What is the management of heart block?

Management of Heart Block

Heart block management depends on the type, location, and hemodynamic consequences, with temporary pacing indicated for symptomatic bradycardia unresponsive to atropine and permanent pacing for persistent high-grade AV blocks. 1

Types of Heart Block and Initial Assessment

Heart block refers to delayed or interrupted conduction between the atria and ventricles, classified as:

• First-degree AV block: Prolonged PR interval (>0.20 seconds)

  • Generally requires no treatment 1
  • May not be entirely benign in all cases, as some patients progress to higher-grade blocks 2

• Second-degree AV block:

  • Type I (Mobitz I/Wenckebach): Progressive PR prolongation before dropped beat

    • Usually associated with inferior infarction
    • Treatment only if symptomatic or causing hemodynamic compromise 1

  • Type II (Mobitz II): Sudden dropped beats without PR prolongation

    • Indication for pacemaker insertion 1

• Third-degree (Complete) AV block: No atrial impulses conducted to ventricles

  • Requires pacing if symptomatic or hemodynamically unstable 1

Acute Management Algorithm

1. Hemodynamically Unstable Patients:

• Immediate intervention required:

  • IV atropine 0.5-1.0 mg (can repeat up to total 3 mg) for symptomatic bradycardia 1, 3
  • Avoid atropine doses <0.5 mg which may paradoxically worsen bradycardia 1
  • For infranodal blocks (Type II second-degree or third-degree with wide QRS), atropine is ineffective 1

• If no response to atropine:

  • Initiate temporary transcutaneous pacing 1
  • Proceed to transvenous temporary pacing if transcutaneous pacing ineffective 1

2. Specific Management Based on Block Type:

For First-degree AV Block:

• No specific treatment required unless PR interval >0.30s with symptoms 4
• Monitor for progression to higher-grade block 2

For Second-degree Type I (Mobitz I):

• If asymptomatic: observation only
• If symptomatic: atropine first, then pacing if needed 1

For Second-degree Type II (Mobitz II):

• Temporary pacing electrode insertion recommended 1
• Proceed to permanent pacing if persistent 1

For Complete (Third-degree) AV Block:

• Temporary pacing required for symptomatic patients 1
• Permanent pacing for persistent complete heart block 1
• Urgent angiography with revascularization if associated with acute MI 1

Special Considerations

Heart Block in Myocardial Infarction:

• Inferior MI: Often involves AV node (usually transient)

  • Sinus bradycardia common in first hour 1
  • First-degree or Mobitz I block usually resolves with reperfusion 1
  • Atropine effective for symptomatic bradycardia 1

• Anterior MI: Often involves infra-Hisian system (more serious)

  • New bundle branch block or bifascicular block suggests extensive infarction 1
  • Higher risk of progression to complete heart block 1
  • Preventive temporary pacing may be warranted 1

Heart Block in Myocarditis:

• Temporary pacemaker insertion recommended for symptomatic heart block 1
• Permanent pacing for persistent AV blocks 1
• Device selection should consider LV dysfunction prognosis 1

Indications for Permanent Pacing

Permanent pacemaker implantation is indicated for:

1. Persistent second-degree AV block in the His-Purkinje system with bilateral BBB 1
2. Transient advanced AV block with associated BBB 1
3. Symptomatic AV block at any level 1
4. Complete AV block with hemodynamic compromise 1

Pitfalls and Caveats

• Do not delay temporary pacing in symptomatic high-grade AV block unresponsive to atropine
• Always rule out reversible causes before permanent pacemaker implantation:
  • Medication effects (beta-blockers, calcium channel blockers)
  • Electrolyte abnormalities
  • Acute ischemia
  • Infectious diseases 5
• Avoid prophylactic antiarrhythmic drugs as they may be harmful 1
• Recognize that first-degree AV block is not always benign and may warrant monitoring for progression 2
• Consider the location of block when choosing therapy - infranodal blocks respond poorly to atropine 1

Heart block management requires prompt recognition, appropriate monitoring, and timely intervention based on the type of block and hemodynamic status to prevent adverse outcomes including sudden cardiac death.