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The main goals of treatment of atrial fibrillation are to prevent temporary circulatory instability and to prevent stroke. Rate and rhythm control are principally used to achieve the former, while anticoagulation may be required to decrease the risk of the latter. The primary factors determining atrial fibrillation treatment are duration and evidence of hemodynamic instability. Cardioversion is indicated with new onset AF (for less than 48 hours) and with hemodynamic instability. If rate and rhythm control can not be maintained by medication or cardioversion, ablation by a trained Electrophysiologist may be suggested.
AF can cause disabling and annoying symptoms. Palpitations, angina, lassitude (weariness), 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 (Wyse et al., 2002).
AF with a persistent rapid rate 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.
Rate control
Rate control methods include:
* Beta blockers (e.g. metoprolol)
* Cardiac glycosides (i.e. digoxin)
* Calcium channel blockers (i.e. diltiazem or verapamil)
These medications work by slowing the generation of impulses from the atria and the conduction of those impulse from the atria to the ventricles.
In refractory cases where none of the above drugs are sufficient, a variety of other antiarrhythmic drugs, most commonly including quinidine, flecainide, propafenone, disopyramide, sotalol, or amiodarone may be used. Of these, only propafenone, sotalol, and amiodarone (which possess some beta blocking activity) control the ventricular rate; the others may maintain sinus rhythm, but may actually increase the ventricular rate. Many of these drugs are less frequently used today than in the past. All (with the possible exception of amiodarone) increase the risk of ventricular tachycardia, which can be fatal. In symptomatic patients with normal heart function, however, the small increase in risk is usually felt to be acceptable. In the presence of heart failure, the only antiarrhythmic drugs thought to be safe are amiodarone and dofetilide. In the United States, it should be noted that many of these agents are not approved by the FDA for this use.
In emergencies, when circulatory collapse is imminent due to uncontrolled tachycardia, immediate cardioversion may be indicated.
Rhythm control
Rhythm control methods include electrical and chemical cardioversion:
* Electrical cardioversion involves the restoration of normal heart rhythm through the application of a DC electrical shock.
* Chemical cardioversion is performed with drugs, such as amiodarone, procainamide, ibutilide, 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.
The main risk of cardioversion is systemic embolization of a blood clot from the previously fibrillating left atrium. Cardioversion should not be performed without adequate anticoagulation in patients with more than 48 hours of atrial fibrillation. Cardioversion may be performed in instances of AF lasting more than 48 hours if a transesophogeal echocardiogram (TEE) demonstrates no evidence of clot within the heart.
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.
Radiofrequency ablation
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, which avoids the need for a pacemaker, involves ablating groups of cells near the pulmonary veins where atrial fibrillation is thought to originate, or creating more extensive lesions in an attempt to prevent atrial fibrillation from establishing itself.
Ablation is a newer technique and has shown some promise for cases of recurrent AF that are unresponsive to conventional treatments. Radiofrequency ablation (RFA) uses radiofrequency energy to destroy abnormal electrical pathways in heart tissue. The energy emitting probe (electrode) is placed into the heart through a catheter inserted into veins in the groin or neck. Electrodes that can detect electrical activity from inside the heart are also inserted, and the electrophysiologist uses these to "map" an area of the heart in order to locate the abnormal electrical activity before eliminating the responsible tissue.
Most AF ablations consist of isolating the pulmonary veins (PV), which are located on the posterior wall of the left atrium. All veins from the body (including neck and groin) lead to the right atrium. In order to get to the left atrium the catheters must get across the atrial septum. This is done by peircing a small hole in the septal wall. This is called a transeptal approach. Once in the left atrium, the physician may perform Wide Area Circumferencial Ablation (WACA) to electrically isolate the PVs from the left atrium.
Some more recent approaches to ablating AF is to target sites that are particularly disorganized in both atria as well as in the coronary sinus (CS). These sites are termed complex fractionated atrial electrogram (CFAE) sites[7]. It is believed by some that the CFAE sites are the cause of AF, or a combination of the PVs and CFAE sites are to blame. 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.
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. The main problem in 2006 is that the procedure is only 70-80% effective at best -- and causes stroke in about 1% of patients.
Cox maze Procedure
James Cox, MD, and associates developed the Cox maze procedure, an open-heart surgical procedure intended to eliminate atrial fibrillation, and performed the first one in 1987. "Maze" refers to the series of incisions made in the atria (upper chambers of the heart), which are arranged in a maze-like pattern. The intention was to eliminate AF by using incisional scars to block abnormal electrical circuits (atrial macroreentry) that AF requires. This procedure required an extensive series of endocardial (from the inside of the heart) incisions through both atria, a median sternotomy (vertical incision through the breastbone) and cardiopulmonary bypass (heart-lung machine). A series of improvements were made, culminating in 1992 in the Cox maze III procedure, which is now considered to be the "gold standard” for effective surgical cure of AF. The Cox maze III is sometimes referred to as the “traditional maze”, the “cut and sew maze”, or simply the "maze".
Minimaze surgical procedures
Minimaze surgery is minimally invasive cardiac surgery intended to cure atrial fibrillation. Minimaze refers to "mini" versions of the original maze procedure. These procedures are less invasive than the Cox maze procedure and do not require a median sternotomy (vertical incision in the breastbone) or cardiopulmonary bypass (heart-lung machine). These procedures use microwave, radiofrequency, or acoustic energy to ablate atrial tissue near the pulmonary veins.
Anticoagulation
In confirmed AF, anticoagulant treatment is a crucial way to prevent stroke. Treatment of AF patients over age 60, who also have one or more of: previous strokes (or warning strokes), hypertension (high blood pressure), diabetes, or congestive heart failure, with warfarin (also known as Coumadin® or Marevan®) results in a 60 to 70 percent reduction in the subsequent risk of stroke. Patients under age 65 who have any structural heart disease (i.e. valvular heart disease, ejection fraction <= 35%, history of heart attack) may also benefit from warfarin.
The use of warfarin is associated with a delayed clinical effect. It typically takes three to five days to achieve a demonstrable anticoagulant effect. Hence, if an immediate anticoagulant effect is required, physicians could use heparin or other heparinoids such as enoxaparin to provide early anticoagulation. In practice, urgent anticoagulation is seldom indicated. Even in the setting of stroke complicating atrial fibrillation, clinical trial results do not support the routine use of immediate anticoagulation.
Patients under age 65 who do not have structural heart disease (i.e. with LAF) do not require warfarin, and can be treated with aspirin or clopidogrel. There is evidence that aspirin and clopidogrel are effective when used together, but the combination is still inferior to warfarin. The new anticoagulant ximelagatran has been shown to prevent stroke with equal efficacy as warfarin, without the difficult monitoring process associated with warfarin and with possibly fewer adverse haemorrhagic events. Unfortunately, ximegalatran and other similar anticoagulant drugs (commonly referred to as direct thrombin inhibitors), have yet to be widely licensed. License applications for ximelegatran (made by AstraZeneca) have been rejected by both American and European licensing authorities, and its evaluation has been suspended in the UK. This is primarily due to concerns over possible liver toxicity.
Determining who should and should not receive anti-coagulation with warfarin is not easy. The CHADS2 score is the best validated method of determining risk of stroke (and therefore who should be anticoagulated). The UK NICE guidelines have instead opted for an algorithm approach. The underlying problem is that if a patient has a yearly risk of stroke that is less than 2%, then the risks associated with taking warfarin outweigh the risk of getting a stroke.
It is worth noting that patient with AF who are being rhythm controlled are not treated any differently from patients with permanent AF when it comes to determining anticoagulation.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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