- Clinical science
Atrial fibrillation (AF, Afib) is a common supraventricular tachyarrhythmia that is caused by uncoordinated atrial activation resulting in an irregular ventricular response. The exact mechanisms that lead to AF are poorly understood, but a number of cardiac and noncardiac risk factors are associated with AF. Patients are often asymptomatic but have an irregularly irregular pulse on physical examination. When present, symptoms usually include palpitations, lightheadedness, shortness of breath or features of embolic stroke. The relative stagnation of blood in the atria due to ineffective atrial emptying promotes clot formation, which in turn increases the risk of stroke and other thromboembolic complications. The diagnosis is confirmed by an ECG that shows indiscernible P waves and a narrow but irregular QRS complex. A Holter monitor or event recorder is used to diagnose intermittent episodes. Echocardiography is useful in ruling out structural heart disease, and to detect the presence of atrial thrombi. AF with symptoms of hemodynamic instability should always be treated with immediate synchronized cardioversion. Treatment of AF among hemodynamically stable patients consists of anticoagulation therapy to prevent thromboembolic complications and the use of rate or rhythm control strategies to prevent the symptoms of AF and atrial remodeling. The need for anticoagulation therapy is determined based on the CHA2DS2-VASc score. Therapy should be individualized in high-risk patients after considering the risks (particularly life-threatening bleeding) versus benefits (reduced risk of stroke) of anticoagulation. Rate control therapy typically involves the use of beta-blockers or nondihydropyridine calcium channel blockers. Rhythm control strategies involve elective synchronized cardioversion and/or the use of antiarrhythmics such as flecainide, propafenone, ibutilide, dofetilide, or amiodarone. Rate control therapy is usually preferred but the preferred treatment strategy may vary depending on the treatment center and the presence or absence of other comorbidities. Catheter directed or surgical ablation of the arrhythmogenic tissue is a newer modality used in refractory or severe AF.
Atrial flutter is another common supraventricular tachyarrhythmia that is usually caused by a single macroreentrant rhythm within the atria. The risk factors for atrial flutter are similar to those of AF. However, the atrial rate is slower, the QRS rhythm is usually regular, and characteristic saw-toothed P waves are seen on an ECG. Treatment is similar to that of AF, consisting of anticoagulation, and rate or rhythm control strategies. Atrial flutter frequently degenerates into atrial fibrillation.
- Most common sustained arrhythmia
- Peak incidence: risk of AF increases with age
- Sex: ♂ > ♀ (7:5)
- Race: slightly higher prevalence among whites
- Prevalence: 2.7–6.1 million people in the USA (∼ 1% of the entire population)
Epidemiological data refers to the US, unless otherwise specified.
While direct causes of atrial fibrillation are not known, many risk factors for AF exist .
|Risk factors for atrial fibrillation|
|Cardiovascular risk factors||Intrinsic cardiac disorders||Noncardiac disorders|
In approx. 15% of cases, AF occurs in the absence of any of the above risk factors (idiopathic / lone AF).
|Hemodynamic stability||Unstable AF||AF patients who present with chest pain, altered mental status, acute pulmonary edema, hypotension and/or other signs of shock|
|Stable AF||AF patients who are hemodynamically stable|
|Heart rate||AF with rapid ventricular response||AF with a ventricular rate > 100 bpm (tachycardic AF)|
|Slow AF||AF with a ventricular rate < 60 bpm (bradycardic AF)|
|Onset and duration of AF||New-onset AF||AF less than 48 hours in duration|
|Paroxysmal AF||AF that terminates within 7 days of onset either following treatment or spontaneously|
|Persistent AF||Continuous AF for > 7 days|
|Long-standing persistent AF||Continuous AF for > 1 year|
|Permanent AF||Long-standing persistent AF that is not treated following a joint decision by the patient and the physician|
|Mitral valve involvement||Valvular atrial fibrillation||AF in patients with mitral valve stenosis, artificial heart valves, and/or repaired mitral valves|
|Non-valvular atrial fibrillation||AF in patients without mitral valve involvement → moderately elevated risk of thromboembolic events|
Mitral valve involvement should always be assessed in patients with AF!
- Atrial fibrillation is a .
Three steps, which perpetuate a vicious cycle are responsible for the pathogenesis of AF:
- AF is initiated by one or both of the following mechanisms:
AF is sustained by re-entry rhythms and/or rapid focal ectopic firing
- Re-entry rhythms are more likely to occur with enlarged atria, diseased heart tissue, and/or aberrant pathways (e.g., Wolff-Parkinson-White syndrome).
- Unlike atrial flutter, the re-entry circuits in the case of AF are microreentry rhythms (< 4 mm) and therefore cannot be mapped by cardiac catheterization.
- Atrial remodeling
- Effects of AF
- Most patients are asymptomatic
- Less commonly, symptoms of such as palpitations, dizziness, syncope, fatigue, and or dyspnea
- Symptoms of the underlying disease (e.g., murmurs of mitral stenosis)
- Tachycardia with an irregularly irregular pulse
- Apex-pulse deficit
- Absent a-waves in the JVP
- Variable intensity of S1
- Complications of long-standing AF
Patients with atrial fibrillation may be asymptomatic for long periods of time!
