Atrial Fibrillation

See also the related article which covers Atrial Flutter.
The most common type of cardiac arrhythmia, characterised by irregularly irregular ventricular pulse and loss of association between the cardiac apex beat and radial pulsation. Atrial fibrillation may be paroxysmal (self-limiting), persistent (amenable to cardioversion) or permanent¹. Loss of active ventricular filling is associated with:

• Stagnation of blood in the atria leading to thrombus formation and a risk of embolism, increasing the risk of stroke
• Reduction in cardiac output (especially during exercise) which may lead to heart failure.

• Prevalence is approximately 1% of the population¹
• Prevalence increases with age and is above 5% in people aged over 65 years². It is uncommon in those under 50 years
• More common in males than females.

• Idiopathic ('lone') atrial fibrillation: 5-10% of patients. It is a diagnosis of exclusion with no evidence of any specific underlying cause
• Hypertension: especially with associated left ventricular hypertrophy
• Coronary heart disease
• Valvular heart disease, especially mitral valve stenosis
• Atrial septal defect
• Atrial myxoma
• Sick sinus syndrome
• Pre-excitation syndromes with accessory conduction pathways, e.g. Wolff-Parkinson-White syndrome
• Dilated and hypertrophic cardiomyopathy
• Pericardial disease, e.g. pericardial effusion, constrictive pericarditis
• Hyperthyroidism
• Acute infections, especially pneumonia in the elderly
• Acute excess alcohol intake or chronic excess alcohol intake
• Respiratory: lung cancer, pleural effusion, pulmonary embolism
• Other causes include haemochromatosis, sarcoidosis, and narcotic abuse
• Genetic: autosomal dominant (rare).

Clinical presentation is very variable between being asymptomatic and causing severe heart failure:

• Asymptomatic in up to 20% of patients: detected as an irregularly irregular pulse rhythm with the cardiac apex rate exceeding the wrist pulse rate, or found incidentally on an ECG
• Palpitations: paroxysmal or persistent
• Heart failure, lethargy, fatigue, dyspnoea, chest pain, dizziness
• Syncope is rare unless patient has sick sinus syndrome or Wolff-Parkinson-White syndrome
• Arterial pulse is irregularly irregular in rhythm, rate and volume
• First heart sound of variable loudness
• Absent 'a' waves in jugular venous pulse
• Apical-radial pulse mismatch develops when the rate is rapid.

• Atrial flutter
• Atrial extrasystoles
• Supraventricular tachyarrhythmias
• Atrioventricular nodal re-entrant tachycardia
• Wolff-Parkinson-White syndrome
• Ventricular tachycardia.

Further assessment is focused on identifying any underlying cause and assessment of cardiac function:

• ECG:
  • Diagnostic except in paroxysmal atrial fibrillation between attacks
  • Distinguishing feature of atrial fibrillation is variability in the R-R intervals
  • Ambulatory ECG monitoring and event recorders may be required
• Thyroid function tests, full blood count (anaemia may precipitate heart failure), renal function and electrolytes (abnormal serum potassium levels can potentiate arrhythmias, especially if the patient is taking, or about to start, digoxin), liver function tests and coagulation screen (pre-warfarin)
• Chest x-ray:
  • May indicate cardiac structural causes of atrial fibrillation such as mitral valve disease
  • May indicate heart failure
• Echocardiogram:
  • Evaluate underlying cardiac function, structural abnormalities, evidence of coronary artery disease or pericardial fluid
  • If immediate cardioversion is considered, it is also used to detect any thrombus formation
• CT scan of the brain:
  • Useful if neurological examination is suggestive of a secondary stroke
• Associated Diseases Wolff-Parkinson-White syndrome: in these patients, atrial fibrillation can lead to rapid ventricular rates and ventricular fibrillation, especially when AV nodal blocking agents are used.

