Atrial fibrillation

BASIC INFORMATION
DEFINITION
Atrial fibrillation is one of the most common arrhythmias, affecting 7% of the population at age 60 or older (Fig. 14.1). In contrast to atrial flutter, the ventricular rate during atrial fibrillation is absolutely irregular due to the chaotic fibrillatory activity in the atria at very high rates (>300 beats/min). However, the arrhythmia may become somewhat regular at rapid ventricular rates. Every absolutely irregular rhythm is considered atrial fibrillation until proven otherwise, even in the absence of identifiable P waves and even with wide QRS complexes. Conversely, a very regular tachycardia rules out the diagnosis of atrial fibrillation (DD: atrial flutter, junctional rhythm). Atrial fibrillation is classified as being paroxysmal (self-terminating), persistent (sustained atrial fibrillation that can only be returned to sinus rhythm by cardioversion), or permanent (sustained atrial fibrillation that is either resistant to, or not appropriate for cardioversion). The causes of paroxysmal atrial fibrillation are listed in Tab. 14. Commonly, atrial fibrillation, atrial flutter, and atrial tachycardias occur in the same patient and can induce one another.

Fig. 14.1 Atrial fibrillation. Note the absolutely irregular rhythm and the lack of P waves.

Table 14 Causes of atrial fibrillation

Symptoms and signs

Symptoms attributable to atrial fibrillation are highly variable. In some patients (about 30%) it is an incidental finding, whilst others attend hospital as an emergency following the onset of atrial fibrillation. Most patients experience some deterioration of exercise capacity or well-being, but this may only be appreciated once sinus rhythm is restored. When caused by rheumatic mitral stenosis, the onset of atrial fibrillation results in considerable worsening of cardiac failure.
     The patient has a very irregular pulse, as opposed to a basically regular pulse with an occasional irregularity (e.g. extrasystoles) or recurring irregular patterns (e.g. Wenckebach block). The irregular nature of the pulse in atrial fibrillation is maintained during exercise.
     The ECG shows fine oscillations of the baseline (so-called fibrillation or f waves) and no clear P waves. The QRS rhythm is rapid and irregular. Untreated, the ventricular rate is usually 120-180 per minute, but it slows with treatment.
     The clinical classification of atrial fibrillation includes first detected, paroxysmal, persistent, and permanent forms of the arrhythmia and is essential for the decision-making between rhythm restoration and rate control. For example, atrial fibrillation may be asymptomatic and the ‘first detected episode’ should not be regarded as necessarily the true onset.
SYNONYMS
AF
A-fib
EPIDEMIOLOGY & DEMOGRAPHICS
The prevalence of atrial fibrillation increases with age, from 2% in the general population to 5% in patients older than 60 yr.
PHYSICAL FINDINGS & CLINICAL PRESENTATION
Clinical presentation is variable:
• Most common complaint: palpitations
• Fatigue, dizziness, light-headedness in some patients
• A few completely asymptomatic patients
• Cardiac auscultation revealing irregularly irregular rhythm
ETIOLOGY
• Coronary artery disease
• MS, MR, AS, AR
• Thyrotoxicosis
• Pulmonary embolism, COPD
• Pericarditis

• Myocarditis, cardiomyopathy
• Tachycardia-bradycardia syndrome
• Alcohol abuse
• MI
• WPW syndrome
• Other causes: left atrial myxoma, atrial septal defect, carbon monoxide poisoning, pheochromocytoma, idiopathic
DIAGNOSIS
DIFFERENTIAL DIAGNOSIS
• Multifocal atrial tachycardia
• Atrial flutter
• Frequent atrial premature beats
WORKUP
New-onset atrial fibrillation: ECG, echocardiogram, Holter monitor, and laboratory evaluation
LABORATORY TESTS
• TSH, free T4
• Electrolytes
IMAGING STUDIES
• ECG
1. Irregular, nonperiodic wave forms (best seen in V1) reflecting continuous atrial reentry
2. Absence of P waves
3. Conducted QRS complexes showing no periodicity
• Echocardiography to evaluate left atrial size and detect valvular disorders
• Holter monitor: useful only in selected patients to evaluate paroxysmal atrial fibrillation