ECG (initial investigation)
- Irregularly irregular RR intervals
- P-waves are indiscernible; instead, many fine or coarse atrial fibrillatory waves (f waves) with a frequency of 350–600 bpm may be seen (markedly in lead V1)
- Narrow QRS complex (< 0.12 seconds)
Transthoracic echocardiogram (TTE)
- Indications: all patients with new-onset AF
- Assesses cardiac function and rule out underlying structural cardiac disease, e.g., mitral valve stenosis
Transesophageal echocardiogram (TEE)
- Indications: patients with AF or atrial flutter > 48 hours or of unknown duration for whom electrical or pharmacological cardioversion is planned, but who have not received anticoagulation therapy for at least 3 preceding weeks
- Visualizes the atria and the left atrial appendage (hotspots for thrombogenesis) to identify thrombi before attempting cardioversion
- Further assesses heart function and rules out underlying structural disease
- Transthoracic echocardiogram (TTE)
Laboratory tests: to identify underlying risk factors for AF
- Troponin levels: to rule out myocardial infarction
- D-dimer levels: if risk factors (e.g., DVT) or clinical features of pulmonary embolism are present
- Brain-natriuretic peptide (BNP): to identify heart failure
- CBC: to identify anemia, infection
- TSH, fT4: to screen for hyperthyroidism
- Serum electrolytes (Na+, K+, Mg2+, and Ca2+): to identify electrolyte imbalances
- BUN, serum creatinine: to identify chronic kidney disease
- Ethanol levels, digoxin levels and/or urine toxicology (e.g., cocaine, amphetamines)
The general principles of treating atrial fibrillation include:
- Correcting reversible causes and/or treatable conditions (e.g., hyperthyroidism, electrolyte imbalances)
- Controlling heart rate and/or rhythm
- Providing anticoagulation
Controlling heart rate and/or rhythm
- Unstable AF: emergent
- Stable AF: rate control or rhythm control strategies to control AF and prevent long-term recurrence (see table below)
|Treatment strategy||Rate control||Rhythm control|
|Goal and rationale|| || |
|Indications|| || |
|Contraindications|| || |
|Therapeutic measures||1st line|
|2nd line (ablative procedures)|| |
Patients with unstable AF should be treated with immediate cardioversion!
Prerequisites for cardioversion of AF
New onset AF (< 48 hours) in patients with:
- Low thromboembolic risk (see below) → consider anticoagulation directly before or after cardioversion
- High thromboembolic risk → start anticoagulation immediately before or after cardioversion
- Anticoagulation options: IV heparin or LMWH, direct thrombin inhibitors (e.g., dabigatran), or factor Xa inhibitors (e.g., rivaroxaban, apixaban)
AF ≥ 48 hours or of unknown duration in patients with:
Unstable AF (require urgent cardioversion): IV heparin or LMWH immediately before cardioversion followed by warfarin for up to 4 weeks after cardioversion
- TEE to rule out atrial thrombi recommended if anticoagulation has not been administered at least 3 week prior to cardioversion
- Stable AF (do not require urgent cardioversion): warfarin with bridging therapy for 3 weeks before and up to 4 weeks after cardioversion
- Unstable AF (require urgent cardioversion): IV heparin or LMWH immediately before cardioversion followed by warfarin for up to 4 weeks after cardioversion
Anticoagulation therapy should be considered in all patients who are about to undergo cardioversion.
|CHA2DS2-VASc score||Indications for long-term anticoagulation|
|C||CHF or left-sided heart failure||1|| |
|A2||Age ≥ 75||2|
|S2||Stroke or TIA or thromboembolism||2|
|V||Vascular disease (prior MI, peripheral artery disease, or aortic plaque)||1|
|Sc||Sex category (female sex)||1|
|CHA2DS2-VASc scores of 1, 2, 3, 5, and ≥6 carry an annual stroke risk of approx. 1%, 2%, 3%, 7%, and >9% respectively.|
Long term anticoagulation for patients with AF in order to prevent thromboembolic complications is indicated if the patient has an underlying valvular disease, hypertrophic cardiomyopathy, and/or a CHA2DS2-VASc score ≥ 2
The risk of bleeding due to anticoagulation should always be taken into consideration when initiating anticoagulation therapy
- Atrial flutter is a that is usually caused by a single macroreentrant rhythm within the atria.
- Incidence: 88 per 100,000 person-years
- Sex: ♂ > ♀ (5:2)
- Peak incidence: risk of atrial flutter increases with age
- Etiology: similar to atrial fibrillation (see “Etiology” above) In addition to the risk factors mentioned above, cardiac surgery and/or ablative procedures that are used to treat AF are additional risk factors, which are usually associated with atypical atrial flutter.
Type I (common, typical, or isthmus-dependent flutter)
- Caused by a counterclockwise (more common) or clockwise (less common) macroreentrant rhythm in the right atria that passes through cavotricuspid isthmus
- Atrial rate of 250–350 bpm and 2:1 atrioventricular conduction
Type II; (rare, atypical atrial flutter):
- Various reentrant rhythms that do not involve the cardio-tricuspid isthmus, are not well defined, and/or occur in the left atrium
- Atrial rate of 250–450 bpm and 2:1 atrioventricular conduction
- Type I (common, typical, or isthmus-dependent flutter)
- Clinical features
- Diagnostics (similar to atrial fibrillation; see “Diagnostics” above)
- Treatment: similar to atrial fibrillation (see “Therapy” above)
- Frequently degenerates into atrial fibrillation (see “Clinical features” above)
- 1:1 conduction leading to life-threatening ventricular tachycardia