Atrial Fibrillation and Stroke Prevention

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What is Atrial Fibrillation?

Atrial fibrillation (AF), sometimes referred to as atrial fib, is a condition which affects 3 to 5 percent of people over the age of 65. It is an abnormal heart rate and rhythm that is caused by the irregular and rapid beating of the upper chambers of the heart (atria), resulting in ineffective pumping of blood to the lower chambers (ventricles).

When blood is incompletely pumped out sludging and formation of blood clots may occur. These blood clots may pass through the small arteries of the body, and when this occurs in the brain the result is a stroke. About 15% of strokes are caused by atrial fib, and these are usually disabling if not fatal.

Although the likelihood of developing AF increases with age, strokes are highly preventable.

Treatment for Atrial Fib

Since stroke is a major complication of atrial fib, aggressive treatment of AF is recommended to prevent stroke. These measures include:

  • Drugs to decrease heart rate associated with AF like beta-blockers, digoxin, amiodarone and quinidine
  • Electrical cardioversion, which is an electrical shock applied to the heart if unresponsive to drugs
  • Radiofrequency ablation, which destroys tissue causing abnormalities in the heart rhythm
  • Implantation of atrial pacemakers to regulate heart rhythm
  • Surgery to disrupt tissues causing faulty electrical pathways

Atrial Fibrillation and Stroke Prevention

Aside from treating AF directly, another strategy for preventing stroke is to prevent the entry of blood clots to the circulation and into the brain.

The process by which blood clots originating from the heart are thrown off to the circulation and getting lodged into the small caliber arteries feeding the vital organs is called thromboembolism. In the case of atrial fib slow delivery of blood from the atria to the ventricles cause adhesion of platelets to each other and to the walls of the heart, forming clots or thrombi which travel as emboli.

In addition, blood clotting is also a result of a mechanism triggered by proteins in the blood plasma resulting in coagulation. These complex mechanisms normally prevent hemorrhage or uncontrolled bleeding from happening when the body encounters an injury. However these processes are exaggerated when there are abnormalities in the circulation.

Therefore, to prevent stroke, doctors often prescribe blood thinners in the form of:

  • Anticoagulants – prevent normal mechanisms of coagulation to take place, thus avoiding formation of blood clots; examples are warfarin and heparin
  • Antiplatelet medications – the most popular is aspirin, which decrease platelet activation and clot formation

Warfarin is known to be very effective and is considered superior to aspirin in preventing the formation of blood clots. However, like other anticoagulants it can cause internal bleeding which can be fatal and uncontrolled bleeding when injured. Therefore its use demands strict monitoring. Furthermore, it has many drug and dietary interactions which complicate its chronic use.

Aspirin is recommended for patients older than 75 years of age and at lower risk for stroke. It may also cause gastrointestinal ulcers, bleeding, bronchospasm and ringing in the ear. However, these are easily reversed by stopping its intake.

  • Different studies have investigated the effects of combining an antiplatelet with an anticoagulant drug. Evidence of the combination’s effectiveness in decreasing the risk of stroke is lacking and the risk of complications is great.
  • Other studies also investigated the benefits of combining aspirin with another antiplatelet drug like clopidogrel. Findings show that the risk of stroke is reduced but complications may be increased.
  • Another type of drug that can prevent stroke is a direct thrombin inhibitor, like Dabigatran etexilate and Ximelagatran. Still undergoing clinical investigation, these drugs still have to show evidence on their beneficial effects.
  • Still another potential drug that can prevent stroke is Idraparinux, which has similar chemical properties as heparin. However it also bears a higher risk of bleeding compared to warfarin.

Treatment of atrial fibrillation and stroke prevention can result in a decreased risk of mortality. The careful use of drugs in preventing stroke is accomplished by strict medical supervision with the cooperation of the patient and the help of caregivers in the case of older patients.

References

NCBI, “Update on Antithrombotic Therapy for Stroke Prevention in Atrial Fibrillation” accessed on 1/27/11

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2860552/

AHA, “Atrial Fibrillation” accessed on 1/27/11

https://www.americanheart.org/presenter.jhtml?identifier=4451