attack risk is at least 2-3 % per year, taking a daily aspirin may actually increase your risk of stroke or intestinal bleeding more than it lowers your heart attack risk. 
For those who are at high risk for heart attacks, aspirin can be a life-saver.  But, in about 25% of the people who take a daily aspirin they do not get the protection they are expecting.  This phenomenon is known as “aspirin resistance”.  In “aspirin resistant” patients, the usual recommended dose of one baby aspirin (81 mg,) per day does not adequately block the ability of the platelets to clot.  Without this anti-platelet effect, they get little or no reduction in their heart attack risk.

Aspirin blocks production of a chemical called Thromboxane.  A simple and inexpensive urine test, from AspirinWorks and available at Princeton Longevity Center, can measure the level of one of the metabolites of Thromboxane.  This test can determine whether your daily aspirin dose is effective at protecting you against blood clots and lowering your heart attack risk.  If the urine test shows the aspirin is not having the desired effect your doctor can opt to increase the daily dosage.  In some patients even higher doses of aspirin do not offer adequate protection.  In these patients prescription medications, such as Plavix, are available to block clot formation by a different mechanism.

Taking a daily aspirin can be one of the most effective tools available to prevent heart attacks.  But taking a daily aspirin without knowing whether or not you have plaque in your arteries may actually increase your health risks if you don’t have plaque in the first place.  If you are at high risk and could benefit from aspirin therapy then it is very important to determine if you need a higher dose or don’t respond to aspirin at all. 

We recommend that men over 40 and women over 50 check their arteries with a Coronary Calcium Heart Scan.  If your score is over 100 you are at elevated risk and should consider anti-clotting therapy with aspirin.  If you need to be on daily aspirin, you should have the AspirinWorks urine test done to determine your optimum dosage or the need for other medication.

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