Initial atropine dose of 0.5 mg versus 1 mg in unstable bradycardia: A propensity score-matched retrospective cohort study.

BACKGROUND: The optimal initial intravenous atropine dose for unstable bradycardia remains uncertain. While American Heart Association guidelines recommend 1.0 mg, European Resuscitation Council algorithms recommend 0.5 mg. We compared the effectiveness of these two doses in emergency department patients with unstable bradycardia. METHODS: In this single-center retrospective cohort study, adults receiving intravenous atropine as first-line treatment for unstable bradycardia (heart rate < 50 beats/min with hypoperfusion signs) were grouped by initial dose (0.5 mg or 1.0 mg). Propensity score matching (1,1) was performed. The primary outcome was first-dose success, defined as heart rate > 50 beats/min within 3 min without additional atropine or rescue therapy. Secondary outcomes included additional atropine use, rescue therapy, intensive care unit admission, and in-hospital mortality. RESULTS: Of 355 screened patients, 242 were included; 174 remained after matching (87 per group). First-dose success was higher with 1.0 mg than with 0.5 mg (44.8% vs. 25.3%; p = 0.007). The 1.0 mg group required less additional atropine (26.4% vs. 48.3%; p = 0.003), less rescue therapy (50.6% vs. 73.6%; p = 0.002), and had fewer intensive care unit admissions (52.9% vs. 73.6%; p = 0.005). Mortality was similar (3.4% vs. 4.6%, p = 1.000). In multivariable analysis, a 1.0 mg dose (aOR 2.42, 95% CI 1.25-4.68; p = 0.008) and sinus node dysfunction (aOR 3.85, 95% CI 1.95-7.60; p < 0.001) independently predicted first-dose success. CONCLUSIONS: An initial atropine dose of 1.0 mg was associated with higher first-dose success and less treatment escalation than 0.5 mg in adults with unstable bradycardia. Prospective multicenter studies are needed to confirm these findings.