Overall, diltiazem may be more effective than metoprolol in the acute management of AFib with RVR without increased side effects based on a few small but randomized double-blind studies.

A systematic review¹ based on 2 trials^2,3 comparing IV diltiazem with IV metroprolol in patients with atrial fibrillation seen in emergency departments has reported better acute rate control with IV diltiazem (RR 1.8 [95% CI, 1.2-1.6]).  In these studies, the onset of rate control was faster and the percentage decrease in ventricular rate at each time point was higher with IV diltiazem.  In general, 0.25 mg/kg of IV diltiazem (max 25 mg) and 0.15 mg/kg of IV metoprolol (max 10 mg) were used.

Exclusion criteria in these studies included severe congestive heart failure, hypotension, acute coronary syndrome, and use of either class of drugs within the past five days.

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References

1. Martindale JL, deSouza IS, Silverberg M et al.. Beta-blockers versus calcium channel blockers for acute rate control of atrial fibrillation with rapid ventricular response: a systematic review. Eur J Emerg Med 2015;22: 150-154. https://www.ncbi.nlm.nih.gov/pubmed/25564459
2. Demircan C, Cikriklar H, Engindeniz Z, et al. Comparison of the effectiveness of intravenous diltiazem and metoprolol in the management of rapid ventricular rate in atrial fibrillation. Emerg Med J 2005;22: 411-414. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1726824/pdf/v022p00411.pdf 
3. Fromm C, Suan SJ, Cohen V, et al. Diltizem vs metoprolol in the management of atrial fibrillation or flutter with rapid ventricular rate in the emergency department. J Emerg Med 2015;49:175-82. https://www.ncbi.nlm.nih.gov/pubmed/25913166

Contributed by William L. Hwang, MD, Mass General Hospital, Boston, MA.