Atrial fibrillation

Atrial fibrillation (AF or AFib) is a cardiac arrhythmia (an abnormality of heart rate or rhythm) originating in the atria. Abnormal electrical impulses in the atria cause the ventricles to contract erratically. AF is the most common cardiac arrhythmia. If rapid, it may compromise blood flow and cause fainting, orthostatic hypotension (low blood pressure on standing up) or low blood pressure. In addition, it predisposes to thrombosis and embolism to the brain, being a prime risk factor for stroke.

Treatment

Rate and rhythm control

AF can cause disabling and annoying symptoms. Palpitations, angina, lassitude, and decreased exercise tolerance are related to rapid heart rate and inefficient cardiac output caused by AF. There are two ways to approach these symptoms: rate control and rhythm control. Rate control treatments seek to reduce the heart rate to normal, usually 60 to 100 beats per minute. Rhythm control seeks to restore the normal heart rhythm, called normal sinus rhythm. Studies suggest that rhythm control is mainly a concern in newly diagnosed AF, while rate control is more important in the chronic phase. Rate control with anticoagulation is as effective a treatment as rhythm control in long term mortality studies, the AFFIRM Trial{{fn|2}}.

Related Topics:
Palpitations - Angina

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AF can cause a form of heart failure called tachycardia-induced cardiomyopathy. This can significantly increase mortality and morbidity. The early treatment of AF through either rate-control or rhythm-control can prevent this condition and thereby improve mortality and morbidity.

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Rate control

Rate control methods include:

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• beta blockers (e.g. )
• digoxin
• calcium channel blockers (e.g. verapamil)

In refractory cases where none of the above drugs are sufficient, amiodarone or clonidine may be used, accepting the small risk of their toxicities.

Related Topics:
Amiodarone - Clonidine

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These medications work by slowing the generation of impulses from the atria and the conduction of those impulse from the atria to the ventricles.

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In patients with AF where rate control drugs are ineffective and it is not possible to restore sinus rhythm using cardioversion, non-pharmacological alternatives are available. For example, to control rate it is possible to destroy the bundle of cells connecting the upper and lower chambers of the heart - the atrioventricular node - which regulates heart rate, and to implant a pacemaker instead. A more complex technique involves ablating groups of cells near the pulmonary arteries where atrial fibrillation is thought to originate.

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Rhythm control

Rhythm control methods include electrical and chemical cardioversion:

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• electrical cardioversion involves the restoration of normal heart rhythm either through the application of a DC electrical shock (electrical cardioverion)
• chemical cardioversion is performed with drugs, such as amiodarone, propafenone or flecainide.

The anti-arrhythmic medications often used in either pharmacological cardioversion or in the prevention of relapse to AF alter the flux of ions in heart tissue, making them less excitable, setting the stage for spontaneous and durable cardioversion. These medications are often used in concert with electrical cardioversion. However, the AFFIRM study showed no difference in risk of stroke in patients who have converted to a normal rhythm with anti-arrhythmic treatment, compared to those who have only rate control.{{fn|2}}.

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Whichever method of cardioversion is used, approximately 50% of patient relapse within one year, although the continued daily use of oral antiarrhythmic drugs may extend this period. The key risk factor for relapse is duration of AF, although other risk factors that have been identified include the presence of structural heart disease, and increasing age.

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RFA

Radiofrequency ablation (RFA) uses radiofrequency energy to destroy abnormal electrical pathways in heart tissue. It is used in recurrent AF. The energy emitting probe (electrode) is placed into the heart through a catheter. The practitioner first "maps" an area of the heart to locate the abnormal electrical activity before the responsible tissue is eliminated. Ablation is a newer technique and has shown some promise for cases unresponsive to conventional treatments. New techniques include the use of cryoablation (tissue freezing using a coolant which flows through the catheter), and microwave ablation, where tissue is ablated by the microwave energy "cooking" the adjacent tissue. The abnormal electrophysiology can also be modified in a similar way surgically, and this procedure - referred to as the Cox maze procedure - is commonly performed concomitantly with cardiac surgery.

Related Topics:
Radiofrequency ablation - Electrode - Catheter

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This is an area of active research, especially with respect to the RF ablation technique and emphasis on isolating the pulmonary veins that enter into the left atrium.

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Anticoagulation

In confirmed AF, anticoagulant treatment is a crucial way to prevent stroke. Treatment of AF patients over age 60 with warfarin (also known as Coumadin®) results in a significant reduction in the subsequent risk of stroke. Patients under age 65 who have any structural heart disease (ie: valvular heart disease, ejection fraction

Related Topics:
Anticoagulant - Stroke - Warfarin - Ejection fraction - Heart attack - Aspirin - New - Ximelagatran

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