introduction
Atrial fibrillation (AF) is the most common sustained heart rhythm abnormality in man.
An estimated 2.3 million American adults have been diagnosed with AF and the risk of developing this condition at any time after the age of 40 has been found to be 20-25% in individuals of European and East Asian descent.
Atrial fibrillation is caused by disruption of the normal functioning of the electrical system in the atria, the two upper chambers of the heart. Normally the electrical system stimulates the atria to contract regularly and in coordination with the ventricles, the lower chambers of heart. In AF the atria are stimulated to contract very irregularly and rapidly, up to 350 to 600 times per minute. This results in ineffective and uncoordinated contraction of the atria - the atria essentially quiver instead of contracting. Although a natural checkpoint between the upper and lower chambers protects the ventricles from overstimulation, the contraction rate of the ventricles (which is the same is the actual heart rate or pulse) is still irregular in AF and can be up to 220 beats per minute when not treated. Occasionally the pulse rate is very slow, necessitating pacemaker placement.
Symptoms of atrial fibrillation include heart palpitations, fatigue, dizziness, tightness in the chest and shortness of breath. Sometimes, patients with AF have no symptoms. Atrial fibrillation can also worsen symptoms due to other heart diseases such as heart failure and coronary artery disease. Some individuals with AF are always in atrial fibrillation (chronic or permanent AF) while others have episodes of AF.
Genetic variants are known to contribute to the risk of atrial fibrillation and up to a third of patients with AF have a family history of the disease. Recently a common genetic variant was identified near the PITX2 gene on chromosome 4 that increases the risk of AF.
The deCODEme Genetic Scan identifies the risk variant on chromosome 4 in individuals of European and East Asian descent and provides interpretation of the associated risk for development of atrial fibrillation. Sufficient information is currently not available regarding the association of this variant and AF in people of other ethnicities.
prevention
The feared complication of AF is stroke. The electrical disturbance and quivering of the atria promote blood clot formation in the upper chambers of the heart. If a clot forms, the danger is that the clot, or parts of it, can travel with the bloodstream to the brain or other organs (embolize). An embolic stroke will occur if the clot blocks one of the arteries supplying blood to the brain. Compared to other types of strokes, embolic strokes are generally more severe and more commonly recur. AF is associated with a significant four to five-fold increase in the risk of stroke and accounts for one third of all strokes in patients older than 65.
The goals of atrial fibrillation treatment include stroke prevention, restoration of normal heart rhythm and heart rate control. The treatment can be challenging and should be designed to meet the needs of each individual patient. The specific type of treatment depends on the contributing causes of atrial fibrillation, coexisting heart disease, if the disease is episodic or permanent and if the symptoms are interfering with daily activities and quality of life. Restoration of normal heart rhythm is often not possible. Anticoagulation (thinning of the blood) for stroke prevention is generally recommended for all patients older than 65 as well as younger patients who also have hypertension or other cardiovascular diseases.
more information
You can find out more information about AF by talking with your doctor and visiting these Web sites:The American Heart Association on Atrial Fibrillation
MedlinePlus Article on Atrial Fibrillation
National Heart, Lung, and Blood Institute on Atrial Fibrillation
Scientific Articles
Ellinor, P.T., Yi, B.A, & MacRae, C.A.(2008). Genetics of atrial fibrillation. Medical Clinics Of North America, 92(1), 41-51.Kannel, W.B.& Benjamin, E.J.(2008). Status of the epidemiology of atrial fibrillation. Medical Clinics Of North America,92(1), 17-40.
Lip, G.Y., Tse, H.F.(2007). Management of atrial fibrillation. Lancet, 370(9587), 604-618.
Markides, V.& Schilling, R.J.(2003). Atrial fibrillation: classification, pathophysiology, mechanisms and drug treatment. Heart, 89(8), 939-943.