AF Association
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Stroke Risk, Aspirin or Anticoagulant?

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.

First Aspirin….

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.


14 Replies

Hi Tim

Thank you for a well written and researched piece of work, there is so much work to do to educate not just us, but medical professionals.

And I am really sorry to hear about your friend, who appears to have had a preventable stroke.

I have a question, I, like others, I am on warfarin and 75mg aspirin, your research appears to confirm what I was told, in that they do two different jobs, but of course it would appear that aspirin has more side effects than warfarin with it's potential to " cause a hemorrhagic stroke".

There appears to be no question whatsoever that aspirin alone would not be adequate prevention. But recognising that every decision is a balance between risk and reward, what is the correct balance between the two? and should they be taken together?

I am still a little confused about this and would appreciate anyone's thoughts or comments.



Hi Tim,

That's a great summary, well done.

Hi Ian,

It can be dangerous to give aspirin and warfarin together, they can increase the risk of a hemorrhagic stroke with no reduction in stroke risk through a blood clot. However there may be other reasons you were given the aspirin, e.g. due to heart blockages. If you don't have other risks which aspirin would help prevent, then I would query this with your doctor. Warfarin alone compared with warfarin/aspirin is safer for most people.

From what I've read, warfarin alone is safer than aspirin alone as long as you can keep INR in the 2-3 range. That is critical.



Thanks Mark

Yes I have a high calcium score, although the CT scan showed no significant blockages, and it may well be for that reason that the aspirin is given. I'm not seeing my cardio for six months now. Following the failed cardioversion, he has said that without any other symptons, and a score of 0 on both CHADS and CHADS-Vacs (spelling?) then firstly the warfarin is optional (I have chosen to stay on) and that he wanted me on statins for prevention, and switched me from bisoprolol to diltiazem (good move much less tired) but said I could wean myself off those if I can demonstrate stable low blood pressure and heart rate.

Personally, I am still left with persistent (permament) A Fib, and I can't help feeling that it's a case of not sufficient symptoms to treat, but I can't help but worry about the damage the A Fib is doing, and that eventually they will have to treat anyway, so why not now?

Anyway thanks for the feedback, much appreciated



Thanks, Ian. I guess your options are to either have an ablation or remain on your current regime. If you're going to have an ablation then it's probably better sooner rather than later as the longer you're in persistent AF the harder it'll be to convert back. There are new options coming out which increase the chance of success, I think there's a jacket for much increased accuracy of mapping, which I understand gives particularly good results with persistent AF. But this is new technology and I'm not sure anyone's using it in the UK currently.

Staying on drugs is a reasonable option as long as you stop the heart rate going too high (which would lead to heart failure). Diltiazem is good for that. I also found the Dilt much better than the beta blockers when I had AF (since ablated).



Numerous articles say that if your CHA2DS2-VASc score is 1 you may consider an antiplatelet regimen (aspirin) or an anticoagulant. With a score of 2 you should be treated with an anticoagulant. There are studies showing that aspirin is ineffective in preventing strokes resulting from AFib. My EP and Cardiio both told be to stop taking aspirin when I started taking Xarelto (rivaroxaban) because of increased bleeding risk. I'm not sure about the bleeding risk of aspirin with warfarin.



Hi Tim, another great piece of work.

One thing I would add is that aspirin can also cause gastro-intestinal bleeds. Since many GPs in UK seem terrified of these and cite them as a reason for NOT prescribing warfarin it seems quite bizarre that they continue to prescribe aspirin.. Despite all the knowledge available, rolling it out to the primary care sector staffed in many cases with older doctors is not easy.

Some more facts.

The AF related strokes form 80% of the least recoverable events.

3000 deaths a year could be avoided in UK if all those at risk patients were anti coagulated.

UK has one of the lowest percentage of at risk patients actually on anticoagulants in Europe. (I think Latvia may be behind us).

Keep up the good work.



Thank you all for the comments... This is a subject that is near and dear to my heart. I speak to so many who honestly believe that an aspirin protects them from stroke caused by their AF and this is just not true. Most I speak to got this from their Drs which makes me question the understanding of the medical world. How many "learned" their trade 20 years ago and have not studied since then not realizing that things change in the medical world every day?

God question Ian, I often question the use of both anticoagulants and aspirin. It would seem that the proper use of an anticoaugulant would in effect also help the build up of platelets due to the thinning of the blood. And with the knowledge that aspirin causes, as Bob said, gastro-intestinal bleeds also "brain bleeds" and in combination with an anticoagulant could be a dangerous pair. I would think that choosing between the two the anticoagulant is the better of the two providing the best protection from clots and some protection from blockage.

About you question of a balance between risk and reward.... All you need do is see and talk to someone who has had a stroke, seeing the lifestyle going forward with speech problems, balance problems, paralyzation of the face and other parts, memory loss, etc... and realizing that this will continue for the rest of your life and the choice becomes easier. A stroke really scares me and I would choose the anticoagulant every time!

