It usually goes like this. Mrs Jones is a lady in her mid-70s with a history of controlled hypertension. An irregular pulse is detected by a practice nurse usually during a routine blood pressure check. Atrial fibrillation is confirmed on an ECG and she is referred to cardiology outpatients. We go through the history, examination and then onto the management. I usually break this down into management of symptoms and reduction of stroke risk. In the asymptomatic patient the former is usually very easy so we rapidly move onto the latter which is usually more challenging.
I explain that AF is associated with an increased risk of stroke. 10,000 people a year are admitted to hospital in the UK with a stroke and found to be in AF. Then we arrive at the moment of the consultation where the W word is mentioned. I have tried to introduce this gently using the word anticoagulation, talking about little clots in the heart, preventing them by thinning the blood but finally the W word has to come out: "So Mrs Jones I would recommend that we start you on Warfarin."
A moment later the patient looks crestfallen. The reply is usually a combination of 1) I don’t want to go onto warfarin; 2) I have a friend/relative/neighbour who is on it and they have had terrible trouble; 3) I was dreading you would say that; 4) Can’t I just continue with the aspirin after all that thins the blood too doesn’t it? 5) Can I leave it for now and take it if things get worse.
I usually ask the patient “What is your biggest worry?” and often the reply is: “I don’t want to have stroke!”
We are recommending more and more anticoagulation. The awareness of the increased stroke risk associated with AF is rising and there are comprehensive guidelines recommending anticoagulation which apply to ever increasing numbers of patients. Anticoagulation in AF is now regarded by the pharmaceutical industry as big business.
This made me consider the risks and benefits of different types of stroke prevention therapy for AF. Guidelines have made this easy. Calculate the CHADS2 or CHADSVASC score of the patient and if it is more than 1 for CHADS2 or 2 for CHADSVASC then anticoagulation is recommended. You don’t need to know or think about the absolute risk numbers just a simple addition. The guideline tells you when to start anticoagulation and of course if you follow the guidelines you can’t be criticised. On the other hand if the patient has a stroke and you didn't recommend warfarin then that is not good. If the patient has a serious bleed due to the warfarin then you can’t be criticised for following the guidelines, can you?
Sometimes it helpful to think about the actual numbers behind these guidelines to see exactly the benefits and risks of the different treatments. It is common to tell the patient that anticoagulation reduces risk of stroke by two thirds - impressive. Consider Mrs Jones, she has an annual estimated stroke risk of 4.3% and an annual bleeding risk of 0.6% according to the risk calculators. Treating her with aspirin reduces the risk of stroke to 3.4% (22% RRR; 0.9% ARR, with a 1 in 106 chance of benefit per year). The risk of major bleeding rises to 1.1% (1 in 222 chance of being harmed). So a miniscule chance of benefit and miniscule chance of harm. Giving warfarin reduces stroke risk to 1.4% (66% RRR; 2.9% ARR, with a 1 in 35 chance of benefit per year) but the risk of major bleeding rises to 3.1% (1 in
40 chance of being harmed).
If there are 1000 patients similar to this then by doing nothing 43 will have stroke and 6 of them a major bleed over the next year. Treat them all with warfarin prevents 29 strokes but cause 25 major bleeds. Treated them with aspirin prevents 9 strokes but cause 5 major bleeds. I guess it all depends on whether you fear stroke or bleeding more, major bleeding provided it is not cerebral haemorrhage is not usually associate with long term disability and so may be trying to compare apples with pears and remember the patients biggest fear was of having a stroke.
The current recommendation is that anyone with a CHADS2VASC score of 2 or more should be offered anticoagulation. It is clear that warfarin treatment is associated with a benefit. As doctors we tend to emphasise the positives and stress the 66% risk reduction with warfarin compared to the 22% with aspirin. We do not stress the 5-fold increase in the risk of major bleeding associated with warfarin.
There has been a huge interest in atrial fibrillation recently. Some of this has been driven by the availability of the new oral anticoagulant drugs and the intense advertising war between the different companies to position their drug as the most effective. This has also been accompanied by an awareness campaign to doctors regarding the stroke risk associated with atrial fibrillation as well as community clinics funded by the pharmaceutical industry intent on finding cases of atrial fibrillation and reviewing the anticoagulation treatment.
As physicians we tend to play down the harmful effects of the treatments and emphasise the positives. We want to practice according to the guidelines.
If you were the patient with AF and you were told you there was a 1:35 chance of benefit with warfarin and 1:40 chance of harm what would you do?
Dr Richard Bogle
The opinions expressed in this blog are strictly those of the author and should not be construed as the opinion or policy of my employers nor recommendations for your care or anyone else's. Always seek professional guidance instead.