atrial fibrillation (AF)

Last edited 05/2024

Atrial fibrillation is a supraventricular tachyarrhythmia characterised by ineffective, chaotic, irregular and rapid (300 to 600 beats per minute) atrial activity resulting in the deterioration of atrial mechanical function (1).

AF is the most common sustained cardiac arrhythmia seen in the general population (2)

• in majority, it is thought to be caused by rapidly firing cells located at the junction of the pulmonary veins with the left atrial musculature (3)
• these rapidly firing impulses are responsible for disorganized atrial depolarization and ineffective atrial contractions
• in turn, it results in an irregular ventricular rate because the impulses from the atria approach the atrioventricular node from varying angles and at varying intervals.

Atrial fibrillation is often seen in the elderly and generally is asymptomatic. If atrial fibrillation occurs when there is a large atrium, for example in mitral stenosis, then this is a predisposing factor to the development of thromboembolism.

Structural, functional, and electrophysiological changes resulting from a complex interplay of risk factors are thought to be responsible for the initiation, progression, and maintenance of atrial fibrillation (5):

• in many patients, these changes may include:
  • left ventricular hypertrophy
  • diastolic dysfunction
  • left atrial enlargement
  • left atrial fibrosis
  • left atrial stiffness
  • autonomic dysfunction
• in some patients with atrial fibrillation especially in young patients, no identifiable risk factors may exist, suggesting a possible genetic predisposition
• atrial fibrillation can by itself sustain and further promote atrial, ventricular, and systemic structural and functional alterations

Stroke risk

• use the CHA2DS2-VASc stroke risk score to assess stroke risk in people with any of the following (4):
  • symptomatic or asymptomatic paroxysmal, persistent or permanent atrial fibrillation
  • atrial flutter
  • a continuing risk of arrhythmia recurrence after cardioversion back to sinus rhythm

Bleeding risk

• assess the risk of bleeding when:
  • considering starting anticoagulation in people with atrial fibrillation and
  • reviewing people already taking anticoagulation
• use the ORBIT bleeding risk score to assess bleeding risk (4)
• offer monitoring and support to modify risk factors for bleeding, including (4):
  • uncontrolled hypertension
  • poor control of international normalised ratio (INR) in patients on vitamin K antagonists
  • Concurrent medication, including antiplatelets, selective serotonin reuptake inhibitors (SSRIs) and non-steroidal anti-inflammatory drugs (NSAIDs)
  • harmful alcohol consumption
  • reversible causes of anaemia

Anticoagulation in chronic atrial fibrillation (4)

• anticoagulation may be with apixaban, dabigatran etexilate, rivaroxaban or a vitamin K antagonist
  • consider anticoagulation for men a CHA2DS2-VASc score of 1. Take the bleeding risk into account
    • apixaban, dabigatran, edoxaban and rivaroxaban are all recommended as options (4)
  • offer anticoagulation to people with a CHA2DS2-VASc score of 2 or above, taking bleeding risk into account
    • apixaban, dabigatran, edoxaban and rivaroxaban are all recommended as options (4)
  • if direct-acting oral anticoagulants are contraindicated, not tolerated or not suitable in people with atrial fibrillation, offer a vitamin K antagonist (4)
  • do not offer stroke prevention therapy to people aged under 65 years with atrial fibrillation and no risk factors other than their sex (that is, very low risk of stroke equating to a CHA2DS2-VASc score of 0 for men or 1 for women)
  • do not withhold anticoagulation solely because of a person's age or their risk of falls (4)

Excess mortality (5):

• atrial fibrillation is associated with a nearly twofold excess risk of all-cause mortality

Antiplatelets

• do not offer aspirin monotherapy solely for stroke prevention to people with atrial fibrillation (4)

Classification of AF (5):

• atrial fibrillation is classified as "paroxysmal" if episodes terminate spontaneously or after targeted intervention within seven days, whereas atrial fibrillation lasting more than seven days without termination is considered "persistent" and often requires electrical or pharmacological cardioversion for termination
• atrial fibrillation that persists continuously for longer than a year is termed "longstanding persistent atrial fibrillation"
• when the patient and clinician decide not to pursue any attempt to restore normal rhythm, atrial fibrillation is considered "permanent"

A proportion of patients with embolic stroke of undetermined source (ESUS) have silent atrial fibrillation (AF) or develop AF after the initial evaluation (6):

• besides age as the most important variable, several other factors, including hypertension, higher body mass index, and lack of diabetes, are independent predictors of AF after ESUS
• when baseline NT-proBNP was available, only older age and elevation of this biomarker were predictive of subsequent AF

Lifetime risk of heart failure if a person has AF:

• a Danish cohort study showed that, in individuals with atrial fibrillation, about two in five developed heart failure (7)

Notes:

• for adults with atrial fibrillation who are already taking a vitamin K antagonist and are stable, continue with their current medication and discuss the option of switching treatment at their next routine appointment, taking into account the person's time in therapeutic range (4)

Reference:

1. American Heart Association (2011). ACCF/AHA Pocket Guideline. Management of patients with atrial fibrillation.
2. European Heart Rhythm Association et al.Guidelines for the management of atrial fibrillation: the Task Force for the Management of Atrial Fibrillation of the European Society of Cardiology (ESC). Eur Heart J. 2010 (19):2369-429.
3. British Heart Foundation (2004). FF85 Factfile: Atrial Fibrillation - an update
4. NICE (April 2021). Atrial fibrillation: the management of atrial fibrillation
5. Ponamgi SP et al. Screening and management of atrial fibrillation in primary care. BMJ 2021;372:mn379 http://dx.doi.org/10.1136/bmj.mn379
6. Bahit MC, Sacco RL, Easton JD, Meyerhoff J, Cronin L, Kleine E, Grauer C, Brueckmann M, Diener HC, Lopes RD, Brainin M, Lyrer P, Wachter R, Segura T, Granger CB. Predictors of Development of Atrial Fibrillation in Patients With Embolic Stroke Of Undetermined Source: An Analysis of the RE-SPECT ESUS Trial. Circulation. 2021 Oct 15. doi: 10.1161/CIRCULATIONAHA.121.055176. Epub ahead of print. PMID: 34649459
7. Vinter N, Cordsen P, Johnsen S P, Staerk L, Benjamin E J, Frost L et al. Temporal trends in lifetime risks of atrial fibrillation and its complications between 2000 and 2022: Danish, nationwide, population based cohort study BMJ 2024; 385:e077209 doi:10.1136/bmj-2023-077209