What is the initial medication for symptomatic bradycardia?

Management of Symptomatic Bradycardia

Atropine is the initial medication of choice for symptomatic bradycardia, administered at a dose of 0.5-1 mg IV, repeated every 3-5 minutes as needed up to a maximum total dose of 3 mg. 1, 2

Initial Assessment and Treatment Algorithm

• Evaluate if bradycardia is causing symptoms or hemodynamic compromise (altered mental status, ischemic chest discomfort, acute heart failure, hypotension, or other signs of shock) 1
• Administer atropine 0.5-1 mg IV for symptomatic bradycardia 1, 2
• Repeat atropine every 3-5 minutes as needed up to a maximum total dose of 3 mg 1, 2
• Avoid doses of atropine <0.5 mg as they may paradoxically worsen bradycardia 1, 3

Mechanism and Indications

• Atropine is a muscarinic antagonist that blocks parasympathetic (cholinergic) activity, reversing decreases in heart rate, systemic vascular resistance, and blood pressure 2, 3
• Atropine is indicated for symptomatic sinus bradycardia (heart rate <50 bpm with hypotension, ischemia, or escape ventricular arrhythmia), ventricular asystole, and symptomatic AV block at the nodal level 3, 2

Second-Line Treatment Options

• If bradycardia persists despite atropine, initiate IV infusion of β-adrenergic agonists 1:
  • Dopamine (2-10 μg/kg/min)
  • Epinephrine (2-10 μg/min)
• Consider transcutaneous pacing in unstable patients who do not respond to atropine 1, 3
• Prepare for transvenous pacing if the patient does not respond to drugs or transcutaneous pacing 1

Special Considerations and Pitfalls

• Atropine is most effective for sinus bradycardia occurring within 6 hours of onset of symptoms of acute MI 3
• Atropine may be ineffective in type II second-degree or third-degree AV block with new wide-QRS complex where the block is likely in non-nodal tissue 1, 4
• Avoid atropine in heart transplant patients without evidence of autonomic reinnervation, as it may cause paradoxical high-degree AV block 1
• Use atropine cautiously in inferior myocardial infarction as increased heart rate may worsen ischemia or increase infarction size 1, 5
• Atropine should not delay implementation of external pacing for patients with poor perfusion 1
• Excessive doses of atropine (>3 mg) may cause central anticholinergic syndrome, including confusion, agitation, and hallucinations 1

Efficacy and Response Rates

• Approximately 50% of patients with hemodynamically compromising bradycardia respond to atropine with either partial or complete improvement 6
• Patients with bradycardia are more likely to respond to a single dose and lower total dose of atropine compared to patients with AV block 6
• Adverse responses to atropine are uncommon but may include ventricular tachycardia, ventricular fibrillation, sustained sinus tachycardia, increased premature ventricular contractions, and toxic psychosis 5
• Serious adverse effects necessitate careful medical supervision during atropine administration 5

Monitoring and Follow-up

• Continue cardiac monitoring during and after treatment 1
• Evaluate response to therapy by monitoring heart rate, blood pressure, and resolution of symptoms 1
• If normal sinus rhythm is achieved during prehospital care, it is likely to be maintained through ED discharge 6, 7