- Irregularly irregular rhythm.
- Absence of P waves on the electrocardiogram.
Atrial fibrillation, the most common sustained clinical arrhythmia, is diagnosed by finding an irregularly irregular ventricular rhythm
without discrete P waves (Figure 21–1).
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 occur with very
rapid ventricular rates 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 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. Risk factors
for development of atrial fibrillation include heart failure, hypertensive
cardiovascular disease, coronary artery disease, and valvular heart
disease. Moreover, both sustained and paroxysmal atrial fibrillation
have important implications for 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.
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 caffeine,
alcohol, or marijuana 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.
Alternatively, atrial fibrillation may occur in association with structural cardiac disease. Important associated conditions include
rheumatic mitral stenosis, hypertension, hypertrophic cardiomyopathy,
or chronic heart failure. In contrast to patients with acute intercurrent
ailments, those with structural heart disease may expect (even with
antiarrhythmic therapy) many recurrences and chronic atrial fibrillation
Lone fibrillation is the term used to describe patients with atrial fibrillation not associated with known cardiac conditions
or noncardiac precipitants. The natural history of the atrial fibrillation
for those with lone atrial fibrillation is similar to that in patients
with structural cardiac disease, in that episodes of atrial fibrillation
are likely to recur and, eventually, the arrhythmia may become sustained.