What are the management options for heart block?

Management of Heart Block

Permanent pacing is recommended for patients with acquired second-degree Mobitz type II atrioventricular block, high-grade atrioventricular block, or third-degree atrioventricular block not attributable to reversible causes, regardless of symptoms. 1

Classification and Initial Assessment

Heart block is categorized by severity and location:

• First-degree AV block: PR interval >200 ms

  • Generally benign and requires no specific treatment
  • Exception: Marked first-degree AV block (PR >240 ms) with symptoms attributable to AV dyssynchrony 1

• 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

• High-grade AV block: Multiple consecutive non-conducted P waves

Acute Management Algorithm

1. Assess Hemodynamic Stability

• If unstable (hypotension, altered mental status, chest pain, dyspnea):
  • Begin with atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg) 2, 3
  • Note: Atropine may be ineffective in Mobitz type II and third-degree AV block with wide QRS 2
  • Caution: Atropine may paradoxically worsen bradycardia in doses <0.5 mg 2

2. If Unresponsive to Atropine

• Initiate transcutaneous pacing while preparing for transvenous pacing 2
• Consider IV infusion of β-adrenergic agonists:
  • Dopamine (2-10 μg/kg/min) or epinephrine (2-10 μg/min) 2

3. For Persistent Symptoms or Hemodynamic Compromise

• Temporary transvenous pacing is reasonable 1
• For prolonged temporary pacing, consider externalized permanent active fixation lead 1

4. Identify and Treat Reversible Causes

• Medication effects (beta-blockers, calcium channel blockers, digoxin)
• Electrolyte abnormalities
• Acute myocardial ischemia/infarction
• Infectious diseases (Lyme, endocarditis)
• Vagal stimulation 4

Indications for Permanent Pacemaker

Class I Recommendations (Strong)

1. Acquired second-degree Mobitz type II AV block, high-grade AV block, or third-degree AV block not attributable to reversible causes, regardless of symptoms 1

2. Neuromuscular diseases with evidence of second-degree AV block, third-degree AV block, or HV interval ≥70 ms, regardless of symptoms 1

3. Permanent atrial fibrillation with symptomatic bradycardia 1

4. Symptomatic AV block due to necessary medications without alternative treatment options 1

5. Symptomatic AV block attributable to a known reversible cause that does not resolve despite treatment 1

Class IIa Recommendations (Reasonable)

1. Infiltrative cardiomyopathy (cardiac sarcoidosis, amyloidosis) with second-degree Mobitz type II, high-grade, or third-degree AV block 1

2. Lamin A/C gene mutations with PR interval >240 ms and LBBB 1

3. Marked first-degree or second-degree Mobitz type I AV block with symptoms clearly attributable to the AV block 1

Class III Recommendations (Not Recommended)

1. Acute AV block attributable to a known reversible and non-recurrent cause that has resolved 1

2. Asymptomatic vagally mediated AV block 1

Special Considerations

Myocardial Infarction Context

• In inferior MI: AV block often transient and may respond to atropine 1
• In anterior MI with new bundle branch block or hemiblock: High likelihood of developing complete AV block; preventive temporary pacing may be warranted 1
• Consider aminophylline for AV block in acute inferior MI 1

Heart Failure Patients

• For patients with LVEF ≤35% who require significant (>40%) ventricular pacing, cardiac resynchronization therapy (CRT) should be considered 1
• In patients with high-degree or complete heart block and LVEF 36-50%, CRT is reasonable 1

Additional Testing for Management

• Ambulatory ECG monitoring: Reasonable for patients with symptoms of unclear etiology who have first-degree or second-degree Mobitz type I AV block 1

• Exercise testing: Consider for patients with exertional symptoms who have first-degree or second-degree Mobitz type I AV block at rest 1

• Electrophysiology study: May be considered in selected patients with second-degree AV block to determine the level of block 1

Key Pitfalls to Avoid

1. Failing to identify potentially reversible causes before permanent pacemaker implantation

2. Delaying pacing in hemodynamically unstable patients with high-grade AV block unresponsive to atropine

3. Relying on atropine for Mobitz type II or infranodal complete heart block, where it's often ineffective

4. Overlooking the need for CRT in heart failure patients requiring significant ventricular pacing

5. Implanting permanent pacemakers for transient AV block that has completely resolved (e.g., drug-induced, vagally mediated) 1