• Lifestyle changes: particularly where the arrhythmia is associated with alcohol or caffeine ingestion
• Treat any underlying cause, e.g. acute infection, hyperthyroidism. Atrial fibrillation may revert on treatment or resolution of an associated problem, e.g. acute infection or alcohol intoxication. No further intervention may be required, other than avoiding the precipitating factor (e.g. alcohol, caffeine)
• Treat associated heart failure
• Rate or rhythm control: several studies tend to support rate control over rhythm control, including the PIAF study³
• Recent studies^4,5 have shown that restoring and maintaining sinus rhythm neither improves the survival rate or reduces the risk of stroke. Therefore rate control is advocated for most patients with atrial fibrillation.
• The NICE guidelines recommend trying rhythm control first for patients with persistent AF who are symptomatic, younger, presenting for the first time with lone AF, secondary to a corrected underlying cause or if congestive heart failure. The guidelines recommend trying rate control first for patients who are over 65, with coronary artery disease, with contraindications to antiarrhythmic drugs and those unsuitable for cardioversion⁶.

Rate control

• The target ventricular rate (measured on an ECG or at the ventricular apex, but not the wrist) is below 80 per minute at rest and 90-115 on moderate exercise
• A heart rate-limiting calcium-channel blocker (e.g verapamil or diltiazem) or a beta-blocker are recommended as first-line therapy for control of the ventricular rate⁶. Verapamil should not be combined with a beta-blocker because of the risk of heart block and asystole. Sotalol should not be used just for rate control because it is associated with an increased incidence of ventricular arrhythmias¹
• Digoxin may control the resting heart rate, but rarely adequately controls heart rate during exertion and so should only be considered as monotherapy in predominantly sedentary patients⁶. Digoxin is still considered as initial therapy in patients with heart failure due to left ventricular systolic dysfunction, but these patients should still receive a beta-blocker later
• Often a combination of two drugs may be needed and, in this case, digoxin can be combined with either a rate-limiting calcium-channel blocker or a beta-blocker
• Pacemaker: In patients with paroxysmal atrial fibrillation and/or flutter in whom medical therapy has failed, atrial overdrive pacing has been shown to decrease recurrent episodes of atrial fibrillation and atrial flutter.
• Radio-frequency ablation of the AV node and pacemaker implantation has also been used for resistant cases, but does not remove the need for anticoagulation or improve mortality.
• Ventricular rate control is more difficult for atrial flutter but can be achieved with drugs that block the AV node. Calcium channel blockers (eg, verapamil, diltiazem) or beta-blockers can be effective. The ventricular rate at rest can sometimes be controlled with digoxin.

Rhythm control with restoration and maintenance of sinus rhythm

Cardioversion

• If the duration is more than 48 hours and thrombus cannot be excluded by echocardiogram, anticoagulation therapy is required for four weeks prior to elective cardioversion
• If the duration is less than 48 hours duration, the risk of embolic stroke is small and pre-cardioversion anticoagulation is not required
• Conversion to sinus rhythm may cause embolisation in the period up to 2-3 weeks after cardioversion, so anticoagulation is required until 4-6 weeks after sinus rhythm is restored, whether or not thrombus was initially present
• Indications for cardioversion:
  • Recent onset atrial fibrillation: but not always clear when it started
  • No structural heart disease
  • Successful treatment of precipitating cause, e.g. thyrotoxicosis, chest infection
  • Young age - but elderly are not excluded
  • Acute AF and severe hypotension, acute heart failure, acute myocardial infarction or unstable angina - need urgent cardioversion
  • DC cardioversion is safe (thromboembolism in less than 1%) and effective in both atrial fibrillation (80-80% success rate) and atrial flutter (success rate over 95%).

For pharmacological cardioversion

• Oral amiodarone is effective in converting atrial fibrillation to normal sinus rhythm and is also the most effective in preventing relapse after cardioversion, but has significant side effects and can enhance the anticoagulant effect of warfarin
• Flecainide and propafenone are also recommended but should not be used in patients with structural heart disease, coronary heart disease, left ventricular dysfunction or severe left ventricular hypertrophy¹
• Patients with structural heart disease are more susceptible to severe complications from pharmacological cardioversion⁷
• Recommended drugs for maintaining sinus rhythm are amiodarone, disopyramide, flecainide and propafenone.

