What is the management for Atrioventricular (AV) block?

Management of Atrioventricular (AV) Block

Permanent pacemaker implantation is the definitive treatment for symptomatic third-degree AV block and Mobitz type II second-degree AV block, even in asymptomatic patients. 1

Classification of AV Block

AV block is classified into three degrees based on severity:

1. First-degree AV block:

   • Abnormally prolonged PR interval (>0.20 seconds)
   • All atrial impulses conduct to ventricles
   • Usually benign but may progress to higher-degree block

2. Second-degree AV block:

   • Mobitz type I (Wenckebach): Progressive PR prolongation until a beat is dropped

     • Usually occurs at AV node level
     • Generally benign with narrow QRS complex

   • Mobitz type II: Constant PR interval with sudden non-conducted P waves

     • Usually infranodal (below AV node)
     • Associated with wide QRS complex
     • Higher risk of progression to complete heart block

3. Third-degree (complete) AV block:

   • Complete absence of AV conduction
   • Atria and ventricles beat independently
   • May occur at any anatomic level

Management Algorithm

1. First-Degree AV Block

• Generally requires no specific treatment
• Monitor for progression to higher-degree block
• Consider pacemaker if:
  • PR interval >0.30 seconds with symptoms similar to pacemaker syndrome
  • Hemodynamic compromise is present 1, 2

2. Second-Degree AV Block

• Mobitz Type I (Wenckebach):

  • Usually benign and often requires no treatment
  • If symptomatic with bradycardia:
    • Atropine may be used acutely (0.5-1.0 mg IV) 3
    • Consider pacemaker if persistent symptoms

• Mobitz Type II:

  • Permanent pacemaker indicated even if asymptomatic 1, 4
  • AVOID beta-blockers and other AV nodal blocking agents as they may precipitate complete heart block 4
  • For acute management before pacemaker placement:
    • IV atropine for symptomatic bradycardia
    • Temporary pacing if no response to atropine 1

3. Third-Degree (Complete) AV Block

• Permanent pacemaker indicated for all symptomatic patients 1
• Permanent pacemaker recommended for asymptomatic patients (Class IIa indication) 1
• Acute management before pacemaker placement:
  • IV atropine for symptomatic bradycardia (0.5-1.0 mg)
  • If no response, use IV positive chronotropic medications (epinephrine, vasopressin)
  • Temporary pacing if medications fail 1

Special Considerations

AV Block in Acute Myocardial Infarction

• Inferior MI: AV block is usually supra-Hisian, transient, and often resolves with reperfusion

  • IV atropine for symptomatic bradycardia
  • Temporary pacing if atropine fails

• Anterior MI: AV block is usually infra-Hisian with extensive myocardial damage

  • Higher mortality risk
  • Consider early temporary pacing
  • Permanent pacemaker may be needed 1

AV Block with Bundle Branch Block

• New bundle branch block with AV block suggests extensive anterior MI
• Bifascicular or trifascicular block with syncope warrants electrophysiological study
• Prophylactic pacing indicated if infrahisal second-degree AV block is induced during electrophysiological testing 1, 5

Medications to Avoid in AV Block

• Use with caution or avoid in higher-degree blocks:
  • Beta-blockers
  • Non-dihydropyridine calcium channel blockers (diltiazem, verapamil)
  • Digoxin
  • Amiodarone 1, 4

Prognosis

• First-degree AV block: Recent evidence suggests it may not be entirely benign; 40.5% of patients with first-degree AV block in one study progressed to higher-grade block requiring pacemaker 6
• Mobitz type II: High risk of progression to complete heart block
• Complete AV block: Observational studies suggest permanent pacing improves survival, especially if syncope has occurred 1

Key Pitfalls to Avoid

1. Mistaking Mobitz type I for Mobitz type II (different prognosis and management)
2. Using beta-blockers in Mobitz type II block (can precipitate complete heart block)
3. Delaying pacemaker implantation in symptomatic complete AV block
4. Assuming all first-degree AV blocks are benign (may progress to higher-grade block)
5. Failing to recognize AV block associated with anterior MI as a high-risk condition

Remember that the management approach should be guided by the type of AV block, presence of symptoms, and underlying cardiac conditions, with permanent pacing being the definitive treatment for high-grade AV blocks.