Excluding simple atrial premature depolarizations, atrial fibrillation is the most commonly encountered supraventricular arrhythmia. Its incidence rises dramatically after the fifth decade for both men and women, and it reaches an estimated prevalence of 9-12% in elderly men. As many as 1 million Americans may have chronic nonvalvular atrial fibrillation.
What cardiovascular diseases are likely to coexist in patients with atrial fibrillation?
Hypertensive heart disease is the most common preexisting condition; however, congestive heart failure (of various etiologies‚ ischemic, cardiomyopathic, etc.) and rheumatic heart disease are more potent risk factors for the development of atrial fibrillation. Patients without identifiable cardiovascular disease or other conditions associated with atrial fibrillation are said to have ‹“ ‹“lone atrial fibrillation.‚ An estimated 3-25% of all patients with chronic atrial fibrillation have lone atrial fibrillation.‚
Which agents are effective in slowing the ventricular response in acute atrial fibrillation?
Although frequently used as a first-line drug, digoxin is much less effective in acute rate control than other drugs. The onset of action for digoxin is slow, and it exerts its acute rate-slowing effects largely by an indirect vagotonic activity. Digoxin’s effect tends to vanish when patients increase their circulating catecholamine levels during exercise. Digoxin, however, does continue to be the agent of choice for rate control in patients with congestive heart failure or severe impairment of left ventricular function.
In contrast to digoxin, intravenous diltiazem (bolus of 20-25 mg and maintenance of 5-15 mg/hr) has an onset of action within minutes and is generally not associated with significant hypotension. Intravenous beta blockers (e.g., esmolol, 500 (ig/kg/min load, then 100 |j.g/kg/min; or propranolol, 1 mg over 1 min repeated 3-5 times, then start oral) are also effective and are the treatment of choice in atrial fibrillation associated with elevated catecholamine levels (i.e., postoperative patients).