ACLS Algorithm for Bradycardia
For symptomatic bradycardia causing hemodynamic instability, immediately administer atropine 0.5-1 mg IV as first-line treatment, repeating every 3-5 minutes up to a maximum of 3 mg, followed by transcutaneous pacing and/or chronotropic infusions (dopamine 5-10 mcg/kg/min or epinephrine 2-10 mcg/min) if atropine fails. 1, 2
Initial Assessment
Determine if the bradycardia is causing symptoms or hemodynamic compromise by evaluating for: 1
- Altered mental status
- Ischemic chest discomfort
- Acute heart failure
- Hypotension (systolic BP <80 mmHg)
- Other signs of shock
Simultaneously: 1
- Maintain patent airway and assist breathing as necessary
- Provide supplemental oxygen if hypoxemic or increased work of breathing
- Establish cardiac monitoring and IV access
- Obtain 12-lead ECG to identify rhythm and conduction abnormalities
- Identify and treat reversible causes (hypoxemia, electrolytes, medications, ischemia)
Treatment Algorithm
Step 1: First-Line Pharmacologic Treatment
Atropine 0.5-1 mg IV bolus 1, 2, 3
- Repeat every 3-5 minutes as needed
- Maximum total dose: 3 mg
- Critical warning: Doses <0.5 mg may paradoxically slow heart rate further—avoid 1
Atropine is likely effective for: 1, 2
- Sinus bradycardia
- AV nodal block (first-degree or Mobitz I second-degree)
- Sinus arrest
Atropine is likely ineffective for: 1, 2
- Mobitz II second-degree AV block
- Third-degree AV block with wide QRS complex (infranodal block)
- Post-cardiac transplant patients (may cause paradoxical high-degree AV block)
Step 2: Second-Line Treatment (If Atropine Fails)
Transcutaneous Pacing (TCP) 1, 2
- Initiate immediately in unstable patients not responding to atropine (Class IIa recommendation)
- Apply pacing pads early in high-risk patients (Mobitz II, third-degree block)
- Requires sedation/analgesia in conscious patients
- Serves as bridge to transvenous pacing if needed
AND/OR Chronotropic Infusions:
Dopamine 5-10 mcg/kg/min IV infusion 1
- Start at 5 mcg/kg/min, titrate by 2-5 mcg/kg/min every 2-5 minutes
- Provides both chronotropic and inotropic effects at this dose range
- Do not exceed 20 mcg/kg/min (causes excessive vasoconstriction and arrhythmias)
- Preferred when inotropic support is also needed
Epinephrine 2-10 mcg/min IV infusion 1
- Alternative to dopamine
- Stronger alpha-adrenergic effects with more vasoconstriction
- Preferred in severe hypotension requiring urgent chronotropic/inotropic support
- Preferred agent in cardiac transplant patients (atropine contraindicated)
Isoproterenol 1-20 mcg/min IV infusion 1
- Provides chronotropy and inotropy without vasopressor effects
- May be preferable when pure rate acceleration is needed without vasoconstriction
Special Clinical Scenarios
Acute Coronary Syndrome/MI
Use all rate-accelerating drugs with extreme caution—increasing heart rate may worsen ischemia or increase infarct size. 1, 2
Heart Transplant Patients
- Avoid atropine (may cause paradoxical high-degree AV block due to lack of vagal innervation) 1
- Use epinephrine as first-line agent
Asymptomatic Bradycardia
No treatment indicated. 4
- Common in athletes, during sleep, or with elevated parasympathetic tone
- Heart rates <40 bpm can be physiologic
- Monitor and identify reversible causes only
Critical Pitfalls to Avoid
- Do not delay TCP while giving additional atropine doses in unstable patients 1, 2
- Do not use atropine doses <0.5 mg (paradoxical slowing) 1
- Do not exceed atropine 3 mg total (risk of central anticholinergic syndrome with confusion, agitation, hallucinations) 1
- Do not use atropine in post-transplant hearts or high-degree infranodal blocks 1, 2
- Do not exceed dopamine 20 mcg/kg/min (arrhythmias and excessive vasoconstriction) 1
Monitoring During Treatment
- Heart rate response
- Blood pressure
- Resolution of symptoms (mental status, chest pain, perfusion)
- Cardiac rhythm on monitor
- Prepare to escalate therapy if deterioration occurs