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Atrial fibrillation (AFib) is the most common arrhythmia, or problem with the heartbeat’s rate or rhythm.

AFib happens when rapid, disorganized electrical signals cause the heart’s two upper chambers (the atria) to fibrillate, or contract in a very fast and irregular fashion. During atrial fibrillation, the upper chambers contract so quickly that the atrial walls quiver.

AFib doesn’t always cause symptoms, but some people feel heart palpitations, chest pain, shortness of breath, and weakness.

AFib may result from damage to the heart’s electrical system, typically from other conditions that affect the heart, such as coronary artery disease or high blood pressure.

But when doctors can’t find any underlying heart disease -- which happens in at least 10% of AFib cases -- other factors may be at play. These include: too much caffeine or alcohol, stress, electrolyte or metabolic imbalances, drugs, severe infections, or genetic factors.

Sometimes, the cause of AFib is unknown.

Risk Factors for Atrial Fibrillation

Age: AFib risk increases with age, especially after 60. As people grow older, they’re more likely to develop heart disease and other conditions that can cause AFib.

Heart disease: Many heart problems raise the risk of AFib, including coronary artery disease, heart valve disease, rheumatic heart disease, heart failure, cardiomyopathy (weakened heart muscle), heart birth defects, and pericarditis (inflammation of the membrane or sac around the heart). Sick sinus syndrome can also raise the risk. With this condition, the heart’s electrical signals misfire and the heart rate alternates between fast and slow. AFib can also happen during a heart attack or after heart surgery. AFib is the most common complication after heart surgery, occurring in approximately 20%-30% of postoperative patients.

High blood pressure: Longstanding, uncontrolled high blood pressure is a common cause of AFib.

Lung disease: The risk of AFib increases if a person has lung disease, such as chronic obstructive pulmonary disease ( COPD) or emphysema. Risk also rises with pulmonary embolism, a blood clot in the lung.

Hyperthyroidism: An overactive thyroid gland can cause AFib.

Other health conditions: Obesity, diabetes, and metabolic syndrome raise the risk of AFib, perhaps because these conditions can lead to heart disease and other health problems. There’s also evidence that sleep apnea might heighten AFib risk.

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