Definition & Classification
Disturbance in electrical impulse conduction from atria through atrioventricular (AV) node to ventricles. Spectrum ranges from transmission delay to complete electrical dissociation.
| Block Type | Electrocardiographic (ECG) Features | Clinical Characteristics |
|---|---|---|
| First-Degree AV Block | PR interval prolonged beyond upper normal limit for age. | Asymptomatic. 8% prevalence in normal children secondary to increased vagal tone. |
| Second-Degree (Mobitz I / Wenckebach) | Progressive PR prolongation terminating in non-conducted P-wave. | Block at AV node level. Normal during sleep (high parasympathetic tone) or in athletes. |
| Second-Degree (Mobitz II) | Stable PR interval preceding non-conducted P-wave. | Block at or below AV node (His-Purkinje). High risk of progression to complete block. |
| Second-Degree (High-Grade) | Two or more consecutive non-conducted P-waves. | Suggests significant disease below AV node. |
| Third-Degree (Complete Heart Block - CHB) | Complete AV dissociation. Regular ventricular escape rhythm independent of atrial rate. | Absence of impulse conduction to ventricles. High risk for syncope, sudden death, or fetal hydrops,. |
Etiology & Associations
| Category | Etiologies & High-Yield Associations |
|---|---|
| Autoimmune (Congenital) | Transplacental transfer of maternal IgG antibodies (+SSA/Ro, +SSB/La) in Systemic Lupus Erythematosus (SLE) or Sjögren syndrome,. Accounts for 60–70% of congenital CHB. Represents 80% of cases with structurally normal hearts. |
| Structural CHD | Left atrial isomerism (Heterotaxy) (absent/abnormal SA node). Congenitally corrected transposition of great arteries (ccTGA) (40% incidence, increases 2% annually). Atrioventricular canal defects. |
| Genetic / Familial | Familial AV Block (FAVB) linked to SCN5A variants (sodium channel) or Connexin 40. NKX2-5 mutations associated with CHB and Atrial Septal Defect (ASD). |
| Postoperative (Acquired) | 1–3% incidence following congenital cardiac surgery. Highest risk procedures involve VSD, AV canal, tetralogy of Fallot, ccTGA, and heterotaxy repairs. Transient AV block (5–10% of cases) resolves within 7–10 days. |
| Infectious / Inflammatory | Viral myocarditis, Lyme carditis (heart block seen in 4-10% of cases), acute rheumatic fever, Chagas disease,,. |
| Pharmacologic | Digoxin, beta-blockers, calcium channel blockers, clonidine, amiodarone, lithium,. |
Clinical Presentation
Fetal Presentation
- Diagnosed primarily between 17–28 weeks gestation.
- Fetal heart rate <50 beats per minute (bpm) indicates poor prognosis,.
- Associated with hydrops fetalis.
- Immune-mediated endocardial fibroelastosis (EFE) or ventricular dysfunction present in 15–20% of autoimmune cases.
Infant and Toddler Presentation
- Irritability, tiredness, frequent naps, night terrors.
- Prominent peripheral pulses secondary to compensatory large stroke volume and peripheral vasodilation.
- Elevated systolic blood pressure.
- Irregular, large jugular venous pulsations (cannon ‘a’ waves) resulting from atrial contraction against closed tricuspid valve.
- Variable first heart sound.
- Apical mid-diastolic murmurs often auscultated.
Older Child and Adolescent Presentation
- Often asymptomatic at rest.
- Exertional fatigue or dyspnea,.
- Dizziness, syncope (Stokes-Adams attacks).
- Sudden cardiac death risk.
Diagnostic Evaluation
- 12-Lead Electrocardiogram (ECG): Confirms dissociation of P waves and QRS complexes in CHB. QRS duration normal (<120 ms) if block located high in AV node/Bundle of His,. Wide QRS suggests distal block location.
- 24-Hour Ambulatory ECG (Holter): Assesses average diurnal heart rate, longest ventricular pauses, and occult ventricular ectopy.
- Echocardiography: Excludes associated structural heart disease (e.g., ccTGA, heterotaxy). Evaluates ventricular function and rules out EFE,.
- Maternal Serology: Anti-SSA/Ro and anti-SSB/La antibody testing mandated for unexplained fetal or neonatal AV block.
- Genetic Testing: Indicated in Familial AV block without evidence of maternal autoimmune disease.
Management & Interventions
Fetal Heart Block Management
- Corticosteroids (Dexamethasone): Crosses placenta. Indicated (4–8 mg/day) to decrease conduction system inflammation. Utilized for second-degree heart block, new-onset CHB, hydrops, or cardiac dysfunction,. Efficacy in reversing established CHB remains controversial.
- Intravenous Immunoglobulin (IVIG): 1 g/kg every 2–3 weeks. Indicated for fetal ventricular dysfunction or EFE.
- Beta-Sympathomimetics: Terbutaline or salbutamol utilized to increase fetal heart rates <55–60 bpm. Controversial efficacy; fails to demonstrate proven survival benefit and risks maternal ectopy.
Acute Symptomatic Bradycardia (Hemodynamic Compromise)
- Follow Pediatric Advanced Life Support (PALS) algorithms.
- Initiate cardiopulmonary resuscitation (CPR) if heart rate <60 bpm with poor perfusion despite oxygenation and ventilation.
- Epinephrine: 0.01 mg/kg IV/IO.
- Atropine: 0.02 mg/kg (Minimum: 0.1 mg; Maximum: 1 mg). Indicated for increased vagal tone or primary AV block.
- Cardiac Pacing: Temporary transvenous or transcutaneous pacing indicated if pharmacologic measures fail.
Permanent Pacing Indications
Guidelines direct permanent cardiac rhythm device implantation based on chronicity, symptoms, and associated anomalies.
Class I Indications (Definitive Need)
- Symptomatic bradycardia with any degree of AV block,.
- Congenital complete AV block accompanied by wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction,.
- Postoperative high-grade second-degree or third-degree AV block not expected to resolve (typically evaluated >10–14 days post-surgery),,.
- Mobitz Type II second-degree AV block with wide QRS.
Class IIa Indications (Reasonable to Perform)
- Congenital complete AV block with average daytime resting heart rate <50 bpm in adults/adolescents.
- Neonatal complete AV block with resting ventricular rate <55 bpm.
- Complex congenital heart disease with awake resting heart rate <40 bpm or ventricular pauses >3 seconds.
- Impaired hemodynamics secondary to loss of AV synchrony.
Surgical Considerations
- Epicardial pacing systems required for patients lacking systemic venous access to heart (e.g., post-Fontan or Glenn palliation).
- Endocardial (transvenous) leads avoided in presence of right-to-left intracardiac shunting due to paradoxical embolic stroke risk,.
Sports Participation & Restrictions
- First-Degree / Mobitz I (Wenckebach): No competitive sports restrictions if asymptomatic and structurally normal heart.
- Complete Right/Left Bundle Branch Block: No restriction if asymptomatic, structurally normal heart, and absence of rate-dependent progression to complete block,.
- Congenital Complete Heart Block: Contraindicated for competitive sports unless permanent pacemaker implanted. Post-implantation exercise stress testing required to ensure appropriate chronotropic response and normal HV interval.