Written by Meghan Breed
IV diltiazem and IV metoprolol are two of the most common drugs used to treat hemodynamically stable atrial fibrillation with rapid ventricular response (RVR). Diltiazem achieved rate control more quickly than metoprolol (15 min vs. 30 min); however, there was no statistically significant difference between sustained rate control at 3 hours.
Why does this matter?
Atrial fibrillation is the most common sustained cardiac arrhythmia encountered in the ED. Timely and adequate treatment of the arrhythmia is important for patient care and disposition.
These drugs are trendy AF…
Data were gathered retrospectively by review of the electronic medical record. 573 patients were initially identified; however, only 51 patients were included, which means this was a very small study. Important exclusion criteria were initial HR>220bpm, SBP<90mmHg, receipt of both medications to achieve initial rate control, acute decompensated heart failure and, interestingly, lack of rate control at 30 minutes. The primary outcome of this study was sustained rate control, HR <100 bpm, for 3 hours from the time initial rate control – this was not statistically significant between the two groups: diltiazem 87.5% vs. metoprolol 78.9%, p = 0.45. As previously mentioned, subjects were excluded from this study if rate control was not achieved by 30 minutes. Diltiazem achieved initial rate control in about half the time it took metoprolol to achieve adequate rate control. However, this may have been confounded by the medication doses. Patients given diltiazem received a median dose of 0.24mg/kg (usual dose 0.25mg/kg) and only 6.3% of patients required a second dose. In contrast, patients receiving metoprolol received a median dose of 0.05mg/kg (usual dose 0.15mg/kg), and 42.1% of patients required repeat dosing. More patients in the diltiazem group had new-onset atrial fibrillation, whereas those in the metoprolol group tended to be on a beta-blocker at home, suggesting chronic atrial fibrillation. After initial rate control with IV medications, 75% of patients in the diltiazem group received PO medications (median administration time 168 minutes) and 68% in the metoprolol group received PO medications (median time to administration 80 minutes). Perhaps if we got PO medications on board more quickly, the rate of sustained rate control would increase. Notably, safety outcomes between the two groups were not significantly different.
Comparison of sustained rate control in atrial fibrillation with rapid ventricular rate: Metoprolol vs. Diltiazem. Am J Emerg Med. 2020 Dec 3;40:15-19. doi: 10.1016/j.ajem.2020.11.073. Online ahead of print.