TREATMENT
NONPHARMACOLOGIC THERAPY
• Avoidance of alcohol in patients with suspected excessive alcohol use
• Avoidance of caffeine and nicotine
ACUTE GENERAL Rx
• If the patient is hemodynamically stable, treatment options include IV diltiazem, verapamil, digoxin, or propranolol.
• IV heparin or SC low-molecular-weight heparin
• Cardioversion is indicated if the ventricular rate is >140 bpm and the patient is symptomatic (particularly in acute MI, chest pain, dyspnea, CHF) or when there is no conversion to normal sinus rhythm after 3 days of pharmacologic therapy. The likelihood of cardioversion-related clinical thromboembolism is low in patients with atrial fibrillation lasting < 48 hr. Patients with atrial fibrillation lasting > 2 days have a 5% to 7% risk of clinical thromboembolism if cardioversion is not preceded by several weeks of warfarin therapy. However, if transesophageal echocardiography reveals no atrial thrombus, cardioversion may be performed safely after only a short period of anticoagulant therapy. Anticoagulant therapy should be continued for at least 1 mo after cardioversion to minimize the incidence of adverse thromboembolic events following conversion from atrial fibrillation to sinus rhythm.
• Anticoagulate with warfarin (unless patient has specific contraindications).
• Long-term anticoagulation with warfarin (adjusted to maintain an INR of 2 to 3) is indicated in all patients with atrial fibrillation and associated cardiovascular disease, including the following:
1. Rheumatic valvular disease (MS, MR, AI)
2. Aortic stenosis
3. Prostatic mitral valve
4. History of previous embolism
5. Known cardiac thrombus
6. CHF
7. Cardiomyopathy with poor left ventricular function
8. Nonrheumatic heart disease (e.g., hypertensive cardiovascular disease, coronary artery disease, ASD)
9. Anticoagulation is generally not recommended in young patients with lone atrial fibrillation.
• Medical cardioversion:
1. Attempts at medical (pharmacologic) intervention should be considered only after proper anticoagulation because cardioversion can lead to systemic emboli. Following successful cardioversion, anticoagulation with warfarin should be continued for 4 wk.
2. Useful agents for medical cardioversion are quinidine, flecainide, propafenone, amiodarone, ibutilide, sotalol, dofetilide, and procainamide
3. Amiodarone appears to be the most effective agent for converting to sinus rhythm in patients who do not respond to other agents.
4. Procainamide is the preferred agent for pharmacologic cardioversion in the presence of WPW syndrome.
CHRONIC Rx
• Anticoagulation with warfarin (see “Acute General Rx”)
• Rate control with digoxin
DISPOSITION
Factors associated with maintenance of sinus rhythm following cardioversion:
• Left atrium diameter <60 mm
• Absence of mitral valve disease
• Short duration of atrial fibrillation
REFERRAL
Surgical treatment of atrial fibrillation:
• The maze procedure with its recent modifications creating electrical barriers to the macroreentrant circuits that are thought to underlie atrial fibrillation is being performed with good results in several medical centers (preservation of sinus rhythm in >95% of patients without the use of long-term antiarrhythmic medication). Clear indications for its use remain undefined. Generally surgery is reserved for patients with rapid heart rate refractory to pharmacologic therapy or who cannot tolerate pharmacologic therapy.
• Catheter-based radiofrequency ablation procedures designed to eliminate atrial fibrillation are being performed; studies on long-term survival of these patients are pending.
• Implantable atrial defibrillators combine the option of atrial defibrillation with the capacity for ventricular defibrillation. Clinical experience for these devices remains limited. Their main indication is patients with highly symptomatic paroxysmal atrial fibrillation resistant to other therapies or patients with paroxysmal atrial fibrillation and coexisting ventricular arrhythmias.