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Atrial fibrillation (AF) is characterized by disorganized, rapid, and irregular atrial activation with loss of atrial contraction and with an irregular ventricular rate that is determined by AV nodal conduction (Fig. 246-1). In an untreated patient, the ventricular rate also tends to be rapid and variable, between 120 and 160 beats/min, but in some patients, it may exceed 200 beats/min. Patients with high vagal tone or AV nodal conduction disease may have slow ventricular rates.
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AF is the most common sustained arrhythmia and is a major public health problem. Prevalence increases with age, and >95% of AF patients are >60 years of age. The prevalence by age 80 is ~10%. The lifetime risk of developing AF for men 40 years old is ~25%. AF is slightly more common in men than women and more common in whites than blacks. Risk factors for developing AF in addition to age and underlying cardiac disease include hypertension, diabetes mellitus, cardiac disease, obesity, and sleep apnea. AF is associated with a 1.5- to 1.9-fold increased risk of mortality after controlling for underlying heart disease. AF is also associated with a risk of developing heart failure and vice-versa—patients with heart failure have an increased risk of developing AF. AF increases the risk of stroke by fivefold and is estimated to be the cause of 25% of strokes. It also increases the risk of dementia and silent strokes detected by MRI. Since AF is a marker for other predictors of mortality and morbidity, such as the severity of heart disease, it is difficult to determine the extent to which AF itself contributes to associated increased mortality and morbidity.
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AF is occasionally associated with an acute precipitating factor such as hyperthyroidism, acute alcohol intoxication, or an acute illness such as myocardial infarction or pulmonary embolism. AF occurs in up to 30% of patients recovering from cardiac surgery, associated with inflammatory pericarditis.
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The clinical pattern of AF suggests the underlying pathophysiology (Fig. 246-1). Paroxysmal AF is defined by episodes that start spontaneously and stop within 7 days of onset. Paroxysmal AF is often initiated by small reentrant or rapidly firing foci in sleeves of atrial muscle that extend into the pulmonary veins (PV). Catheter ablation that isolates these foci usually abolishes paroxysmal AF, although some ...