What is the immediate management for a patient with second degree atrioventricular (AV) block?

Immediate Management of Second-Degree AV Block

For patients with second-degree AV block, immediate management should include atropine administration for symptomatic bradycardia, followed by transcutaneous pacing if unresponsive to medication, and urgent evaluation for permanent pacing, particularly for Mobitz type II block. 1, 2

Initial Assessment and Classification

The management approach depends on:

1. Type of second-degree AV block:

   • Mobitz type I (Wenckebach): Progressive PR prolongation before dropped QRS; usually AV nodal
   • Mobitz type II: Constant PR intervals with sudden dropped QRS; usually infranodal (His-Purkinje system)
   • 2:1 AV block: Cannot be classified as type I or II but location can be inferred 3, 4

2. Hemodynamic stability:

   • Presence of hypotension, signs of poor perfusion, altered mental status
   • Associated symptoms (syncope, presyncope, dizziness)

3. QRS complex width:

   • Narrow QRS suggests AV nodal block (generally better prognosis)
   • Wide QRS suggests infranodal block (higher risk of progression to complete heart block) 5, 3

Immediate Management Algorithm

Step 1: Assess and Stabilize

• Ensure patent airway, administer oxygen if hypoxemic
• Establish IV access
• Continuous cardiac monitoring and 12-lead ECG
• Assess vital signs and perfusion status 2

Step 2: Pharmacological Therapy for Symptomatic Bradycardia

• Atropine 0.5-1.0 mg IV (can repeat every 3-5 minutes to maximum 3 mg total)
  • Particularly effective for Mobitz type I (nodal block)
  • Less effective for Mobitz type II (infranodal block)
  • Caution: doses <0.5 mg may paradoxically worsen bradycardia 2, 6

Step 3: If Unresponsive to Atropine

• Initiate transcutaneous pacing for hemodynamically unstable patients
  • Apply pads anteriorly and posteriorly
  • Start at 50-60 bpm, increase as needed for hemodynamic stability
  • Use sedation as needed for patient comfort 1, 2

Step 4: Prepare for Transvenous Pacing

• For patients with persistent symptomatic bradycardia despite medical therapy
• Particularly important for Mobitz type II block due to high risk of progression to complete heart block 1, 2

Specific Management Based on Block Type

For Mobitz Type I (Wenckebach)

• Often transient and hemodynamically stable
• If asymptomatic with normal hemodynamics: observation may be sufficient
• If symptomatic: atropine first, temporary pacing if needed 1

For Mobitz Type II

• Higher risk of progression to complete heart block
• Requires immediate preparation for temporary pacing even if currently stable
• Consider urgent transvenous pacing if transcutaneous pacing is inadequate
• Evaluate for permanent pacemaker placement 1, 4

For 2:1 AV Block

• Management depends on QRS width and clinical context
• Wide QRS suggests infranodal block: treat like Mobitz type II
• Narrow QRS in appropriate clinical context (e.g., inferior MI): may respond to atropine 3

Special Considerations

• In acute MI setting: Revascularization should be considered for patients with AV block who have not yet received reperfusion therapy 1
• Bundle branch blocks: New-onset bundle branch block with second-degree AV block suggests extensive myocardial damage and higher risk of progression 1
• Reversible causes: Always identify and treat potential reversible causes (medications, electrolyte abnormalities, increased vagal tone) 2
• Pseudo-AV block: Consider concealed His bundle or ventricular extrasystoles that may mimic second-degree AV block 7

Indications for Permanent Pacing

• Persistent second-degree AV block in the His-Purkinje system with bilateral bundle branch block
• Transient advanced second-degree AV block with associated bundle branch block
• Persistent and symptomatic second- or third-degree AV block
• Mobitz type II second-degree AV block (even if asymptomatic) 1

Remember that Mobitz type II block is invariably infranodal and carries a high risk of progression to complete heart block, making it a clear indication for pacemaker therapy regardless of symptoms 4.