What is the management of bradycardia in ST-Elevation Myocardial Infarction (STEMI)?

Management of Bradycardia in STEMI

For symptomatic bradycardia in STEMI, intravenous atropine (0.6-1.0 mg) should be administered as first-line therapy, followed by temporary pacing if atropine fails to restore adequate heart rate and hemodynamic stability. 1

Assessment of Bradycardia in STEMI

Types of Bradycardia in STEMI

• Sinus bradycardia: Common in inferior MI due to increased vagal tone
• AV blocks: May occur with either inferior or anterior MI
  • Inferior MI: Usually supra-Hisian (nodal) blocks that often respond to atropine
  • Anterior MI: Usually infra-Hisian blocks with higher mortality due to extensive myocardial damage

Hemodynamic Assessment

• Symptomatic bradycardia requiring intervention includes:
  • Heart rate <40 bpm with hypotension (systolic BP <90 mmHg)
  • Signs of hemodynamic compromise
  • Chest pain
  • Shortness of breath
  • Altered mental status

Treatment Algorithm

Step 1: Atropine Administration

• Dosing: 0.6-1.0 mg IV bolus 1
• Maximum: Can repeat every 3-5 minutes up to total dose of 2 mg
• Mechanism: Blocks muscarinic acetylcholine receptors, increasing sinus node automaticity 2
• Caution: Atropine may worsen ischemia in some cases and has unpredictable effects in heart block at the His-Purkinje level (infranodal) 3

Step 2: If Inadequate Response to Atropine

• Apply transcutaneous pacing pads and initiate standby pacing 1
• Consider positive chronotropic medications if pacing not immediately available:
  • Epinephrine
  • Dopamine
  • Isoproterenol (use with caution in ischemic settings) 1

Step 3: Temporary Transvenous Pacing

• Indications: Persistent symptomatic bradycardia despite maximum atropine dosing 1
• Preferred approach: Atrial pacing when possible (for sinus node dysfunction)
• AV sequential pacing: Consider for patients with complete AV block, especially with RV infarction 1

Special Considerations

Location-Specific Management

• Inferior MI with bradycardia:

  • Often transient and responds well to atropine
  • Usually due to increased vagal tone or AV nodal ischemia
  • Generally has better prognosis 1, 4
  • Use caution with beta-blockers 5

• Anterior MI with bradycardia:

  • Often due to extensive myocardial damage
  • Higher mortality risk
  • May require earlier pacing intervention
  • More likely to need permanent pacing 1

Revascularization Considerations

• Urgent angiography with view to revascularization is indicated if the patient has not received previous reperfusion therapy 1
• Bradycardia may resolve after successful reperfusion, particularly in inferior MI 1

Potential Complications and Pitfalls

• Paradoxical response to atropine: In some cases of infranodal block, atropine can worsen bradycardia 3
• Excessive atropine dosing: Can lead to ventricular tachyarrhythmias, sustained sinus tachycardia, or delirium 4
• Periprocedural bradycardia during PCI: Associated with worse outcomes; risk factors include no-reflow phenomenon, LAD as culprit vessel, and use of thrombus aspiration devices 6

Indications for Permanent Pacing

• Temporary need for pacing during STEMI does not automatically indicate need for permanent pacing 1

• Consider permanent pacing for:

  • Persistent high-degree AV block
  • New bundle branch block with transient advanced AV block
  • Persistent symptomatic sinus node dysfunction

• When considering permanent pacing, evaluate patient for:

  • ICD indications (especially if reduced EF)
  • Biventricular pacing/cardiac resynchronization therapy 1

Remember that bradycardia management in STEMI requires careful monitoring and a stepwise approach, with treatment tailored to the location of infarction and hemodynamic status of the patient.