Lesson topic №26. Фибрилляция предсердий (Atrial Fibrillation)

Atrial fibrillation

Other irregular rhythms

may resemble atrial fibrillation on ECG but can be distinguished by the presence of discrete P or flutter waves, which can sometimes be made more visible with vagal maneuvers.

Muscle tremor or electrical interference may resemble f waves, but the underlying rhythm is regular.

Atrial fibrillation may also cause a phenomenon that mimics ventricular extrasystoles or ventricular tachycardia (Ashman phenomenon).

This phenomenon typically occurs when a short R-R interval follows a long R-R interval; the longer interval lengthens the refractory period of the infra-Hisian conduction system, and the subsequent QRS complex(es) are conducted aberrantly, typically with right bundle branch morphology.

Echocardiography and thyroid function tests

are important in the initial evaluation.

Echocardiography is done to assess structural heart defects (eg, left atrial enlargement, left ventricular wall motion abnormalities suggesting past or present ischemia, valvular disorders, cardiomyopathy) and to identify additional risk factors for stroke (eg, atrial blood stasis or thrombus, complex aortic plaque).

Atrial thrombi are more likely in the atrial appendages, where they are best detected by transesophageal rather than transthoracic echocardiography.

•Atrial fibrillation with a wide QRS complex may indicate Wolff-Parkinson-White syndrome;

•in such cases, use of AV node-blocking medications may be fatal.

Treatment of Atrial Fibrillation

•Rate control with medications or AV node ablation

•Sometimes rhythm control with synchronized cardioversion, medications, or atrial fibrillation substrate ablation

•Prevention of thromboembolism

If a significant underlying disorder is suspected, patients with new-onset atrial fibrillation may benefit from hospitalization.

Patients with recurrent episodes do not require hospitalization unless other symptoms suggest the need for it.

Once causes have been managed, treatment of atrial fibrillation focuses on ventricular rate control, rhythm control, and prevention of thromboembolism.

Ventricular rate control

Patients with atrial fibrillation of any duration require rate control (typically to < 100 beats/minute at rest) to control symptoms and prevent tachycardia-induced cardiomyopathy.

For acute paroxysms of rapid rate (eg, 140 to 160 beats/minute), IV AV node blockers are used (for doses, see table Antiarrhythmic Drugs).

CAUTION: AV node blockers should not be used in patients with Wolff-Parkinson-White syndrome when an accessory AV pathway is involved (indicated by wide QRS duration); these drugs increase frequency of conduction via the bypass tract, possibly causing ventricular fibrillation.

Beta-blockers (eg, metoprolol, esmolol) are preferred if excess catecholamines are suspected (eg, in thyroid disorders, exercise-triggered cases).

Nondihydropyridine calcium channel blockers (eg, verapamil, diltiazem) are also effective.

Digoxin is the least effective but may be preferred if heart failure is present.

These medications may be used orally for long-term rate control.

When beta-blockers, nondihydropyridine calcium channel blockers, and digoxin—separately or in combination—are ineffective, amiodarone may be required.

Rhythm control

In patients with heart failure or other hemodynamic compromise directly attributable to new-onset atrial fibrillation, restoration of normal sinus rhythm is indicated to improve cardiac output.

In other cases, conversion of atrial fibrillation to normal sinus rhythm is optimal, but the antiarrhythmic medications that are capable of doing so (class Ia, Ic, III) have a risk of adverse effects and may increase mortality.

Conversion to sinus rhythm does not eliminate the need for chronic anticoagulation. For acute conversion, synchronized cardioversion or drugs can be used.

Before conversion is attempted, the ventricular rate should be controlled to < 120 beats/minute, and, many patients should be anticoagulated (for criteria and methods, see Prevention of thromboembolism during rhythm control).

If atrial fibrillation has been present > 48 hours, patients should typically be given an oral anticoagulant (conversion, regardless of method used, increases risk of thromboembolism).

Anticoagulation should be maintained for > 3 weeks before conversion or can be given for a shorter time before conversion if transesophageal echocardiography (TEE) does not show left atrial thrombus.

Anticoagulation should be continued for at least 4 weeks after cardioversion.

Many patients need chronic anticoagulation (see Long-term measures to prevent thromboembolism).

Synchronized cardioversion

(100 joules, followed by 200 and 360 joules as needed) converts atrial fibrillation to normal sinus rhythm in 75 to 90% of patients, although recurrence rate is high.

Efficacy and maintenance of sinus rhythm after the procedure is improved with use of class Ia, Ic, or III antiarrhythmic medications 24 to 48 hours before the procedure.

Cardioversion is more effective in patients with shorter duration of atrial fibrillation, lone atrial fibrillation, or atrial fibrillation with a reversible cause;

it is less effective when the left atrium is enlarged (> 5 cm), atrial appendage flow is low, or a significant underlying structural heart disorder is present

Pearls & Pitfalls

•When possible, give anticoagulation before attempting to convert atrial fibrillation to sinus rhythm.

•Conversion to sinus rhythm does not eliminate the need for chronic anticoagulation in patients who meet criteria for it.

Medications for conversion of atrial fibrillation to sinus rhythm

include class Ia (procainamide, quinidine, disopyramide), Ic (flecainide, propafenone), and III (amiodarone, dofetilide, dronedarone, ibutilide, sotalol, vernakalant) antiarrhythmics (see table Antiarrhythmic drugs).

All are effective in about 50 to 60% of patients, but adverse effects differ.

These medications should not be used until rate has been controlled by a beta-blocker or nondihydropyridine calcium channel blocker.

The converting medications with oral formulations are also used for long-term maintenance of sinus rhythm (with or without previous cardioversion).

Choice depends on patient tolerance. However, for paroxysmal AF that occurs only or almost only at rest or during sleep when vagal tone is high, medications with vagolytic effects (eg, disopyramide) may be particularly effective.

Exercise-induced AF may be better prevented with a beta-blocker.