Scientists don't fully understand the basic problems behind atrial fibrillation (AF), but they do know many of the factors that increase the risk of AF.
Age is an important factor; AF is uncommon before age 50, but it affects nearly 8% of men between 65 and 74 and almost 12% between 75 and 84. Gender is also important; AF occurs about 50% more frequently in men than women. Since about a third of all patients with AF have a family history of the disorder, heredity also plays a role, and several specific genetic abnormalities have already been identified.
Cardiovascular conditions are strongly linked to AF. The three most important are high blood pressure, heart valve disorders (particularly mitral valve problems), and coronary artery disease (with or without a heart attack). Heart failure, a debilitating problem that occurs when the weakened heart muscle is unable to pump blood effectively, is another risk factor for AF. Less often, inflammation in the membrane around the heart (pericarditis) triggers AF.
Lung disorders also increase the risk of AF. Culprits include chronic obstructive lung disease, blood clots in the lungs (pulmonary emboli), and pneumonia. Chest surgery is another cause.
A wide variety of medical conditions are associated with AF. An overactive thyroid gland (hyperthyroidism) is the best known; it's what sent President George H.W. Bush into AF (and into the Bethesda Naval Hospital) in 1991, and even high-normal thyroid activity predisposes one to AF. Diabetes and obesity increase risk, as do medications such as bronchodilators used for asthma and COPD, decongestants, steroids, and nonsteroidal anti-inflammatory drugs.
Behavioral factors are also tied to AF. Always a villain, smoking is on the hit list. Moderate drinking does not lead to AF, but excessive alcohol consumption does, particularly in the setting of binge drinking. Anger and hostility boost the risk of AF in men. Surprisingly, perhaps, caffeine does not appear to be a risk factor.
Although vigorous exercise sometimes triggers AF in young men, walking and other moderate physical activities provide long-term protection. Some studies suggest that taking statin drugs or eating fish may reduce the risk of AF over the long run, while others do not. Beta blockers, ACE inhibitors, and angiotensin-receptor blockers (ARBs) appear to reduce the risk of AF in patients with hypertension.
There are several ways to categorize AF. In one system, it's called primary AF when the problem originates in the heart itself, and secondary AF when it results from a noncardiac medical condition, in which case the AF often resolves when the underlying problem is corrected. When primary AF occurs in a structurally normal heart, it is called lone AF, which carries a relatively low risk of complications. Other types of primary AF, however, can be more troublesome.
Another classification system for AF depends on the frequency and duration of the arrhythmia:
paroxysmal AF — recurrent episodes of AF that end within seven days without treatment. Most bouts of paroxysmal AF end in less than 24 hours, but even though episodes are brief, patients are still at risk of stroke.
persistent AF — episodes that last longer than seven days or require treatment to convert back to a normal heart rhythm. The longer an episode lasts, the harder it is to restore a normal rhythm.
permanent AF — AF that has lasted longer than a year.