What is the management of symptomatic Mobitz I (First-degree) Atrioventricular (AV) block?

Management of Symptomatic Mobitz I AV Block

For patients with symptomatic Mobitz I (Wenckebach) AV block, atropine should be administered as first-line therapy, followed by temporary pacing if symptoms persist, with permanent pacemaker implantation indicated for persistent symptomatic cases despite medical management.

Initial Assessment and Management

Pharmacological Therapy

• First-line treatment: Atropine 0.5 mg IV every 3-5 minutes (maximum total dose of 3 mg) 1

  • Atropine is most effective for AV block at the nodal level (which is where Mobitz I typically occurs) 2, 1
  • Caution: Doses less than 0.5 mg may paradoxically worsen bradycardia 2, 1

• Second-line treatment (if unresponsive to atropine):

  • IV infusion of β-adrenergic agonists:
    • Dopamine (2-10 μg/kg/min IV infusion) or
    • Epinephrine (2-10 μg/min IV infusion) 1

Temporary Pacing

• Transcutaneous pacing should be considered for patients with:

  • Symptomatic bradycardia unresponsive to atropine 2
  • Hemodynamic compromise refractory to antibradycardic medical therapy 2

• Temporary transvenous pacing may be necessary if:

  • Transcutaneous pacing is ineffective or not tolerated
  • Prolonged temporary pacing is anticipated 2

Diagnostic Evaluation

For patients with symptomatic Mobitz I AV block, additional testing is recommended to determine the need for permanent pacing:

• Ambulatory electrocardiographic monitoring is reasonable to establish correlation between symptoms and rhythm abnormalities 2

• Exercise treadmill test is reasonable for patients with exertional symptoms (e.g., chest pain, shortness of breath) to determine whether they may benefit from permanent pacing 2

• Electrophysiological study (EPS) may be considered in selected patients to determine the level of the block (nodal vs. infranodal) 2, 3

  • Infranodal Mobitz I is rare but carries a higher risk of progression to complete heart block 3

Indications for Permanent Pacemaker Implantation

Class I Indications (Strongly Recommended):

• Symptomatic Mobitz I AV block that does not resolve despite treatment of any underlying reversible cause 2
• Mobitz I AV block with symptoms clearly attributable to the AV block 1

Important Considerations:

• Mobitz I block is not benign in patients ≥45 years of age, and pacemaker implantation should be considered even in the absence of symptomatic bradycardia 4
• Paced patients have better long-term survival than unpaced patients (5-year survival 76.3% vs 53.5%) 4, 5
• In a study of older patients with Mobitz I AV block, cardiac implantable electronic device placement was associated with a 46% reduction in mortality 5

Special Considerations

Medication Management

• Avoid medications that can worsen AV block:

  • Beta-blockers
  • Non-dihydropyridine calcium channel blockers
  • Digoxin
  • Tricyclic antidepressants 1, 6

• Drug-induced AV block:

  • Discontinuation of culprit drugs leads to resolution in approximately 72% of cases 6
  • However, 27% of patients may experience recurrence of AV block despite discontinuation 6
  • Approximately half of patients with drug-induced AV block ultimately require permanent pacemaker implantation 6

Monitoring

• Continuous cardiac monitoring during initial treatment
• Serial ECGs to assess response to therapy
• Regular evaluation for progression of conduction disease 1

Pitfalls and Caveats

• Mobitz I AV block is traditionally considered benign, but recent evidence suggests otherwise, particularly in older patients 4, 5
• Distinguishing nodal from infranodal Mobitz I is critical as infranodal block has worse prognosis and higher likelihood of progression to complete heart block 3
• Drug-induced AV block should not be assumed to be completely reversible; close follow-up is essential even after discontinuation of culprit medications 6
• Inappropriate sinus tachycardia can occasionally induce Mobitz I AV block; rate control with ivabradine may be beneficial in such cases 7