What is the first-line treatment for an adult with symptomatic bradycardia?

First-Line Treatment for Symptomatic Bradycardia

Atropine 0.5–1 mg IV push is the first-line treatment for symptomatic bradycardia, repeated every 3–5 minutes as needed up to a maximum total dose of 3 mg. 1, 2, 3

Identifying Symptomatic Bradycardia

Before treating, confirm the patient has hemodynamic compromise, defined by any of the following 1, 2:

• Altered mental status or loss of consciousness 1
• Systolic blood pressure <80–90 mmHg 1, 2
• Signs of shock (poor perfusion, cold extremities, delayed capillary refill) 2
• Ischemic chest pain or worsening angina 1, 2
• Acute heart failure symptoms (dyspnea, pulmonary edema) 1, 2
• Frequent ventricular ectopy or escape rhythms 1

Critical caveat: Asymptomatic bradycardia—even with heart rate <40 bpm—requires no treatment and intervention is contraindicated. 1

Atropine Dosing Protocol

Initial Administration

• Give 0.5–1 mg IV push immediately when symptomatic bradycardia is recognized 1, 2, 3
• Repeat every 3–5 minutes as needed 1, 2, 3
• Maximum cumulative dose: 3 mg total (approximately 3–4 doses) 1, 2, 3

Critical Dosing Warning

Never administer doses <0.5 mg, as sub-therapeutic amounts cause paradoxical worsening of bradycardia through central parasympathomimetic effects. 1, 2, 4 This can precipitate ventricular standstill, particularly in patients with heart block. 5

When Atropine Will Work vs. When It Will Fail

Atropine Is Effective For (Nodal-Level Blocks):

• Sinus bradycardia 1, 2, 3
• First-degree AV block 1, 2
• Mobitz I (Wenckebach) second-degree AV block 1, 2
• Vagally-mediated bradycardia (e.g., during airway manipulation) 2

Atropine Is Ineffective or Harmful For (Infranodal Blocks):

• Mobitz II second-degree AV block with wide QRS 1, 2, 5
• Third-degree (complete) heart block with wide QRS 1, 2, 5
• New bundle-branch block patterns 1, 2
• Heart transplant patients without autonomic reinnervation (may cause paradoxical high-degree AV block) 1

If the patient has infranodal block, skip atropine entirely and proceed directly to transcutaneous pacing or chronotropic infusions. 1, 2

Second-Line Treatments When Atropine Fails

Transcutaneous Pacing (TCP)

Do not delay TCP while giving multiple atropine doses. Apply pacing pads after the first or second atropine dose if heart rate remains inadequate. 1, 2, 3 TCP is a Class IIa recommendation for unstable patients unresponsive to atropine. 1, 2

Chronotropic Infusions (If TCP Unavailable or Ineffective)

Dopamine:

• Start at 5–10 mcg/kg/min IV infusion 1, 3
• Titrate every 2–5 minutes to hemodynamic response 1
• Maximum dose: 20 mcg/kg/min (higher doses cause excessive vasoconstriction and arrhythmias) 1

Epinephrine:

• Start at 2–10 mcg/min IV infusion 1, 3
• Preferred when severe hypotension requires combined chronotropic and inotropic support 1, 2

Special Clinical Scenarios

Acute Coronary Syndrome / Myocardial Infarction

• Use atropine cautiously—increasing heart rate may worsen ischemia or enlarge infarct size 1, 2
• Limit total atropine dose to 2–3 mg (lower than standard 3 mg maximum) in post-MI patients 2
• Target heart rate of approximately 60 bpm—avoid aggressive rate increases 2

Neurogenic Shock / Spinal Cord Injury

• Atropine often fails due to unopposed parasympathetic activity 1
• Consider aminophylline 6 mg/kg IV over 20–30 minutes or theophylline 100–200 mg slow IV as alternatives 1, 6, 7

Drug-Induced Bradycardia

• Immediately reduce or stop the offending agent (e.g., beta-blockers, calcium channel blockers, digoxin, remifentanil) 1
• For beta-blocker or calcium channel blocker toxicity, consider calcium and glucagon in addition to atropine 3

Common Pitfalls to Avoid

1. Do not give atropine for asymptomatic bradycardia—this is contraindicated and may worsen outcomes 1
2. Do not exceed 3 mg total atropine—higher doses cause central anticholinergic syndrome (confusion, agitation, hallucinations) without additional benefit 1, 2
3. Do not delay pacing in unstable patients while administering multiple atropine doses 1, 2
4. Do not use atropine in wide-complex heart block—it will not work and may precipitate ventricular standstill 1, 2, 5
5. Ensure IV access and cardiac monitoring are established before drug administration 1, 2

Monitoring During Treatment

• Continuous cardiac monitoring during and after atropine administration 1, 2
• Evaluate response by monitoring heart rate, blood pressure, and resolution of symptoms 1
• Be prepared to escalate to TCP or chronotropic infusions if condition deteriorates 1, 2