What are the diagnostic criteria for congenital complete heart block (CHB)?

Diagnostic Criteria for Congenital Complete Heart Block (CHB)

Congenital complete heart block is diagnosed by electrocardiographic demonstration of complete absence of conduction from atrium to ventricle, with normal atrial activation and slower dissociated regular QRS complexes, occurring in utero or within the first 27 days of life. 1

ECG Diagnostic Features

• Complete dissociation between atrial and ventricular activity
• Normal P waves with regular rhythm
• Slower, regular QRS complexes that are independent of atrial activity
• QRS duration varies based on age:

  • 90 ms in children less than 4 years of age

  • 100 ms in children 4-16 years of age

  • ≥120 ms in adults 1

Epidemiology and Etiology

Congenital CHB occurs in approximately 1 in 15,000 to 20,000 live births 1, 2 and has two primary etiologies:

1. Immune-mediated CHB:

   • Associated with maternal autoantibodies (anti-Ro/SSA and anti-La/SSB)
   • Transplacental passage of these antibodies damages fetal cardiac conduction tissue
   • Most mothers (>70%) are asymptomatic carriers without diagnosed rheumatologic disease 2

2. Structural CHB:

   • Associated with congenital heart malformations
   • Results from abnormal development of the conduction tissue 1

Clinical Presentation and Assessment

• In utero: Detected by fetal bradycardia during routine obstetric ultrasound
• Neonatal period: Bradycardia with heart rates typically:
  • <55 bpm at rest in infants
  • <70 bpm when associated with structural heart disease 1
• Symptoms may include:
  • Poor feeding
  • Lethargy
  • Signs of heart failure
  • Syncope (in older children)

Diagnostic Workup

1. Electrocardiogram (ECG):

   • Confirms complete AV block with atrial-ventricular dissociation
   • Assesses QRS duration and morphology
   • Evaluates for associated conduction abnormalities 1

2. Echocardiogram:

   • Essential for all neonates with CHB
   • Evaluates for structural heart disease
   • Assesses ventricular function 1

3. Maternal Antibody Testing:

   • Anti-Ro/SSA and anti-La/SSB antibodies
   • Important even in asymptomatic mothers 2

4. Family Screening:

   • ECG should be performed on parents and siblings to identify familial conduction disorders 1

Risk Stratification

The highest mortality risk occurs during the first 3 months of life 1. Risk factors for poor outcomes include:

• Heart rate <55 bpm in infants
• Heart rate <70 bpm with structural heart disease
• Wide QRS complexes
• Prolonged QT interval
• Left ventricular dysfunction
• Presence of associated structural heart disease 1

Common Pitfalls in Diagnosis

• Misdiagnosing functional 2:1 AV block in the setting of long QT syndrome as complete CHB
• Failing to identify maternal autoimmune disease in asymptomatic mothers
• Not distinguishing between congenital CHB (present at birth) and acquired CHB that develops later in life
• Overlooking the need for regular follow-up of ventricular function, as paced patients may develop dilated cardiomyopathy years after pacemaker implantation 2

Conclusion

Early and accurate diagnosis of congenital CHB is critical for appropriate management and improved outcomes. The diagnostic criteria focus on electrocardiographic confirmation of complete AV dissociation in the fetal or neonatal period, with additional workup to determine etiology and associated conditions.