Atrial fibrillation, the most common sustained clinical arrhythmia, is diagnosed by the finding of an irregularly irregular ventricular rhythm without discrete P waves (Figure 12–1). The QRS complex is usually narrow, but it may be wide if aberrant conduction or bundle branch block is present. Atrial fibrillation associated with the Wolff-Parkinson-White syndrome may result in very rapid ventricular rates due to conduction of atrial impulses over an accessory pathway and may be life-threatening. This arrhythmia is diagnosed by its very rapid, irregular rate associated with wide, preexcited QRS complexes, and requires emergency treatment (see later section, Long-Term Approach).
The 12-lead electrocardiogram shows the typical rapid irregular rhythm seen with atrial fibrillation.
Approximately 4% of the population over age 60 years has sustained an episode of atrial fibrillation, with a particularly steep increase in prevalence after the seventh decade of life. Other risk factors besides age for development of atrial fibrillation include heart failure, hypertensive cardiovascular disease, coronary artery disease, valvular heart disease, chronic lung disease, thyroid disease, and alcohol consumption. Moreover, both sustained and paroxysmal atrial fibrillation can cause clot formation and embolism, most often clinically manifest by the development of a cerebrovascular accident (CVA) or other systemic emboli. It is estimated that 15–20% of CVAs in nonrheumatic patients are due to atrial fibrillation.
Symptoms associated with atrial fibrillation are often related to the irregularity of the rhythm and loss of atrial contraction. Common symptoms include palpitations, shortness of breath at rest or with exertion, and lightheadedness. Other nonspecific symptoms, including chest pain or generalized fatigue, can be manifestations of atrial fibrillation and add to the difficulty in diagnosing the abnormal cardiac rhythm based on symptoms alone.
When called on to manage new-onset atrial fibrillation, it is important to establish the precipitating factors, because the type of associated condition determines long-term prognosis. In some patients, episodes of atrial fibrillation may be initiated by alcohol or drug use. Atrial fibrillation may result from acute intercurrent ailments. For example, this arrhythmia may develop in patients with hyperthyroidism or lung disease or after either cardiac or pulmonary surgery, especially in older patients. Atrial fibrillation is also seen in patients with acute pulmonary embolism, myocarditis, or acute myocardial infarction, particularly when the last condition is complicated by either occlusion of the right coronary artery or heart failure. When atrial fibrillation occurs in these settings, it almost always abates spontaneously if the patient recovers from the underlying problem. Hence, management usually involves administration of drugs to control the heart rate, and long-term antiarrhythmic therapy is generally not needed.