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Hundreds of millions of adults who have passed the age of 40 are advised to take a "baby Aspirin" (an 81 mg dose in the US, a 75 mg dose in most of the rest of the world) every day to prevent heart attacks. Sometimes, however, taking Aspirin every day is not a good idea.
Aspirin and Heart Attack Prevention
Aspirin acts as a mild anticoagulant, or "blood thinner." When you bleed, specialized blood cells known as platelets, build up at the site of the wound. These blood cells accumulate to plug the leak so that blood loss is minimal.
The muscle cells in this part of the heart go into hibernation, ceasing to function, and typically "burn out" when the heart is reperfused, when the blood clot eventually breaks up.
Aspirin in low doses prevents platelets from sticking together to form clots. This reduces the risk of heart attack or stroke, but increases the risk of bleeding. The effects of Aspirin used by itself are usually so mild, however, that the benefit to the heart is thought to outweigh the increased risk of bleeding, especially in people who are known already to have coronary artery disease or who have already had a heart attack.
The Special Case of Atrial Fibrillation
Blood clots don't always form at the sites of injury or in the heart. Blood clots can also form in the brain, causing stroke. And one of the most common causes of blood clots that travel to the brain is an abnormal heart rhythm known as atrial fibrillation.
Atrial fibrillation, known colloquially as A-fib, is an unusually rapid rhythm in the upper chambers of the heart, known as the atria. The heart's rhythm is paced by electrical signals sent out by a nerve known as the sinoatrial node. In a healthy heart, the electrical impulse travels from the sinoatrial node from cell to cell from top to bottom of the heart so that the whole heart beats with a regular rhythm.
In atrial fibrillation, nerves in the pulmonary veins, which bring oxygenated blood back from the lungs to the heart to be pumped throughout the rest of the body, send out "noisy" impulses that cause extra beats in the two upper chambers of the heart. The heartbeat become more rapid, and each beat has less "oomph" to circulate blood through the body.
See Also: Atrial Fibrillation Treatment
As a form of atrial fibrillation treatment people who have A-fib are prescribed anticoagulants such as Plavix (clopidogrel), Coumadin (warfarin), Pradaxa (dabigatran), Xarelto (rivaroxaban), and others. When people who have A-fib are started on Plavix, they usually also are prescribed a baby Aspirin a day. And sometimes patients can't or won't take a prescription anticoagulant and are given just Aspirin. Recent research from Sweden finds that Aspirin alone is not sufficient to prevent stroke.