Atrial fibrillation, commonly abbreviated AF or AFib, is a sustained cardiac arrhythmia characterised by chaotic electrical activity in the atria and an irregular ventricular rhythm when atrioventricular conduction is variable. Instead of a single organised impulse arising from the sinoatrial node and producing coordinated atrial contraction, numerous electrical wavelets or rapidly firing atrial sources produce disorganised activation. The atria therefore do not contract normally.
The atrioventricular node receives a large number of irregular impulses and allows some to pass to the ventricles, producing the characteristic “irregularly irregular” ventricular rhythm. Atrial fibrillation is one of the most common sustained arrhythmias and becomes more prevalent with increasing age and cardiovascular risk. It can occur in people with structural heart disease but can also occur in people without obvious major structural abnormalities.
AF can be classified according to its temporal pattern. Paroxysmal AF consists of episodes that begin and end spontaneously, commonly within seven days. Persistent AF lasts longer than seven days or requires intervention to restore sinus rhythm. Long-standing persistent AF refers to continuous AF lasting at least 12 months when rhythm control is still being pursued, while permanent AF describes a shared decision not to pursue further attempts to restore or maintain sinus rhythm.
These classifications describe the clinical course rather than different diseases. AF can also be asymptomatic or symptomatic, and symptom severity does not necessarily correspond to the duration or burden of the arrhythmia. A person may have intermittent AF that is detected incidentally, while another may experience severe palpitations during relatively brief episodes.
The loss of coordinated atrial contraction has physiological consequences. During normal sinus rhythm, atrial contraction contributes to ventricular filling, particularly when ventricular relaxation is impaired. In AF, this “atrial kick” is lost, which can reduce ventricular filling in susceptible people. Rapid and irregular ventricular activation can also reduce filling time and create variable stroke volume, potentially producing fatigue, breathlessness, dizziness or palpitations. More importantly, blood flow within the fibrillating atria, particularly the left atrial appendage, can become relatively stagnant.
This promotes thrombus formation in susceptible patients. If an atrial thrombus embolises, it can travel through the arterial circulation and cause an ischaemic stroke or systemic embolism. Stroke prevention is therefore a central component of AF management and is considered separately from decisions about controlling the heart rate or restoring sinus rhythm.
Diagnosis of AF generally requires documentation of the arrhythmia on an electrocardiogram or appropriate rhythm recording. On an ECG, typical AF lacks consistent P waves representing organised atrial depolarisation and shows an irregularly irregular ventricular response. A short standard ECG can confirm AF when the rhythm is present at the time of recording, but intermittent episodes may require ambulatory monitoring.
Devices such as wearable ECG monitors can sometimes detect episodes, although clinically important diagnoses should be confirmed using appropriate medical assessment. A pulse that feels irregular can raise suspicion but cannot establish AF on its own. Distinguishing AF from atrial flutter, frequent ectopic beats and other irregular rhythms is important because their mechanisms and management differ.
AF has important associations with stroke and other cardiovascular outcomes. Stroke risk varies between individuals according to factors such as age, previous stroke or transient ischaemic attack, hypertension, diabetes, heart failure and vascular disease. Clinical risk scores, including CHA₂DS₂-VASc or locally recommended alternatives, are used to structure assessment, although guidelines differ in some details and recommendations evolve. Anticoagulant medicines reduce the risk of thromboembolic stroke in people for whom anticoagulation is indicated.
They do not directly restore normal rhythm; their purpose is to reduce clot formation. Direct oral anticoagulants are commonly used in many patients, while warfarin remains important in particular circumstances such as mechanical heart valves and some forms of valvular disease. The decision balances thromboembolic risk against bleeding risk and other individual factors.
AF management has two major rhythm-related strategies: rate control and rhythm control, alongside stroke prevention and treatment of underlying cardiovascular risk factors. Rate control aims to prevent the ventricles from beating excessively rapidly, commonly using medicines such as beta blockers or selected calcium-channel blockers, depending on the patient's circumstances. Rhythm control aims to restore or maintain sinus rhythm using cardioversion, anti-arrhythmic medicines or catheter ablation when appropriate.
Catheter ablation commonly targets areas around the pulmonary veins because abnormal electrical activity originating there can initiate AF. Contemporary management increasingly considers rhythm control earlier in selected patients, particularly when symptoms or cardiovascular consequences make maintaining sinus rhythm desirable. The appropriate strategy depends on symptoms, AF duration, structural heart disease, age, comorbidities, patient preferences and procedural suitability.
AF frequently occurs alongside hypertension, coronary artery disease, heart failure, obesity, diabetes, sleep apnoea and valvular heart disease. These conditions can promote atrial enlargement, fibrosis, inflammation and electrical remodelling, creating a substrate that allows AF to initiate and persist. Alcohol can precipitate episodes in susceptible individuals, while hyperthyroidism can promote AF through increased sympathetic activity and altered electrophysiology. Acute illness, infection and postoperative states can also trigger AF. Treating associated risk factors is therefore part of AF management. Weight management, blood-pressure control, treatment of sleep apnoea where present, diabetes management, reduction of excessive alcohol intake and management of other cardiovascular disease can reduce AF burden or improve outcomes in appropriate patients.
Atrial fibrillation is not simply an irregular heartbeat and should not be dismissed as harmless because some episodes are brief or asymptomatic. Its defining feature is disorganised atrial electrical activation with an irregular ventricular response, and its major clinical consequences include symptoms, reduced cardiac efficiency and increased thromboembolic risk. Some episodes terminate spontaneously, while others persist and require intervention. Diagnosis requires rhythm documentation, and treatment is individualised around stroke prevention, symptom control, rate or rhythm management and treatment of underlying risk factors. AF can coexist with other arrhythmias and cardiovascular disease, so a comprehensive assessment is required rather than treating the irregular pulse alone.
