C. Intravenous diltiazem or metoprolol

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The patient’s heart rate is significantly elevated in the setting of atrial fibrillation, and he is hemodynamically stable; thus, slowing his heart rate with nondihydropyridine calcium channel blockers (diltiazem, verapamil) or beta-blockers is reasonable. Converting his rhythm to sinus is not the initial approach in a hemodynamically-stable patient (amiodarone, ibutilide or direct current cardioversion). Further investigations need to be performed first to determine the etiology prior to restoring sinus rhythm if clinically indicated. Digoxin alone is not generally recommended to lower heart rates in atrial fibrillation and is best used when systolic heart failure is present, but along with beta-blockers.

2. D. Intravenous diltiazem or metoprolol
The initial management in a hemodynamically-stable patient with uncontrolled heart rates from atrial fibrillation is a nondihydropyridine calcium channel blockers (diltiazem, verapamil) or beta-blocker. If heart failure is present, caution is advised until the systolic function (ejection fraction) is known.

Amiodarone to restore sinus rhythm (rhythm control strategy) is not appropriate in a stable patient when rate controlling has not even been attempted. This drug has many toxicities (see amiodarone toxicity) and should be avoided if possible.

Emergent direct current cardioversion is reserved for hemodynamically-unstable patients (hypotension, chest pain, end-organ hypoperfusion).

Digoxin alone is not recommended for initial therapy due to less efficacy to lower the heart rate and possible toxicities. If systolic dysfunction is present, it would be a reasonable choice. Digoxin is also frequently used in combination with nondihydropyridine calcium channel blockers (diltiazem, verapamil) or beta-blockers, if they fail to control the heart rate.

Flecainide 300 mg orally once can be used in “lone atrial fibrillation” patients (no structural heart disease or coronary artery disease); however, this is not a good initial management strategy until further testing (echocardiography, stress testing) has been performed. Flecainide and other class IC antiarrhythmic drugs must be given in combination with an AV blocking drug (nondihydropyridine calcium channel blockers, beta-blockers or digoxin) in order to prevent rapid conduction of atrial activity through the AV node to the ventricles (because class IC drugs increase AV nodal conduction).

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