What are the management options for heart block?

Management of Heart Block

The management of heart block depends on the type, location, and hemodynamic consequences of the block, with permanent pacemaker implantation indicated for persistent second-degree AV block in the His-Purkinje system, third-degree AV block, or symptomatic bradycardia. 1

Classification and Initial Assessment

Heart block is categorized by severity:

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

Immediate Assessment

• Evaluate for signs of hemodynamic compromise: altered mental status, hypotension, chest pain, heart failure, shortness of breath, syncope 1
• Identify potential reversible causes: ischemia, electrolyte abnormalities, medication effects, infection 2
• Determine location of block (nodal vs. infranodal) as this affects treatment approach 3

Acute Management

Symptomatic Bradycardia or Hemodynamic Compromise

1. Medical Therapy:

   • Atropine: 0.5-1.0 mg IV (up to maximum 3 mg) for symptomatic bradycardia, especially effective for AV nodal block 4, 1
   • Beta-adrenergic agonists: Consider isoproterenol, dopamine (2-10 μg/kg/min), or epinephrine (2-10 μg/min) if atropine ineffective 3
   • Aminophylline: May be considered for AV block in setting of inferior MI 3

2. Temporary Pacing:

   • Transcutaneous pacing: For immediate management when medical therapy fails 3
   • Transvenous pacing: For persistent symptomatic bradycardia refractory to medical therapy 3
   • Consider externalized permanent active fixation lead over standard temporary pacing lead for prolonged temporary pacing 3

Management Based on Location of Block

• AV Nodal Block (often in inferior MI):

  • More likely to respond to atropine
  • Often transient and may not require permanent pacing 3, 5

• Infranodal Block (often in anterior MI):

  • Associated with extensive myocardial damage
  • Higher mortality risk
  • Less responsive to atropine
  • More likely to require permanent pacing 3, 1

Indications for Permanent Pacemaker

Class I Indications (Strong Recommendation) 3, 1:

• Persistent second-degree AV block in the His-Purkinje system with bilateral bundle branch block
• Third-degree AV block within or below the His-Purkinje system
• Transient advanced second- or third-degree infranodal 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)

Class IIb Indications (May Be Considered) 3:

• Persistent second- or third-degree AV block at the AV node level

Not Recommended for Permanent Pacing 3:

• Transient AV block without intraventricular conduction defects
• Transient AV block with isolated left anterior fascicular block
• Acquired left anterior fascicular block without AV block
• Persistent first-degree AV block with bundle branch block of old or indeterminate age

Special Considerations

• Bundle Branch Block with MI: Patients with new bundle branch block (especially RBBB with left fascicular block) during MI are at high risk of progression to high-degree AV block and should receive prophylactic temporary pacing 6

• First-degree AV Block: Generally benign, but extreme prolongation (PR >0.30 sec) may cause symptoms similar to pacemaker syndrome and may warrant consideration of pacing 7

• Medication Management: Identify and discontinue medications that worsen AV conduction (beta-blockers, calcium channel blockers, digitalis) 1

• Electrolyte Disturbances: Correct before considering permanent pacemaker therapy 1

• Cardiac Resynchronization Therapy (CRT): Consider for patients with LVEF ≤35% who require significant ventricular pacing 1

Follow-up Care

• Regular monitoring for patients with conditions that may progress to complete heart block
• All patients receiving permanent pacemakers should be evaluated for ICD indications 3
• Consider dual-chamber pacing for patients in sinus rhythm and single-chamber ventricular pacing for those in permanent atrial fibrillation 3

By following this structured approach to heart block management, clinicians can provide appropriate acute interventions and determine the need for permanent pacing based on the type, location, and hemodynamic consequences of the block.