atrial fibrillation
Imagine the two upper chambers of the heart, the atria, trembling like a bag of squirming worms instead of squeezing firmly. In atrial fibrillation the atria fire hundreds of times a minute in a disorganized swirl, so they never give a proper coordinated beat. The lower chambers respond at random intervals, which is why the pulse feels irregularly irregular.
Because the atria no longer empty completely, blood can pool and clot, especially in a small pouch called the left atrial appendage. A clot that breaks loose may travel to the brain and cause a stroke — the most feared complication. The rapid, irregular ventricular rate can also weaken the heart over time and provoke heart failure.
Atrial fibrillation is the most common sustained arrhythmia, rising sharply with age and with conditions such as high blood pressure, valve disease, obesity and sleep apnoea. Management has two strands: lowering stroke risk with anticoagulation guided by a risk score, and controlling the rhythm or rate with drugs or catheter ablation. It is not automatically dangerous in the short term, but the long-term stroke risk is what makes it matter.
A 72-year-old with high blood pressure is found to have an irregular pulse at a routine check; an ECG confirms atrial fibrillation, and after a risk assessment she is started on a direct oral anticoagulant to prevent stroke.
An incidentally found irregular pulse often turns out to be silent atrial fibrillation.
On the ECG, atrial fibrillation shows no clear P waves and an irregularly irregular QRS rhythm — a fingerprint that distinguishes it from the regular sawtooth of atrial flutter.