What is the management for 3rd degree (third degree) heart block?

Management of Third-Degree Heart Block

Permanent pacemaker implantation is the definitive treatment for third-degree heart block at any anatomic level, regardless of symptoms, when the condition is not expected to resolve. 1

Initial Assessment and Stabilization

• Assess hemodynamic stability immediately:

  • Check for symptoms of poor perfusion: altered mental status, chest pain, heart failure, hypotension, shock
  • Monitor vital signs including heart rate, blood pressure, respiratory rate, oxygen saturation
  • Obtain 12-lead ECG to confirm diagnosis and identify escape rhythm characteristics
  • Establish IV access

• For unstable patients with symptomatic bradycardia:

  1. Administer atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg) 2, 3

     • Note: Atropine may be ineffective in infranodal blocks (typically with wide QRS escape rhythm)
     • Doses <0.5 mg may paradoxically worsen bradycardia

  2. If unresponsive to atropine:

     • Initiate transcutaneous pacing immediately
     • Consider IV infusion of β-adrenergic agonists:
       • Dopamine (2-10 μg/kg/min) or
       • Epinephrine (2-10 μg/min) 2

  3. If transcutaneous pacing is ineffective or poorly tolerated:

     • Proceed to temporary transvenous pacing 2

Definitive Management

Class I Indications for Permanent Pacemaker Implantation:

1. Third-degree AV block at any anatomic level with any of the following:

   • Symptomatic bradycardia (including heart failure) 1
   • Ventricular arrhythmias presumed due to AV block 1
   • Conditions requiring medications that result in symptomatic bradycardia 1
   • Documented periods of asystole ≥3.0 seconds or escape rate <40 bpm in awake, symptom-free patients 1
   • Pauses ≥5 seconds in patients with atrial fibrillation 1
   • Asymptomatic persistent third-degree AV block with average awake ventricular rates ≥40 bpm if cardiomegaly or LV dysfunction is present 1
   • Asymptomatic persistent third-degree AV block if the site of block is below the AV node 1
   • Post-catheter ablation of the AV junction 1
   • Postoperative AV block not expected to resolve 1
   • Associated with neuromuscular diseases (with or without symptoms) 1

2. For specific patient populations:

   • Congenital third-degree AV block with:
     • Wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction 1
     • Ventricular rate <55 bpm in infants or <70 bpm with congenital heart disease 1

Special Considerations

• Reversible causes: Correct electrolyte abnormalities and discontinue medications that may cause AV block before proceeding to permanent pacing 1

• Potentially reversible but requiring pacing: Certain conditions may warrant pacemaker implantation even if AV block reverses transiently due to risk of disease progression:

  • Sarcoidosis
  • Amyloidosis
  • Neuromuscular diseases 1

• Lyme disease: May follow natural course to resolution; temporary pacing may be sufficient while treating the underlying infection 1, 4

• Post-MI setting: Permanent pacing is indicated for persistent second-degree AV block in the His-Purkinje system with bilateral BBB or complete heart block after acute MI 1

Pacing Mode Selection

• For patients with LVEF ≤35% who require significant (>40%) ventricular pacing, consider cardiac resynchronization therapy (CRT) 2
• For patients with LVEF 36-50% and high-degree or complete heart block, CRT is reasonable 2

Prognosis

Without permanent pacing, patients with third-degree heart block have poor long-term survival rates. Five-year survival rates are significantly better in paced versus unpaced patients (78% vs 41%) 5.

Common Pitfalls

• Failure to recognize third-degree AV block: Complete dissociation between P waves and QRS complexes may be mistaken for sinus bradycardia
• Inappropriate reliance on atropine: May be ineffective in infranodal blocks
• Delaying pacemaker implantation: Even asymptomatic patients with third-degree heart block typically require permanent pacing due to risk of sudden cardiac death
• Missing underlying causes: Always investigate for reversible causes (ischemia, medication effects, electrolyte abnormalities, infiltrative diseases)