This single-center retrospective cohort study compared initial IV atropine 0.5 mg vs. 1.0 mg as first-line treatment in adult ED patients with unstable bradycardia (HR <50 bpm with hypoperfusion signs), using propensity score matching (87 per group, n=174 after matching).
First-dose success (HR >50 bpm within 3 min, no rescue needed) was higher with 1.0 mg vs. 0.5 mg (44.8% vs. 25.3%; p=0.007). The 1.0 mg group also needed less additional atropine (26.4% vs. 48.3%), less rescue therapy (50.6% vs. 73.6%), and had fewer ICU admissions (52.9% vs. 73.6%). In-hospital mortality was similar (3.4% vs. 4.6%).
- Single-center retrospective design limits generalizability; residual confounding cannot be excluded despite propensity matching. - Success defined at 3 minutes may not capture clinically meaningful differences in hemodynamic trajectory. - Mortality was not different, so it is unclear whether the higher first-dose success rate translates to improved patient outcomes.
In adults with unstable bradycardia, starting with atropine 1.0 mg (per AHA guidelines) appears more effective than 0.5 mg at achieving rapid rate response and reducing need for rescue therapy. Clinicians following ERC protocols using 0.5 mg should be aware that treatment escalation may be more frequently required.
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