I will be copying and pasting many different sources in this blog to help understand a stroke and the preferred method of prevention.
Let’s start off by defining a stroke as it applies to AF. The stroke most commonly caused by AF is an ischemic stroke. An ischemic stroke happens when an artery that carries blood to the brain gets clogged by a blood clot depriving the brain of oxygen. Without oxygen, the nerve cells in the brain die, and cannot be restored. This causes permanent disability in the parts of the body controlled by the impacted nerve cells. Ischemic strokes are the most common strokes as about 70–80 percent of strokes are due to blood clots. These clots can either form in the arteries going to the brain, or can come from some other part of the body. Most of the clots that come from other parts of the body are formed in the atria during atrial fibrillation. When the heart is overworked, weakened, and enlarged, it works even harder, which leaves more blood pooled in the atria. The atria quiver during atrial fibrillation, and thus don't completely empty, allowing blood clots to form.
In the above paragraph, I wrote that clots can form in two different ways.
One forms in the arteries and is normally caused by blood platelets “sticking” together and forming a blockage. This blockage can itself stop blood flow causing a stroke or portions can break off and block blood vessels causing a stroke.
The second type forms “in other parts of the body”. These are blood clots that can form anywhere in the body where blood is stagnant (pooled) and allows it to clot. When proper blood flow is restored, the clot can be pushed out into the system and cause a blockage resulting in a stroke. This is the form of stroke that is common with AF.
Now, Aspirin or Anticoagulant??? There is a lot of confusion about these.
Many years ago, numerous studies where done involving aspirin in stroke prevention. The most common results were that Aspirin has an antiplatelet effect by inhibiting the production of thromboxane, which under normal circumstances binds platelet molecules together to create a patch over damaged walls of blood vessels. Because the platelet patch can become too large and also block blood flow, locally and downstream, aspirin is also used long-term, at low doses to prevent strokes. The frequent use of aspirin at higher dosages can also cause a hemorrhagic stroke due to the lack of thromboxane.
So, it was published that to prevent a stroke, take an aspirin every day. And that is true for an ischemic stroke caused by blockage (sticky platelets).
Now the Anticoagulant…
An anticoagulant is a substance that prevents coagulation (clotting) of blood. Such substances occur naturally in leeches and blood-sucking insects. Anticoagulants reduce blood clotting. This prevents deep vein thrombosis, pulmonary embolism, myocardial infarction and stroke. Think of a cut on your hand. The blood comes to the surface and “pools” there and within a few minutes it will start to thicken and finally clot. This is similar to what can happen in the atria during an AF attack but the time it takes to clot on the surface is greatly decreased due to the presence of air. Many studies have shown that a clot can be formed within a few hours in the atria if the blood is allowed to pool. With an AF attack that lasts for 6 to 8 hours or longer the chances of a clot forming is vastly increased. An anticoagulant decreases the clotting factor of the blood which increases the time that it takes for a clot to form. This value or ratio is commonly measured in the INR (international normalized ratio). The normal desired range for INR is between 2 and 3 which basically means it will take 2 to 3 times the amount of time for the blood to clot. Since AF allows the blood to “pool” in the heart, this is the preferred type of stroke prevention.
So the overall result is that… While Aspirin has been found effective for stroke prevention caused by blockage (platelets sticking together), It has almost no effect in preventing a stroke caused by blood clotting. Prescribing Aspirin for a patient who has AF provides a false sense of safety against stroke unless there are other conditions which require aspirin. An anticoagulant is the only proven method to reduce risk of stroke for AF.
I am writing this because again today I have been in contact with another friend with AF who had a stroke 2 weeks ago. His doctor prescribed 75mg aspirin 2 years ago even though his chads2 score was a 2. And now at 45 years old and trying to overcome speech problems, loss of sight in one eye and loss of balance/coordination, He will never know if an anticoagulant may have kept this from happening.
I will finish this with a few facts about AF:
Atrial Fibrillation and Stroke Facts
•Each year, about 700,000 people have a stroke in the U.S., with about 500,000
being first attacks.
•About every 45 seconds someone in the U.S. has a stroke.
•Atrial fibrillation accounts for 15–20% of strokes in the U.S.
(105,000–140,000 per year).
•Atrial fibrillation patients have a five-fold increase in stroke risk.
•About 35% of atrial fibrillation patients will have a stroke during their lifetime.
•Atrial fibrillation increases with age, doubling each decade after age 55.
•Women account for 61 percent of U.S. stroke deaths.
•Women have a higher risk of death from atrial fibrillation.