Jul 25, 2025
ACLS/BLS Tips
ACLS/BLS Tips: Atropine
Atropine, a non-selective muscarinic antagonist (anticholinergic), is an integral drug within ACLS for the management of symptomatic bradycardia. By competitively inhibiting acetylcholine at muscarinic receptors, particularly the M2 subtype in the heart, atropine diminishes parasympathetic (vagal) tone, leading to increased firing of the sinoatrial node (increased heart rate) and enhanced atrioventricular (AV) nodal conduction. Therefore, Atropine is ideally suited for sinus bradyarrhythmias.
Clinically, atropine is administered intravenously in acute settings to counteract bradycardia, especially when accompanied by hemodynamic instability. The standard initial dose is 1 mg IV push, repeatable every 3 to 5 minutes, with a maximum total dose of 3 mg.
However, caution is warranted in certain scenarios. Atropine may be ineffective in cases of second-degree heart block type II and third-degree heart block with a low Purkinje or ventricular escape rhythm. Additionally, low doses (below 0.5 mg) can paradoxically induce bradycardia, possibly due to central vagal stimulation. Adverse effects such as dry mouth, blurred vision, urinary retention, and confusion, particularly in the elderly, necessitate careful patient monitoring.
Indications:
First line drug for symptomatic sinus bradycardia
May be beneficial in presence of AV nodal block (Note: not likely to be effective for second-degree type II or third-degree AV block, or a block in non-nodal tissue)
Dose:
1 mg IV every 3-5 min as needed to a maximum of 3 mg or 0.04 mg/kg
Caution:
Use with caution in presence of myocardial ischemia and hypoxia for the reason of increasing myocardial oxygen demand.
Unlikely to be effective for hypothermic bradycardia.
ACLS Tips
Bradycardia can lead to hemodynamic instability due to the decrease in heart rate. Remember, Cardiac Output (CO) = Heart Rate (HR) X Stroke Volume (SV), therefore a reduced HR can reduce CO and blood pressure. The ACLS algorithm indicates the use of bradycardia management (e.g., Atropine) when the HR is persistently less than 50 bpm with signs of hypotension and/or poor end-organ perfusion, such as:
Acutely altered mental status
Signs of shock
Ischemic chest discomfort
Acute heart failure
If your initial atropine did not yield the intended response you were looking for (increased HR), you can consider repeat doses to a max of 3mg, especially for sinus rhythms or if you had slight improvement with your initial dose. Otherwise, you can consider other bradycardia management interventions such as:
Epinephrine Infusion
Dopamine Infusion
Transcutaneous pacing.
References:
American Society of Health-System Pharmacists. (2024). Atropine monograph for professionals. Drugs.com. https://www.drugs.com/monograph/atropine.html
Heart & Stroke Foundation of Canada. (2020). Advanced Cardiac Life Support. Canada.
