What is the treatment for atrial tachycardia with second-degree Atrioventricular (AV) block?

Treatment for Atrial Tachycardia with Second-Degree AV Block

For patients with atrial tachycardia complicated by second-degree AV block, permanent pacemaker implantation is indicated, particularly when the block is infranodal (Mobitz type II), while simultaneously addressing the underlying tachyarrhythmia with appropriate antiarrhythmic therapy. 1

Initial Assessment and Management

Determine the Type and Location of AV Block

• Mobitz Type I (Wenckebach):

  • Usually occurs at the AV node level
  • Progressive PR prolongation before dropped beat
  • Generally narrow QRS complexes
  • Often benign and may not require permanent pacing

• Mobitz Type II:

  • Usually infranodal (His-Purkinje system)
  • Constant PR interval before dropped beat
  • Often wide QRS complexes
  • Higher risk of progression to complete heart block
  • Requires permanent pacing even if asymptomatic 1

Acute Management

1. Hemodynamically unstable patients:

   • Immediate synchronized cardioversion 1
   • Prepare for temporary pacing 2

2. Hemodynamically stable patients:

   • Atropine 0.5-1 mg IV (maximum 3 mg) for symptomatic bradycardia 2
   • Note: Atropine is often ineffective for infranodal (Mobitz type II) block 2
   • If atropine fails, consider epinephrine (2-10 μg/min) or dopamine (2-10 μg/kg/min) infusion 2

3. Temporary pacing measures:

   • Transcutaneous pacing for unstable patients not responding to medications 2
   • Transvenous temporary pacing for patients refractory to medical therapy 2

Definitive Management

Permanent Pacemaker Indications

• Class I indications (strongly recommended):

  • Second-degree AV block with symptomatic bradycardia regardless of type or site of block 1
  • Third-degree and advanced second-degree AV block at any anatomic level associated with bradycardia and symptoms 1
  • Type II second-degree AV block (even if asymptomatic) 1

• Class IIa indications (reasonable):

  • Asymptomatic persistent third-degree AV block with adequate escape rhythm 1

Management of Atrial Tachycardia

After addressing the AV block with pacing, treat the atrial tachycardia with:

1. Pharmacological options:

   • Beta-blockers (use with caution if AV block persists) 3
   • Consider catheter ablation for recurrent, symptomatic atrial tachycardia 4

2. Avoid medications that can worsen AV block:

   • Flecainide (can cause sinus bradycardia, sinus arrest, or worsen AV block) 5
   • Diltiazem and verapamil (can exacerbate AV block) 6
   • Digoxin (can worsen AV block) 1

Special Considerations

Reversible Causes

• Always evaluate for potentially reversible causes of AV block:
  • Electrolyte abnormalities
  • Medication effects (beta-blockers, calcium channel blockers)
  • Lyme disease
  • Enhanced vagal tone
  • Perioperative hypothermia 1

Caution with Medications

• Even if pacemaker is implanted, use caution with medications that affect cardiac conduction:
  • Flecainide increases PR, QRS, and QT intervals by approximately 25% 5
  • Diltiazem can cause bradycardia and high-degree AV block 6

Prognosis

• AV block during tachyarrhythmias is not always benign and may indicate underlying conduction system disease 7
• Studies show that AV block that occurs during medication use often recurs after drug discontinuation, suggesting underlying conduction disease rather than pure drug effect 8

Follow-up

• Regular evaluation of pacemaker function
• Monitoring for progression of conduction disease
• Adjustment of antiarrhythmic therapy as needed

Pitfalls to Avoid

• Assuming AV block during tachycardia is always functional and benign 7
• Delaying pacemaker implantation in patients with Mobitz type II block, even if asymptomatic 1
• Using medications that can worsen AV block (calcium channel blockers, beta-blockers) without appropriate pacing backup 6
• Attributing AV block solely to medications when underlying conduction disease may be present 8