What is the initial management for a patient presenting with atrioventricular (AV) block?

Initial Management of Atrioventricular (AV) Block

The initial management of atrioventricular block should focus on assessing hemodynamic stability and determining the type and location of the block, with atropine as first-line therapy for symptomatic bradycardia caused by AV nodal blocks. 1

Assessment and Classification

First, determine the type of AV block:

• First-degree AV block: Prolonged PR interval (>0.20 seconds)
• Second-degree AV block:
  • Mobitz Type I (Wenckebach): Progressive PR prolongation until a beat is dropped
  • Mobitz Type II: Sudden dropped beats without PR prolongation
• Third-degree (complete) AV block: Complete dissociation between atria and ventricles

Next, determine the anatomical location of the block:

• AV nodal block: Usually narrow QRS complex, often associated with:

  • First-degree AV block
  • Mobitz Type I second-degree block
  • Inferior wall myocardial infarction

• Infranodal block (His-Purkinje system): Often wide QRS complex, associated with:

  • Mobitz Type II second-degree block
  • Third-degree block with wide QRS
  • Anterior wall myocardial infarction

Immediate Management Algorithm

1. Assess hemodynamic stability:

   • Check for hypotension, altered mental status, chest pain, shortness of breath, or signs of shock
   • Establish cardiac monitoring and obtain 12-lead ECG
   • Secure IV access

2. For hemodynamically stable patients:

   • Observe if asymptomatic first-degree AV block or Mobitz Type I without symptoms 2
   • Monitor for progression to higher-degree blocks

3. For symptomatic patients with AV nodal block (Mobitz Type I or nodal third-degree block):

   • Administer atropine 0.5 mg IV 2, 1
   • May repeat every 3-5 minutes to a maximum total dose of 3 mg
   • Avoid doses <0.5 mg as they may paradoxically worsen bradycardia 2, 3

4. For patients with infranodal block (Mobitz Type II or infranodal third-degree block):

   • Do NOT administer atropine as it may worsen the block 2, 1
   • Prepare for temporary pacing
   • Consider transcutaneous pacing if hemodynamically unstable

5. For patients unresponsive to atropine or with infranodal block:

   • Initiate transcutaneous pacing for immediate support
   • Arrange for transvenous temporary pacemaker insertion
   • Consider vasopressor support (dopamine 2-10 μg/kg/min or epinephrine 2-10 μg/min) 1

Special Considerations

• Medication review: Identify and discontinue medications that may cause or worsen AV block:

  • Beta-blockers
  • Calcium channel blockers (especially non-dihydropyridines like verapamil and diltiazem)
  • Digoxin
  • Antiarrhythmics

• Correct electrolyte abnormalities, particularly potassium and magnesium imbalances 1

• For AV block in acute myocardial infarction:

  • Inferior MI with AV block: Often transient, nodal, and responsive to atropine 2, 4
  • Anterior MI with AV block: Often infranodal, associated with extensive damage, and may require immediate pacing 5

Indications for Permanent Pacing

Consider permanent pacemaker implantation for:

• Symptomatic second-degree AV block of any type
• Asymptomatic Mobitz Type II second-degree AV block
• Third-degree AV block with symptoms
• Persistent second-degree AV block in the His-Purkinje system with bilateral bundle branch block 1

Common Pitfalls to Avoid

1. Misclassifying the type of AV block: Incorrectly identifying Mobitz Type I vs Type II can lead to inappropriate treatment decisions.

2. Using atropine for infranodal blocks: Atropine is ineffective and potentially harmful in Mobitz Type II and infranodal third-degree blocks 2, 1.

3. Delaying pacing in unstable patients: Patients with symptomatic bradycardia unresponsive to atropine require immediate temporary pacing.

4. Overlooking reversible causes: Always check for medication effects, electrolyte abnormalities, and acute ischemia before committing to permanent pacing.

5. Underestimating first-degree AV block: While often benign, severe first-degree AV block (PR >0.30 seconds) can cause symptoms similar to pacemaker syndrome and may require intervention 6.