UMEM Educational Pearls

Background: The 2025 AHA guidelines changed their recommended initial IV atropine dose for unstable bradycardia from 0.5 mg to 1.0 mg, while the 2025 ERC guidelines continue to recommend an initial dose of 0.5 mg. A 2025 review found limited comparative studies and noted that using 0.5 mg as an initial dose seems “clinically reasonable" [1].

Now: One tertiary care center performed a retrospective propensity-score matched study [2] comparing the 2 groups of patients with unstable bradycardia who had received an initial dose of 0.5 mg versus 1 mg in their ED between 2020 and 2025.

• Primary outcome = First-Dose Success (reaching a heart rate >50 bpm within 3 minutes without additional therapy). 
• Notably excluded were patients with noncardiac secondary bradycardia (hyperkalemia, drowning, trauma, etc.) and those with pacemaker failure, amongst others.

Results in the propensity score-matched cohort:

• First-dose success was significantly higher in the 1.0 mg vs the 0.5 mg group (45 vs 25%; p=0.007)
  • NNT of 6 (95% CI, 3-18)
• The 1.0 mg group had lower rates of:
  • Additional atropine requirement (26 vs 48%, p=0.003)
  • Other rescue therapy requirement (51% vs 74%, p=0.002)
  • ICU admission (53% vs 74%, p=0.005).
• No difference between groups in 30-day mortality or subsequent permanent pacemaker placement

Bottom Line: Acknowledging the small size & retrospective nature of the study, it appears that an initial dose of 1mg IV atropine helps us work smarter--not harder--in the stabilization of patients with unstable bradycardia.

References

1. Yokose M, Sangawa M, Shiomi H, et al. Initial Dose of Intravenous Atropine for Patients With Symptomatic Bradycardia?- A Scoping Review. Circ Rep. 2025;7(11):1044-1050. Published 2025 Sep 27. doi:10.1253/circrep.CR-25-0169
2. Kokulu K, Sert ET, Akar EH, Gül M. Initial atropine dose of 0.5 mg versus 1 mg in unstable bradycardia: A propensity score-matched retrospective cohort study. Am J Emerg Med. Published online August 2, 2026. doi:10.1016/j.ajem.2026.07.065