Anticoagulation and Stroke Prevention

Scan of brain

The most dreaded complication of atrial fibrillation is stroke. In atrial fibrillation, the atria of the heart do not beat effectively, which allows the blood to "pool" within these chambers.

As a result, an atrial thrombus (blood clot) can form. Eventually, the atrial thrombus can embolize—that is, it can break loose and travel through the arteries. All too often, this embolus will lodge in the brain, and the result is a stroke.

So if you have atrial fibrillation, your doctor should do a formal estimate of your risk of stroke, and if that risk is high enough, you should be placed on treatment to prevent blood clots from forming, and thus, to prevent a stroke.

Estimating Your Risk

Estimating your risk of stroke if you have atrial fibrillation requires taking into account your age, sex, and certain medical conditions you might have. First, if you have significant valvular heart disease in addition to atrial fibrillation, you will need therapy to prevent blood clots, since your risk of stroke is substantially elevated.

If you don't have heart valve disease, your doctor will probably use a risk calculator, called the CHA2DS2-VASc score, to estimate your risk of stroke. In people with atrial fibrillation, the higher the CHA2DS2-VASc score, the higher the risk of stroke. The CHA2DS2-VASc score ranges from zero to nine points and is calculated as follows:

  • Congestive heart failure = one point
  • Hypertension = one point
  • Age 75 or higher = two points
  • Diabetes = one point
  • Prior stroke or TIA = two points
  • Peripheral artery disease = one point
  • Age between 64 to 74 = one point
  • Female sex = one point

The higher the CHA2DS2-VASc score, the higher the annual risk of stroke.

So, if your score is zero, your risk of stroke is 0.2 percent per year, which is quite low. If your score is two, the annual risk is 2.2 percent, and it rises rapidly from there. A score of nine yields an annual risk of stroke of 12.2 percent. (By way of comparison, for every 100 people over the age of 65 with no atrial fibrillation, about one per year will have a stroke.)

Reducing Stroke Risk

The use of anticoagulant drugs can greatly reduce the risk that an embolus from the left atrium will cause a stroke in people with atrial fibrillation. However, these drugs themselves carry a risk of producing a major bleeding episode, including hemorrhagic stroke (bleeding in the brain). It is estimated that the average annual risk of stroke caused by anticoagulants is 0.4 percent.

What this means is that using anticoagulant drugs makes sense when the risk of stroke from atrial fibrillation is substantially greater than the risk of stroke from the drug. Doctors agree, for the most part, that in patients with nonvalvular atrial fibrillation whose CHA2DS2-VASc score is zero, anticoagulation should not be used.

For scores of two or higher, anticoagulant drugs should almost always be used. And for scores of one, treatment needs to be individualized for each patient.

In the past, doctors assumed that if they were successful in applying "rhythm control therapy" for atrial fibrillation (that is, treatment aimed at stopping atrial fibrillation and maintaining a normal heart rhythm), the risk of stroke would drop. However, clinical evidence so far has failed to show that rhythm control therapy reduces the risk of stroke. So even if you and your doctor opt for rhythm control therapy, you should still be treated to prevent stroke if your CHA2DS2-VASc score is high enough.

Which Drugs to Use?

The drugs that are effective in reducing the risk of stroke in atrial fibrillation are the anticoagulant drugs. These are drugs that inhibit the blood's clotting factors, and thus inhibit the formation of blood clots. In patients with atrial fibrillation, anticoagulation reduces the risk of stroke quite substantially—by about two-thirds.

Until just a few years ago, the only chronic oral anticoagulant drug that was available was warfarin (Coumadin), a drug that inhibits vitamin K. (Vitamin K is responsible for making many of the clotting factors.) Taking Coumadin is notoriously inconvenient and often difficult, however. Periodic and often frequent blood testing is needed to measure the “thinness” of the blood and adjust the dose of Coumadin. Also, dietary restrictions are needed since many foods can alter the action of Coumadin. If the dosage is not adjusted properly or often enough, the blood can become “too thin” or not thin enough, and either one can cause serious problems.

In the last few years, several new anticoagulation drugs have been developed that do not act by inhibiting vitamin K, but instead by directly inhibiting certain clotting factors. These are called the “novel anticoagulant” drugs, or NOACs. NOACs currently approved in the U.S. are dabigatran (Pradaxa), rivaroxaban (Xarelto), apixaban (Eliquis), and edoxaban (Savaysa).

These drugs all have advantages over Coumadin. They use fixed daily doses, so the need for frequent blood tests and dosage adjustments is eliminated. They do not require any dietary restrictions. And clinical studies have demonstrated these newer drugs to be at least as effective and as safe as Coumadin.

There are certain drawbacks to the NOACs, however. They are far more expensive than Coumadin, and unlike Coumadin (which can be quickly reversed by giving vitamin K) it is difficult to reverse their anticoagulant effect if a major bleeding problem should occur. (The exception so far is Pradaxa, an antidote to this drug was approved in October 2015.)

Most experts now prefer to use a NOAC drug over Coumadin in patients with atrial fibrillation. However, there are people in whom Coumadin is still the preferred option. Coumadin remains a good choice if you are taking Coumadin already and have been completely stabilized on the drug or if you would rather not take pills twice per day (which is required for Pradaxa and Eliquis) or if you cannot afford the presently high cost of the newer drugs.

Mechanical Methods

Because of the problems inherent in taking anticoagulant drugs, efforts have been ongoing to develop mechanical treatments to try to prevent stroke in patients with atrial fibrillation.  These methods have been aimed at isolating the left atrial appendage (a “pouch” of the left atrium that is left over from fetal development).  It turns out that most of the clots that form in the left atrium during atrial fibrillation are located in the atrial appendage.

The left atrial appendage can be isolated from the circulation using surgical methods or by inserting a special device into the appendage through a catheter. While they used clinically, both of these methods have major drawbacks, and at this point are reserved for special cases. 


Stroke is the most feared, and unfortunately the most common, major complication of atrial fibrillation. So lowering your risk of stroke is something you and your doctor must take very seriously. Fortunately, if you and your doctor approach the problem systematically—estimating your risk and treating accordingly—your odds of avoiding this issue will be greatly improved.


Fuster, V, Ryden, LE, Cannom, DS, et al. ACC/AHA/ESC 2006 Guidelines for the Management of Patients With Atrial Fibrillation A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients With Atrial Fibrillation). J Am Coll Cardiol 2006; 48:e149.

Fang MC, Go AS, Chang Y, et al. Comparison of risk stratification schemes to predict thromboembolism in people with nonvalvular atrial fibrillation. J Am Coll Cardiol 2008; 51:810.

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