Aetiology

Atrial fibrillation (AF) is associated with all types of cardiac disease, as well as many non-cardiac conditions.[1] 

The conditions most commonly associated with AF include:

  • Hypertension

  • Coronary artery disease

  • Heart failure

  • Valvular heart disease

  • Diabetes

  • Thyroid disease

  • Sleep-disordered breathing

  • COPD

Other conditions that are associated with AF include:

  • Atrial and ventricular dilation or hypertrophy

  • Electrophysiological abnormalities (e.g., sick sinus syndrome)

  • Congenital heart disease

  • Cardiac or juxtacardiac benign or malignant, primary, or metastatic tumours

  • Inflammatory or infiltrative disease (e.g., pericarditis, amyloidosis, myocarditis)

  • Age-induced atrial and ventricular fibrosis

  • Autonomic neuronal dysfunction

  • Alcohol and caffeine misuse

  • Non-cardiac pulmonary hypertension

  • Infections

  • Chronic kidney disease

In rare cases, AF may be familial or genetic, such as in Lamins A and C heart disease and other familial cardiomyopathy.[19]

Post-operative AF is common, particularly after cardiac surgery such as transplant, CABG, and valve replacement.[3] Although most episodes are self-terminating, there is an increased risk of recurrent AF in the years following the procedure.[3]

Lifestyle factors that increase the risk of AF include smoking, alcohol, obesity, and lack of physical activity.[1][2]​

Pathophysiology

Since its early description, several theories have evolved in our current understanding of pathophysiologies of AF.[20][21][22][23][24][25][26]​ Pathophysiology of AF involves multiple aetiologies and complex electrophysiological changes. AF is usually associated with anatomically and histologically abnormal atria as a result of underlying heart disease. Dilation of the atria with fibrosis and inflammation causes a difference in refractory periods within the atrial tissue and promotes electrical re-entry that results in AF. The fractionation of a mother wave into multiple wavelets in the presence of enlarged atria, in conjunction with the short refractory periods and slow conduction properties of the atria, lead to sustained AF. The presence of rapidly firing foci, typically in the pulmonary veins, may trigger AF, and this is sustained by fibrillatory conduction or multiple re-entrant circuits. Clinical cardiovascular disease entities, such as hypertension, congestive heart failure, and coronary disease, through mechanisms such as myocardial stretch and fibrosis with disruption in cell-to-cell coupling, can lead to triggers and cellular and electrical remodelling that may promote AF.[1][23]​​[27]​​

Classification

2023 ACC/AHA/ACCP/HRS guideline for the diagnosis and management of atrial fibrillation[1]

The 2023 American College of Cardiology/American Heart Association/American Association of Colleges of Pharmacy/Heart Rhythm Society (ACC/AHA/ACCP/HRS) guideline classifies AF using stages. This updated classification recognises AF as a progressive disease that requires different strategies for management at different stages, including prevention.

  • Stage 1: at risk for AF (presence of risk factors)

  • Stage 2: pre-AF (evidence of structural or electrical findings further predisposing patient to AF)

  • Stage 3: AF (patients may transition between substages)

    • Stage 3A: paroxysmal AF (intermittent, lasting up to 7 days)

    • Stage 3B: persistent AF (continuous and sustained for over 7 days and requires intervention)

    • Stage 3C: long-standing persistent AF (continuous AF lasting >12 months)

    • Stage 3D: successful AF ablation (free from AF after ablation or surgical intervention)

  • Stage 4: permanent AF (no further attempts at rhythm control)

2020 ESC guidelines for the diagnosis and management of atrial fibrillation developed in collaboration with the European Association for Cardio-Thoracic Surgery (EACTS)​[2]​

The European Society of Cardiology (ESC) classifies AF in terms of the presentation, duration, and frequency of episodes:

  • First diagnosed/new-onset AF: AF not diagnosed before, irrespective of its duration or the presence/severity of AF-related symptoms. May be symptomatic or asymptomatic (detected by physical examination or ECG).[3]

  • Paroxysmal AF: AF that terminates spontaneously or with intervention within 7 days

  • Persistent AF: AF that is continuously sustained beyond 7 days, including episodes terminated by cardioversion after 7 days or longer

  • Long-standing persistent AF: a sub-group of persistent AF that is continuous for >1 year in duration

  • Permanent AF: AF that is refractory to cardioversion and sinus rhythm cannot be restored or maintained, such that AF is accepted as a final rhythm. A decision has been made by the patient and physician not to pursue restoration of sinus rhythm by any means, including catheter or surgical ablation

The ACC/AHA/ACCP/HRS and ESC guidelines both advise that the following terms are no longer used:[1]​​[2]​

  • Valvular/non-valvular AF: the term valvular/non-valvular AF has been used to differentiate patients with AF in the presence/absence of moderate or severe mitral stenosis or a prosthetic heart valve. This terminology may be confusing and should be avoided

  • Lone AF: the term ‘lone AF’ has previously been used to identify AF in younger patients without structural heart disease. However, because definitions are variable, and all patients with AF have some form of pathophysiological basis, the term ‘lone AF’ is potentially confusing and should not be used

  • Chronic AF: guidelines now advise that the term ‘chronic AF' should be abandoned, as it has variable definitions

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