What is the management approach for a patient with symptomatic 2nd degree Atrioventricular (AV) block, specifically Mobitz II?

Management of Symptomatic 2nd Degree AV Block Mobitz II

Permanent pacemaker implantation is recommended for patients with symptomatic second-degree Mobitz type II atrioventricular block regardless of other factors. 1

Pathophysiology and Clinical Significance

Mobitz type II second-degree AV block is characterized by:

• Intermittent non-conducted P waves without progressive PR interval prolongation
• Usually infranodal in location (below the AV node)
• Often associated with wide QRS complexes
• High risk of progression to complete heart block
• Typically indicates significant conduction system disease 1

Unlike Mobitz type I (Wenckebach), which is usually benign and occurs at the level of the AV node, Mobitz type II is considered more dangerous and requires definitive intervention.

Immediate Management

For symptomatic patients presenting with Mobitz II AV block:

1. Stabilize the patient:

   • If hemodynamically unstable: Administer atropine 0.5 mg IV (may repeat to maximum 2.0 mg) 2
   • Consider temporary pacing if patient is unstable and unresponsive to atropine
   • Monitor vital signs and cardiac rhythm continuously

2. Exclude reversible causes:

   • Medication effects (beta-blockers, calcium channel blockers, digoxin)
   • Electrolyte abnormalities
   • Acute myocardial ischemia/infarction
   • Infectious/inflammatory conditions

Definitive Management

Permanent pacemaker implantation is the definitive treatment for symptomatic Mobitz II AV block. This is a Class I recommendation (highest level) from the ACC/AHA/HRS guidelines 1.

Key considerations for pacemaker implantation:

• Timing: Implantation should occur before discharge if the block is not expected to resolve 1
• Device selection: Dual-chamber pacing (DDD) is typically preferred to maintain AV synchrony
• Programming: Should aim to maintain native AV conduction when possible 1

Special Considerations

1. Patients with structural heart disease:

   • Consider additional defibrillator capability if the patient has risk factors for sudden cardiac death 1
   • For patients with hypertrophic cardiomyopathy who develop Mobitz II AV block after septal ablation or myectomy, permanent pacing is recommended before discharge 1

2. Patients with neuromuscular diseases:

   • Patients with neuromuscular diseases associated with conduction disorders who develop Mobitz II AV block should receive permanent pacing, with additional defibrillator capability if needed 1

3. Post-procedural AV block:

   • For new Mobitz II AV block after cardiac procedures (e.g., TAVR) associated with symptoms or hemodynamic instability that does not resolve, permanent pacing is recommended before discharge 1

Follow-up Care

After pacemaker implantation:

• Device interrogation within 2-12 weeks of implantation
• Regular device checks (typically every 3-12 months)
• Monitor for complications including lead dislodgement, infection, and pacemaker syndrome

Prognosis

Without intervention, Mobitz type II AV block has a high risk of progression to complete heart block, which can lead to Stokes-Adams attacks, syncope, and sudden cardiac death 3. Even asymptomatic patients with Mobitz II block have been shown to benefit from prophylactic pacing due to the high risk of progression 4.

With appropriate pacemaker therapy, prognosis is generally good, though underlying cardiac disease may influence long-term outcomes.

Conclusion

Symptomatic Mobitz II AV block represents a clear indication for permanent pacemaker implantation. The evidence strongly supports this approach to prevent progression to complete heart block and associated morbidity and mortality.