Prevention of stroke

• Warfarin substantially reduces risk of stroke by about 70%. The INR should be kept between 2-3 to optimize the therapeutic effect and minimize the risk of bleeding. A lower INR target of 1.5-3.0 has been shown to be safe and effective in the over 75 year age group
• Aspirin is less effective than oral anticoagulation in atrial fibrillation and, unless contraindicated, all elderly patients should receive warfarin. Aspirin is advocated for patients aged under 65 years and with no clinical or echocardiographic risk factors
• Early results from The Stroke Prevention Using Oral Thrombin Inhibitor in Atrial Fibrillation (SPORTIF) III and V trials⁸ have suggested that ximelagatran may be an effective and safe alternative to warfarin in the future
• Adequate anticoagulation has been shown to decrease thromboembolic complications in patients with persistent or paroxysmal atrial flutter and in patients who are undergoing cardioversion. Patients with atrial flutter are anticoagulated in the same way as for atrial fibrillation.
  The NICE guidelines for stroke prevention in patients with paroxysmal, persistent or permanent AF are⁶:
  • High risk: anticoagulation with warfarin. High risk is defined as:
    • Previous stroke/TIA/thromboembolic event
    • Age 75 years or over with hypertension, diabetes or vascular disease
    • Clinical evidence of valve disease or heart failure, or impaired LV function on echocardiography
  • Low risk: aspirin 75-300mg if no contraindications. Low risk is defined as:
    • Age under 65 years with no moderate or high risk factors
  • Medium risk: consider anticoagulation or aspirin. Medium risk is defined as:
    • Age 65 years or older with no high risk factors
    • Age under 75 with hypertension, diabetes or vascular disease

Referral

The NICE guidelines recommend further specialist intervention (e.g. for pulmonary vein isolation, pacemaker insertion, surgery, AV junction ablation or use of atrial defibrillators for⁶:

• When pharmacological therapy has failed
• With lone AF
• With ECG evidence of any underlying electrophysiological disorder, e.g. Wolff-Parkinson-White syndrome

Other interventions

• In resistant cases, radiofrequency ablation of aberrant conduction pathways or radio-ablation of the AV node and permanent pacemaker may be considered
• Other procedures include cryoablation, microwave ablation and high-intensity focused ultrasound
• The Maze procedure is an option for patients with atrial fibrillation who are also undergoing mitral valve procedures. Its role as a primary therapy for atrial fibrillation is doubtful.

• Atrial fibrillation increases risk of stroke six-fold (much more in patients with rheumatic heart disease), and becomes increasingly important as a risk factor for stroke with increasing age. Paroxysmal as well as persistent atrial fibrillation increases risk of stroke
• The risk of stroke is less in patients with no other structural heart disease ('lone AF')
• Atrial fibrillation can also precipitate acute heart failure and aggravate established heart failure
• Chronic atrial tachyarrhythmia may lead to cardiomyopathy
• Atrial fibrillation is associated with an approximate doubling of the risk of premature death.

• Atrial fibrillation is associated with reduced life expectancy in older patients
• Prognosis depends on the patient's underlying medical condition. Any atrial arrhythmia can cause a tachycardia-induced cardiomyopathy
• Atrial fibrillation is associated with a doubling of morbidity and mortality from cardiovascular disease and is the commonest cause of embolic stroke.

• Smoking cessation: smoking is a risk factor for coronary heart disease as well as a precipitating factor for atrial fibrillation
• Alcohol moderation or avoidance: acute alcoholic intoxication or alcohol withdrawal may precipitate paroxysmal atrial fibrillation
• Diet: caffeine may induce paroxysmal atrial fibrillation in susceptible individuals.