Understanding atrial fibrillation: symptoms, stroke risk and treatment

What atrial fibrillation is

Normally the heart beats in a coordinated rhythm set by its natural pacemaker. In atrial fibrillation, the upper chambers (the atria) fire chaotically instead of contracting properly, so the heartbeat becomes irregular and often fast. Some people feel palpitations, breathlessness, tiredness or dizziness; others feel nothing at all and AF is found by chance. It can be occasional (paroxysmal), persistent, or permanent. Because it can be silent, AF sometimes announces itself only when it causes a stroke.

Why AF raises stroke risk

This is the crucial point. When the atria quiver rather than contract, blood can pool and form a clot, particularly in a small pouch called the left atrial appendage. If a clot breaks off, it can travel to the brain and cause a stroke — and AF-related strokes tend to be more severe than average. This is why, for most people with AF, preventing stroke is the single most important part of treatment, and why AF is worth detecting even when it causes few symptoms.

How it is detected and assessed

AF is diagnosed with an ECG, sometimes needing prolonged monitoring (a 24-hour tape or a longer wearable monitor) to catch intermittent episodes; a simple pulse check can first raise suspicion. Once confirmed, the assessment has two strands: estimating stroke risk using a score such as CHA₂DS₂-VASc, and estimating bleeding risk (for example with HAS-BLED) before starting blood-thinning treatment. These scores guide, but do not replace, an individual discussion about the balance of benefit and risk.

The two goals of treatment

AF treatment has two separate aims. The first, and usually most important, is stroke prevention with anticoagulation ("blood thinners") for those at sufficient risk — modern direct oral anticoagulants (DOACs) or warfarin substantially reduce stroke risk. The second is managing the rhythm itself: "rate control" (slowing a fast heart rate with medicines so the heart works comfortably) or "rhythm control" (restoring or maintaining normal rhythm with medicines, electrical cardioversion, or a procedure called ablation). Which rhythm strategy suits a person depends on their symptoms, age and heart. Crucially, controlling symptoms does not remove the need for stroke prevention — the two goals are managed separately.