Atrial fibrillation overview
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Atrial fibrillation (AF or afib) is a cardiac arrhythmia (abnormal heart rhythm) that involves the two upper chambers (atria) of the heart. Atrial fibrillation is an irregularly irregular heart beat due to chaotic firing of the impulses in the atrium. In this rhythm, the atrium is stimulated chaotically by a wide number of ectopic foci of electrical activity.
Although several clinical classification plans and protocols have been proposed, none of them fully account for all aspects of atrial fibrillation. The American Heart Association, American College of Cardiology, and the European Society of Cardiology have proposed the a classification system based on simplicity and clinical relevance. It contains four main categories of atrial fibrillation; first detected, paroxysmal, persistent, and permanent.
In atrial fibrillation, the normal electrical impulses that are generated by the sinoatrial node are overwhelmed by disorganized electrical impulses that originate in the atria and pulmonary veins, leading to conduction of irregular impulses to the ventricles that generate the heartbeat. The result is an irregular heartbeat which may occur in episodes lasting from minutes to weeks, or atrial fibrillation may be present continuously for years.
The most common cause of atrial fibrillation is atrial dilation associated with hypertension. Approximately 1/3 of patients have familial atrial fibrillation which is due to an underlying genetic disorder. Given the number of patients who undergo coronary artery bypass grafting in the developed world, this is an increasing underlying cause of atrial fibrillation. Other general causes include the advancing age of the population this hemodynamic stress of heart failure and valvular heart disease, myocardial ischemia, a variety of inflammatory disorders, pulmonary diseases, alcohol and drug abuse, and endocrine disorders.
Differentiating Atrial Fibrillation from other Diseases
Atrial fibrillation must be distinguished from other common atrial arrhythmias, which include atrial flutter, atrial tachycardia, paroxysmal supraventricular tachycardia, Wolff-Parkinson-White syndrome, and atrioventricular nodal reentry tachycardia.
Epidemiology and Demographics
AF is the most common arrhythmia. The risk of atrial fibrillation increases with age, and 8% of people over the age of 80 have AF. It accounts for 1/3 of hospital admissions for cardiac rhythm disturbances, and the rate of admissions for AF has risen in recent years.
Screening for atrial fibrillation is generally not performed, although a study of routine pulse checks or electrocardiograms during routine office visits found that the annual rate of detection of atrial fibrillation in elderly patients improved from 1.04% to 1.63%.
Natural History, Complications and Prognosis
Atrial fibrillation can be complicated by embolic events including stroke and systemic embolization. The atrial kick (active filling of the left ventricle by atrial contraction) often contributes importantly to the filling of the left ventricle, and the loss of the atrial kick can be associated with the development of congestive heart failure.
History and Symptoms
Atrial fibrillation is often be identified by taking the pulse and observing that the heartbeats don't occur at regular intervals. The pulse is classically irregularly irregular.
The absence of P waves on the electrocardiogram with an irregularly irregular atrial rhythm is diagnostic of atrial fibrillation.
Chest X Ray
A chest-x-ray is useful in the setting of atrial fibrillation only when the cause is suspected to be pulmonary in origin.
Performing an echocardiogram in the setting of atrial fibrillation is essential to identify certain characteristics of the heart, including valvular heart disease, hypertrophy, presence of thrombus, the size and function of the left ventricle, the size of the atria, and the possible presence of pericardial disease.
Cardiac magnetic resonance imaging may be used to assess the structure and the function of the atria in patients with atrial fibrillation. Further studies are needed to determine whether CMR is useful for detecting atrial thrombi in persons with atrial fibrillation.
Other Imaging Studies
Other diagnostic studies include the holter monitor to assess symptomatic episodes of atrial fibrillation over a 24 hour period, and exercise stress testing to assess a how a patient's heart rate responds to exertion. The main benefits to performing an exercise stress test are to reproduce exercise induced atrial fibrillation, and to exclude ischemia before initiating treatment with type 1C antiarrhythmic medications.
Atrial fibrillation may be treated with medications which either slow the heart rate or revert the heart rhythm back to normal sinus rhythm. Synchronized electrical cardioversion may also be used to convert AF to a normal heart rhythm. Surgical and catheter-based therapies may also be used to prevent recurrence of AF in certain individuals. People with AF are often given anticoagulants such as warfarin to reduce the risk of stroke.
