What is the management approach for a patient with infranodal (below the atrioventricular node) block?

Management of Infranodal Block

Patients with infranodal atrioventricular block should receive permanent pacemaker implantation, as this condition represents a high risk for progression to complete heart block and sudden death. 1

Understanding Infranodal Block

Infranodal block refers to conduction disturbances occurring below the atrioventricular (AV) node in the His-Purkinje system. Unlike AV nodal blocks, infranodal blocks:

• Indicate disease in the distal conduction system
• Can progress rapidly and unpredictably to complete heart block
• Are associated with higher risk of sudden death 1
• Often present with a wide-complex escape rhythm when complete

Diagnostic Approach

When infranodal block is suspected:

1. ECG findings suggestive of infranodal block:

   • Wide QRS complex
   • Bundle branch blocks (especially alternating bundle branch block)
   • PR interval may be normal or prolonged

2. Electrophysiological study (EPS) is valuable to:

   • Confirm infranodal location (HV interval ≥70 ms)
   • Assess risk of progression to complete heart block 1

3. Ambulatory monitoring to document:

   • Intermittent higher-degree block
   • Progression of conduction disease

Management Algorithm

Immediate Management:

1. For symptomatic patients (syncope, pre-syncope):

   • Immediate hospitalization for cardiac monitoring
   • Temporary pacing if hemodynamically unstable
   • Avoid atropine as it is contraindicated in infranodal block and may worsen the block 1, 2

2. For asymptomatic patients with evidence of infranodal block:

   • Cardiac monitoring
   • Expedited evaluation for permanent pacing

Definitive Management:

Class I indications for permanent pacing (highest recommendation):

• Infranodal block with syncope 1
• Infranodal block with HV interval ≥70 ms on EPS 1
• Alternating bundle branch block (strong predictor of progression) 1
• Infranodal block in the setting of acute MI 1

Class IIa indications (reasonable to perform):

• Infranodal block with symptoms even without documented progression 1
• Kearns-Sayre syndrome with conduction disorders 1

Pacing modality considerations:

• His bundle pacing or left bundle branch area pacing may be preferable to right ventricular pacing when technically feasible 3
• Consider additional defibrillator capability if reduced left ventricular function is present 1

Special Considerations

1. Acute myocardial infarction context:

   • Infranodal block in anterior MI indicates extensive myocardial damage
   • Permanent pacing is indicated even if transient during the acute phase 1
   • Avoid early permanent pacing (<72 hours) to allow for potential recovery 1

2. Medication precautions:

   • Avoid atropine in infranodal block as it may worsen the block 1
   • Avoid drugs that slow conduction (beta-blockers, calcium channel blockers, digoxin)

3. AV nodal ablation context:

   • When performing AV nodal ablation for rate control in atrial fibrillation, permanent pacing is mandatory 1
   • Consider cardiac resynchronization therapy in patients with heart failure 1

Prognosis and Follow-up

• Infranodal block has a higher risk of progression to complete heart block compared to AV nodal block 1
• Recent studies suggest that true infra-Hisian block (most distal form) is relatively rare, with most infranodal blocks being intra-Hisian 3
• After pacemaker implantation, routine device checks are essential to ensure proper function

Common Pitfalls to Avoid

1. Misdiagnosing the level of block: Incorrectly identifying an infranodal block as AV nodal can lead to inappropriate treatment with atropine, which may worsen the block 1

2. Delaying permanent pacing: Given the unpredictable and potentially rapid progression to complete heart block, delays in pacemaker implantation can be life-threatening 1

3. Overlooking underlying structural heart disease: Infranodal block often indicates more extensive cardiac pathology that may require additional intervention beyond pacing 1