Indications for Atropine
Atropine is indicated for symptomatic bradycardia with hemodynamic compromise (heart rate <50 bpm with hypotension, ischemia, or ventricular arrhythmias), ventricular asystole, symptomatic AV nodal block, and as an antidote for organophosphate or muscarinic mushroom poisoning. 1, 2
Primary Cardiovascular Indications
Symptomatic Bradycardia
- Atropine is indicated when heart rate falls below 50 bpm accompanied by hypotension, low cardiac output, peripheral hypoperfusion, or frequent premature ventricular contractions. 1
- The drug is most effective when administered within 6 hours of acute MI onset, particularly with inferior MI or right coronary artery involvement. 1
- Atropine effectively treats profound sinus bradycardia with hypotension associated with thrombolytic therapy, especially involving the right coronary artery. 3
- It reverses bradycardia and hypotension following nitroglycerin administration, with a recommended dose of 0.5 mg IV every 5 minutes up to a maximum total dose of 2 mg. 1
Atrioventricular Block
- Atropine is indicated for symptomatic Type I (Mobitz I) second-degree AV block occurring at the AV nodal level, particularly with acute inferior MI. 1
- It is appropriate for third-degree AV block at the AV node level with narrow-complex escape rhythm, using 0.5 mg IV every 5 minutes up to a maximum total dose of 2 mg. 1
- Atropine is contraindicated for infranodal AV block (Type II second-degree or third-degree block with wide QRS complex), as this represents bundle branch disease requiring pacing, not atropine. 1, 3
Cardiac Arrest
- Atropine is indicated for ventricular asystole at a dose of 1 mg IV, repeated every 3-5 minutes if asystole persists during CPR. 1, 2
- Confirm asystole in two ECG leads before treating, as fine ventricular fibrillation may appear as asystole. 1
Toxicological Indications
Organophosphate and Muscarinic Poisoning
- Atropine is the antidote of choice for organophosphate nerve agent and insecticide intoxication, as well as muscarinic mushroom poisoning. 2, 4
- Initial dosing for poisoning is 2-3 mg IV, repeated every 20-30 minutes as needed. 2
- For patients with proven allergy to atropine, an acceptable alternative is glycopyrrolate combined with benzodiazepines or scopolamine. 4
Adjunctive Indications
Antisialagogue Effects
- Atropine serves as an antisialagogue for nausea and vomiting associated with morphine administration in acute MI, with an initial dose of 0.5-1 mg IV. 1, 2
- The FDA approves atropine for temporary blockade of severe or life-threatening muscarinic effects. 2
Critical Dosing Considerations
Standard Dosing Protocol
- Use 0.5 mg IV every 5 minutes up to a maximum total dose of 2 mg for bradycardia. 1, 3
- Never administer doses less than 0.5 mg IV, as this can cause paradoxical bradycardia through central reflex vagal stimulation or peripheral parasympathomimetic effects. 1, 5
- For patients with coronary artery disease, limit total dose to 0.03-0.04 mg/kg to avoid detrimental cardiac effects from tachycardia-induced ischemia. 2, 5
- Cumulative doses exceeding 2.5 mg over 2.5 hours increase risk of ventricular tachycardia/fibrillation, CNS toxicity, and sustained sinus tachycardia. 1
Absolute Contraindications
- Do not use atropine for asymptomatic sinus bradycardia greater than 40 bpm without hypoperfusion or ventricular ectopy. 1, 3
- Avoid atropine for wide-complex bradycardia or high-grade AV block with bundle branch block, as this represents infranodal disease requiring pacing. 1
Critical Clinical Pitfalls
When Atropine Fails
- If bradycardia does not respond promptly to atropine, proceed immediately to transcutaneous or transvenous pacing rather than escalating atropine doses. 1
- Atropine should be used with caution in acute MI due to the protective effect of parasympathetic tone against ventricular fibrillation and myocardial infarct extension. 3