Atrial fibrillation

Atrial fibrillation, also known as AF, AFib, or A-fib, is a heart rhythm disorder where the upper chambers (atria) beat rapidly and irregularly. The condition often starts with brief episodes of abnormal beating that gradually become longer or constant over time. It can also begin as another arrhythmia, such as atrial flutter, which then transforms into AF. This is the most common serious abnormal heart rhythm, affecting over 33 million people globally as of 2020.

Some people experience no symptoms during episodes. When symptoms do occur, they can include heart palpitations, fainting, lightheadedness, loss of consciousness, or shortness of breath. AF raises the risk of heart failure, dementia, and stroke. It is classified as a type of supraventricular tachycardia.

The arrhythmia often stems from rapid bursts of electrical activity originating in muscle bundles that extend from the atria into the pulmonary veins. A procedure called pulmonary vein isolation, using transcatheter ablation, can restore normal sinus rhythm. Other sources of AF include the autonomic ganglia of the heart (ganglionated plexi), the left atrial appendage, and the ligament of Marshall; these areas are sometimes targeted during ablation as well. As AF becomes more persistent, the junction between the pulmonary veins and the left atrium becomes less of a trigger, and the left atrium itself starts generating the arrhythmia independently.

The most common modifiable risk factors for AF are high blood pressure and valvular heart disease. Other heart-related risks include heart failure, coronary artery disease, cardiomyopathy, and congenital heart disease. In low- and middle-income countries, valvular heart disease often results from rheumatic fever. Lung-related risk factors include COPD, obesity, and sleep apnea. Emotional stress and biomarkers like cortisol may also play a role in its development. Additional risk factors include excess alcohol intake, tobacco smoking, diabetes, subclinical hypothyroidism, and thyrotoxicosis. However, about half of all cases occur without any of these known risks.

Healthcare providers may suspect AF by feeling a patient’s pulse and confirm it with an electrocardiogram (ECG). A typical ECG in AF shows irregularly spaced QRS complexes with no P waves. Healthy lifestyle changes—such as weight loss for those with obesity, increased physical activity, and reduced alcohol intake—can lower the risk of AF and lessen its impact. Treatment often involves medications to slow the heart rate (rate control) or to restore normal rhythm (rhythm control). Electrical cardioversion can convert AF to a normal rhythm and is often used in emergencies if the person is unstable. Ablation may prevent recurrence in some cases.

For people at low risk of stroke, blood-thinning medications are not necessarily required, though some providers may still prescribe them. Most people with AF are at increased risk of stroke, and for those at more than low risk, anti-clotting medications like warfarin or direct oral anticoagulants are generally recommended. These drugs reduce stroke risk but increase the chance of major bleeding.

The incidence and prevalence of AF are rising. In Europe and North America, it affects about 2 to 3% of the population (as of 2014). In the developing world, about 0.6% of males and 0.4% of females are affected. The condition becomes more common with age: it affects 0.1% of people under 50, 4% of those between 60 and 70, and 14% of those over 80. The first known report of an irregular pulse was by Jean-Baptiste de Sénac in 1749, and Thomas Lewis was the first to document it using an ECG in 1909.

Symptoms often relate to a rapid heart rate, which may feel like palpitations, a racing or skipping heartbeat, or exercise intolerance. Other possible signs include fatigue, shortness of breath, swelling (from congestive heart failure), or loss of consciousness due to insufficient blood flow to the brain. Sometimes AF is only discovered after a stroke or transient ischemic attack (TIA), or during a routine physical exam or ECG. Because most cases are secondary to other medical issues, chest pain, signs of hyperthyroidism (like weight loss and diarrhea), or lung disease symptoms may point to an underlying cause. A history of stroke, TIA, high blood pressure, diabetes, heart failure, or rheumatic fever can indicate a higher risk of complications. The rapid, uncoordinated heart rate can reduce cardiac output, leading to inadequate oxygen delivery. Common symptoms of uncontrolled AF include shortness of breath when upright or lying flat, dizziness, and sudden nighttime shortness of breath (paroxysmal nocturnal dyspnoea), which may progress to leg swelling from congestive heart failure.