Risk of stroke in patients with atrial fibrillation -with and without anticoagulation

Previously, I had commented on the risk of stroke in atrial fibrillation patients not treated with oral anticoagulants (OAC).In that commentary I quoted Dr. Overvad -"...current guidelines discrepancies also reflect the fact that the level of stroke risk among men with a score on 1 and women with a score of 2 is on the borderline of where the  impact of anticoagulation  treatment shifts from beneficial to harmful."  His comment seems reinforced by a recent publication in Circulation.

After that commentary I became aware of a very important -and perhaps dogma changing- article published in Circulation by GR Quinn. I added an addendum to that post but  the article is important enough to be highlighted in another commentary. I re-post that addendum here:

"Unfortunately I became aware of the 2016 Circulation article by GR Quinn et al after the above commentary was published.  That very important article  provides good reason to question the dogma that the CHA2DS2-VASc scores translate to fixed stoke rate. It is generally accepted that if a person's stroke rate is estimated to be 1-2% per year then treatment with an OAC offers a  net clinical benefit and that the risk score clearly relates to a quantitative stroke risk, e.g. a CHA2DS2-VASC score of 1 means the person has a risk of about 1 % per year and a score of 2 indicates a risk of 2%. 

However, analysis of 34 studies of patients not treated with anticoagulants demonstrated that the stroke rate varies widely in various cohorts. For example, with a risk score  of 2, 27% of the cohorts reported a stroke risk of less than 1% and 33% reported stroke risk greater than 2% per year. So the correlation between risk score and stroke risk varies with the cohort studied.The numbers from the Northern European studies formed the basis of the alleged relationship between the CHA2DS2-VASc score and annual stroke risk and the North American Cohort analyses indicate significantly lower ( about 1/3 of the European rate) stroke rates for untreated AF.

 Quoting from the authors conclusions: ' The majority of cohorts did not observe stroke rates that would indicate a clear expected net clinical benefit for anticoagulating AF patients with a CHA2DS2-VASc score of 1 or 2.' "


Prediction is difficult, especially the future. Neils Bohr 

The most that can be expected from any model is that it can supply a useful approximation
to reality .   George Box