Among patients in whom there is normal atrioventricular conduction, fibrillatory or irregular impulses that vary in timing, amplitude and shape are present which are in turn associated with the rapid irregular ventricular response that characterizes atrial fibrillation. 
Oral anticoagulation is a mainstay of atrial fibrillation management. For both primary and secondary prevention of stroke, there is a 61% relative risks reduction in the incidence of all cause stroke (both ischemic and hemorrhagic) associated with adjusted-dose oral anticoagulation.
Atrial fibrillation with rapid ventricular rate is a common finding in many hospitalized patients. The ventricular rate may be increased upto 150-170. It is essential to bring the ventricular rate down to less than 100 because a rapid ventricular response can cause hemodynamic instabilities and tachycardia mediated cardiomyopathies (heart failure). 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. This can significantly increase mortality and morbidity, which can be prevented by early and adequate treatment of the AF.
Prophylactic antiarrhythmic drug therapy may be required to maintain sinus rhythm, reduce frequency of symptoms, improve hemodynamic function and exercise capacity and prevent tachycardia-induced cardiomyopathy secondary to atrial fibrillation. In patients with heart failure, pharmacological maintenance of sinus rhythm has shown to reduce morbidity.
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.
A surgical option for some patients with atrial fibrillation is the maze procedure. In this procedure, a series of incisions in a cross like pattern are made on the atria, which blocks the abnormal atrial circuits, hence eliminating the atrial fibrillation. A number of improvements have been made to this surgical procedure since it was first invented.
In patients with paroxysmal atrial fibrillation, or after conversion of persistent AF, dronedarone is a medication that may be used to decrease the need for hospitalization, and can be started as an outpatient therapy. It can not be given in patients with class IV heart failure, decompensated heart failure, or depressed left ventricular function. A permanent pacemaker is not recommended in patients who do not have another indication for placement of a pacemaker.
- ↑ 1.0 1.1 1.2 Fuster V, Rydén LE, Cannom DS, et al (2006). "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): developed in collaboration with the European Heart Rhythm Association and the Heart Rhythm Society". Circulation 114 (7): e257-354. doi:10.1161/CIRCULATIONAHA.106.177292. PMID 16908781.
- ↑ Friberg J, Buch P, Scharling H, Gadsbphioll N, Jensen GB. (2003). "Rising rates of hospital admissions for atrial fibrillation". Epidemiology 14 (6): 666–72. doi:10.1097/01.ede.0000091649.26364.c0. PMID 14569181.
- ↑ Fitzmaurice DA, Hobbs FD, Jowett S, et al (2007). "Screening versus routine practice in detection of atrial fibrillation in patients aged 65 or over: cluster randomized controlled trial". doi:10.1136/bmj.39280.660567.55. PMID 17673732.
- ↑ Bellet S. Clinical Disorders of the Heart Beat. 3rd ed. Philadelphia: Lea& Febiger, 1971
- ↑ Shea, Julie B.; William H. Maisel (2002). "Cardioversion". Circulation 106 (22): e176–8. doi:10.1161/01.CIR.0000040586.24302.B9. PMID 12451016.
- ↑ Hart RG, Benavente O, McBride R, Pearce LA (October 1999). "Antithrombotic therapy to prevent stroke in patients with atrial fibrillation: a meta-analysis". Ann. Intern. Med. 131 (7): 492–501.
- ↑ Torp-Pedersen C, Møller M, Bloch-Thomsen PE, Køber L, Sandøe E, Egstrup K et al. (1999) Dofetilide in patients with congestive heart failure and left ventricular dysfunction. Danish Investigations of Arrhythmia and Mortality on Dofetilide Study Group. N Engl J Med 341 (12):857-65. DOI:10.1056/NEJM199909163411201 PMID: 10486417
- ↑ Deedwania PC, Singh BN, Ellenbogen K, Fisher S, Fletcher R, Singh SN (1998) Spontaneous conversion and maintenance of sinus rhythm by amiodarone in patients with heart failure and atrial fibrillation: observations from the veterans affairs congestive heart failure survival trial of antiarrhythmic therapy (CHF-STAT). The Department of Veterans Affairs CHF-STAT Investigators. Circulation 98 (23):2574-9. PMID: 9843465
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