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Industry: Email Alert RSS FeedAcute Management of Atrial Fibrillation: Part I. Rate and Rhythm Control
American Family Physician, July 15, 2002 by Dana E. King, Lori M. Dickerson, Jonathan L. Sack
Beta blockers and calcium channel blockers are the drugs of choice because they provide rapid rate control.(4,7,12) These drugs are effective in reducing the heart rate at rest and during exercise in patients with atrial fibrillation.(4,7,12) Factors that should guide drug selection include the patient's medical condition, the presence of concomitant heart failure, the characteristics of the medication, and the physician's experience with specific drugs.
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Compared with beta blockers and calcium channel blockers, digoxin is less effective for ventricular rate control, particularly during exercise. Digoxin is most often used as adjunctive therapy because of its slower onset of action (usually 60 minutes or more) and its weak potency as an atrioventricular node- blocking agent.(3,13) It can be used when rate control during exercise is of less concern.(4,7,12) Digoxin is a positive inotropic agent, which makes it especially useful in patients with systolic heart failure.(7)
The calcium channel blockers diltiazem (Cardizem) and verapamil (Calan, Isoptin) are effective for initial ventricular rate control in patients with atrial fibrillation. These agents are given intravenously in bolus doses until the ventricular rate becomes slower.(7) Dihydropyridine calcium channel blockers (e.g., nifedipine [Procardia], amlodipine [Norvasc], felodipine [Plendil], isradipine [DynaCirc], nisoldipine [Sular]), are not effective for ventricular rate control.
Physicians can use the "rule of 15" in administering diltiazem to patients weighing 70 kg (154 lb): first, give 15 mg intravenously over two minutes, repeat the dose in 15 minutes if necessary, and then start an intravenous infusion of 15 mg per hour; titrate the dose to control the ventricular rate (5 to 15 mg per hour). Verapamil, in a dose of 5 to 10 mg administered intravenously over two minutes and repeated in 30 minutes if needed, can also be used for initial rate control. Although all calcium channel blockers can cause hypotension, verapamil should be used with particular caution because of the possibility of prolonged hypotension as a result of the drug's relatively long duration of action.
Beta blockers such as propranolol (Inderal) and esmolol (Brevibloc) may be preferable to calcium channel blockers in patients with myocardial infarction or angina, but they should not be used in patients with asthma. As initial treatment, 1 mg of propranolol is given intravenously over two minutes; this dose can be repeated every five minutes up to a maximum of 5 mg. Maintenance dosing of propranolol is 1 to 3 mg given intravenously every four hours. Esmolol has an extremely short half-life and may be given as a continuous intravenous infusion to maintain rate control (Table 1).(3)
Despite depressive effects on contractility (unless the ejection fraction is below 0.20), calcium channel blockers and beta blockers can be used for initial ventricular rate control in patients with heart failure. Oxygen delivery to the heart is usually much improved once the ventricular rate is controlled (less than 100 beats per minute). A slower ventricular response rate also allows more filling time for the heart and, thus, improved cardiac output.(14) However, the benefits of long-term treatment with calcium channel blockers or beta blockers should be carefully weighed against the negative inotropic effects. Drugs for rate control can generally be stopped once sinus rhythm is restored.(3)
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