Ian, speaking on the permanent AF and not being sufficient to treat, AF not only causes stroke risk to increase but also causes enlargement of the atria, thickening of the atria walls and weakening of the heart muscle so I don't believe that there is an AF that is not sufficient to treat. It can lead to many different heart conditions down the road.

Mark, Yes there are new procedures coming out that are proving to be quite successful in "stopping AF". Also about the choice to remain on drug therapy becomes less of an option depending on your current age. Most studies show that one can expect to effectively control AF with meds for up to 15 or so years. Since AF increases in frequency and strength over time, meds normally will not work effectively forever. For a person like me in the late 50's or 60's you might be successful but for someone in their 40's or younger that option usually does not work for long.

Mitch, As we go forward, you will see the Chads tables changing. They have already changed some and are working on the others. Also remember that the Chads table are developed for general stroke risk and not specific to AF so the recommendation for aspirin depends on the type of stroke risk you have. The problem lies in not realizing that aspirin does not help prevent clots in AF the option for aspirin or anticoagulant for a score of 1 should be changed.

Bob, I agree.... Re-training the older Drs is a major task and most will just rely on what they learned 20 years ago.

Anyway... Thank you all for the comments!



Thanks Tim a full, thoughtful and knowledgeable answer as always I really value your posts.

You say A Fib not only can cause stroke (agreed fully) but can cause atrial enlargement and thickening of the walls and weakening of the muscle.

I specifically asked my cardio if leaving my A Fib untreated would damage my heart and he said no, I already have a slightly enlarged atria, which he says could either be the cause OR a result of the A Fib.

From my reading, the damage is caused when someone has an "attack" or their heartbeat races over 100 and the sort of paroxsymal A Fib which so many have got. I understand that sometimes the atria can race at up to 3 times the speed of the ventricles and this is the damaging part

My heartbeat only goes over 90 when I exercise, despite the permanent A Fib, (I think I have permanent now not persistent as they are not treaing) my heart seldom races, and my blood pressure and even cholesterol is "normal" at nearly all times.

So you will understand, that having been sent off for six month before I see my cardio again, I am keen to understand this fully.

Many sites I have researched say I could carry this until 95 without any further sign of problems and others say it only ever gets worse.

Right now I am resigned to warfarin for life, I am trying hard to make some lifestyle changes and see if that helps, but honestly I have no symptoms, sure I am acutely aware of my heartbeat, but it's simply regularly irregular all the time.

If however every month that passes that I am untreated makes to future worse, then I need to re-evaluate




"Yes I have a high calcium score, although the CT scan showed no significant blockages, and it may well be for that reason that the aspirin is given." That's exactly my situation, and echoes what my GP said.

Excellent posting! Many thanks



hi great information thanks so much , i am now 63, very much on the go , im a very young 63 always doing something even though i get very tired.

i have sarcoidosis, in many areas of my body as well as a,fib sarcoid since 1974 , a ,fib since last year, im irish and i just dont understand my tretment at all. i am on the tablet i was told is new called xarelto 20 mg per day , arythmol150 twice a day and bisop 5mg twice a day. i the a and e doctor told me my tablets are not working but the specialist read my notes and said to leave my appointment stand as it is and not marked urgent as it was when i went to and e , my family doctor said he has to catch my a fib in action before he writes me a letter , but he is appointment only. i sometimes am frightened when the heartbeat gets very low 34 bpm, but i never faint, so he said not to worry , im so uses to going from 140 down to 34 up down 70 90 50 0n and up , so out of sinus rhythem even when im sitting down in the evening . i dont smoke drink or drink coffee. do my tablets seem to be the usual or is there a usual, i dont know anyone inperson who has a fib in dublin, i appreciate that it can only be an openion that you can give me , so thank you in advance


Hi Nannygoat,

The Xarelto is one of the new blood thinners to prevent you having strokes. The other tablets are to try to prevent the irregular heart beat (arythmol) and reduce the heart rate (bisoprolol). It doesn't sound as though the last 2 are working. There are alternatives so it's worth asking your specialist what else is available, when you eventually see him.

As regards the family doctor, do they have an ECG machine? If so, the next time you get AF, ring the nurse and get an ECG there and then. The nurse can do that. That's all the evidence you need. Alternatively and perhaps best of all get a 7 day Holter ( a machine that records your heart rhythm for 7 days) but that might be more difficult to organise.

I'm sure there are 10's of thousands of others in Dublin that have AF, although they may not be aware of it or suffer in silence.



thank you Mark.


what about aspirin with nattokinase. Was told by a natural doctor that nattokinase and aspirin could be used in place of anticoagulant.


Really I think everyone should !ook up the dangers of the new anticoagulants on the web particularly Rivaroxoban....there are lawsuits going on in the USA because of this dangerous drug. More info on nattokinase please which I take in the hope that it is preventing blood clots forming.


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