What drug is best for initial treatment of rapid atrial fib?

According to the results of this study it's good old, tried-and-true diltiazem:

Measurements and Main Results: The primary end point was sustained VR control (less than 90 bpm) within 24 hours; the secondary end points included AF symptom improvement and length of hospitalization. At 24 hours, VR control was achieved in 119 of 150 patients (79%). The time to VR control was significantly shorter among patients in the diltiazem group (log-rank test, p less than 0.0001) with the percentage of patients who achieved VR control being higher in the diltiazem group (90%) than the digoxin group (74%) and the amiodarone group (74%). The median time to VR control was significantly shorter in the diltiazem group (3 hours, 1-21 hours) compared with the digoxin (6 hours, 3-15 hours, p less than 0.001) and amiodarone groups (7 hours, 1-18 hours, p = 0.003). Furthermore, patients in the diltiazem group persistently had the lowest mean VR after the first hour of drug administration compared with the other two groups (p less than 0.05). The diltiazem group had the largest reduction in AF symptom frequency score and severity score (p less than 0.0001). In addition, length of hospital stay was significantly shorter in the diltiazem group (3.9 ± 1.6 days) compared with digoxin (4.7 ± 2.1 days, p = 0.023) and amiodarone groups (4.7 ± 2.2 days, p = 0.038).

There was no difference in adverse hemodynamic effects. A surprising finding in the study was that there was no difference in conversion to sinus rhythm. From an electrophysiologic perspective amiodarone would be expected to have some efficacy in achieving sinus rhythm whereas diltiazem and digoxin would not. The authors point out, though, that this was a rate control study and amiodarone was not used in doses optimized for conversion to sinus rhythm. A significant caveat is these were low risk patients:

The main exclusion criteria were VR greater than 200 bpm; pre-excitation syndrome; hypotension (systolic blood pressure less than 90 mm Hg); congestive heart failure; presence of implanted pacemaker and/or implantable cardioverter defibrillator; recent myocardial infarction; unstable angina; stroke or thromboembolism within the past 6 months; allergy or contraindication to the study medications; use of antiarrhythmic and/or atrioventricular nodal blocking drug within last 7 days (in case of amiodarone, within past 3 months); or other major medical conditions including renal failure, respiratory failure, and bleeding disorders.

H/T to The Hospitalist.