Atrioventricular Block in Children

Introduction to Atrioventricular Block in Children

Atrioventricular (AV) block in children is a cardiac conduction disorder characterized by impaired electrical signal transmission from the atria to the ventricles. This condition can range from mild and asymptomatic to severe and life-threatening, depending on the degree of block and underlying cause. AV block in the pediatric population presents unique challenges in diagnosis and management due to its varied etiology and potential impact on growth and development.

The incidence of AV block in children is relatively low, with congenital complete heart block occurring in approximately 1 in 15,000 to 1 in 20,000 live births. Acquired AV block can occur at any age and may be associated with various conditions or interventions.

Etiology of Atrioventricular Block in Children

AV block in children can be categorized into congenital and acquired forms:

Congenital AV Block:

  • Maternal autoimmune diseases (e.g., Systemic Lupus Erythematosus, Sjögren's syndrome)
  • Structural heart defects (e.g., L-transposition of the great arteries, AV septal defects)
  • Genetic mutations affecting cardiac conduction system development

Acquired AV Block:

  • Post-cardiac surgery (especially involving the ventricular septum)
  • Infectious causes (e.g., myocarditis, Lyme disease, diphtheria)
  • Inflammatory conditions (e.g., Kawasaki disease, rheumatic fever)
  • Neuromuscular disorders (e.g., Duchenne muscular dystrophy)
  • Metabolic disorders (e.g., hypothyroidism, hyperkalemia)
  • Medications (e.g., beta-blockers, digoxin, certain antiarrhythmics)
  • Trauma (e.g., chest injury affecting the conduction system)

Classification of Atrioventricular Block in Children

AV block is typically classified into three degrees:

First-Degree AV Block:

Characterized by prolongation of the PR interval beyond the upper limit of normal for age. All atrial impulses are conducted to the ventricles, but with a delay.

Second-Degree AV Block:

  • Mobitz Type I (Wenckebach): Progressive prolongation of the PR interval until a ventricular beat is dropped.
  • Mobitz Type II: Intermittent non-conduction of atrial impulses to the ventricles without prior PR prolongation.
  • 2:1 AV Block: Every other P wave is conducted to the ventricles.

Third-Degree (Complete) AV Block:

Complete dissociation between atrial and ventricular activity. The ventricles are controlled by an escape rhythm, which can be junctional or ventricular in origin.

Clinical Presentation of Atrioventricular Block in Children

The clinical presentation of AV block in children varies widely depending on the degree of block, heart rate, and underlying etiology:

  • Asymptomatic: Often the case in first-degree and some second-degree AV blocks.
  • Fatigue and exercise intolerance: Particularly in higher degrees of block or when ventricular rates are inadequate.
  • Dizziness or syncope: May occur with sudden onset of high-grade AV block or in complete heart block with inadequate escape rhythm.
  • Palpitations: Can be present in any degree of AV block, often due to escape beats or rhythms.
  • Chest pain: Rarely reported, usually associated with underlying structural heart disease or myocarditis.
  • Shortness of breath: May occur with higher degrees of block, especially if associated with heart failure.
  • In infants: Poor feeding, irritability, pallor, or cyanosis may be observed in severe cases.

Physical examination findings may include:

  • Bradycardia: Especially notable in complete heart block.
  • Irregular pulse: Particularly in second-degree AV block.
  • Cannon A waves in the jugular venous pulse: Seen in complete heart block due to atrial contraction against closed AV valves.
  • Signs of heart failure: In severe cases or with underlying structural heart disease.

Diagnosis of Atrioventricular Block in Children

Diagnosis of AV block in children involves a combination of clinical assessment and diagnostic tests:

1. Electrocardiogram (ECG):

  • The primary diagnostic tool for AV block
  • Reveals PR interval prolongation, dropped beats, or AV dissociation
  • May show associated conduction abnormalities or chamber enlargement

2. Holter Monitor or Event Recorder:

  • Useful for detecting intermittent AV block
  • Helps correlate symptoms with rhythm disturbances
  • Assesses heart rate variability and minimum heart rate

3. Exercise Stress Test:

  • Evaluates AV conduction during increased heart rates
  • Assesses chronotropic competence and exercise tolerance

4. Echocardiogram:

  • Identifies associated structural heart defects
  • Assesses ventricular function and any signs of cardiomyopathy

5. Laboratory Tests:

  • Electrolyte panel: To rule out metabolic causes
  • Thyroid function tests: To exclude hypothyroidism
  • Autoimmune markers: In cases of suspected maternal autoimmune disease
  • Lyme titers: If Lyme carditis is suspected

6. Genetic Testing:

  • May be considered in familial cases or when genetic syndromes are suspected

7. Electrophysiology Study:

  • Rarely needed in children, but may be useful in complex cases
  • Can help determine the level of block and assess other conduction abnormalities

Management of Atrioventricular Block in Children

Management of AV block in children depends on the degree of block, underlying cause, and clinical presentation:

1. Observation:

  • Appropriate for asymptomatic first-degree and some cases of second-degree AV block
  • Regular follow-up with serial ECGs and Holter monitoring

2. Treatment of Underlying Cause:

  • Correction of electrolyte imbalances
  • Management of hypothyroidism
  • Antibiotic therapy for infectious causes (e.g., Lyme disease)
  • Adjustment or discontinuation of causative medications

3. Pharmacological Interventions:

  • Atropine: For acute management of symptomatic bradycardia
  • Isoproterenol: Can be used as a bridge to pacemaker implantation in symptomatic complete heart block

4. Pacemaker Implantation:

Indications for pacemaker implantation in children include:

  • Symptomatic bradycardia
  • Complete AV block with wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction
  • Complete AV block with average heart rate <50 bpm in infants or <40 bpm in children/adolescents
  • Advanced second-degree AV block associated with symptomatic bradycardia

Pacemaker considerations in children:

  • Epicardial vs. transvenous systems: Epicardial preferred in small children or those with intracardiac shunts
  • Need for frequent reprogramming to accommodate growth and changing activity levels
  • Long-term considerations including lead longevity and vascular access preservation

5. Catheter Ablation:

  • Rarely indicated in children with AV block
  • May be considered in cases of AV block due to accessory pathways

6. Lifestyle Modifications:

  • Activity restrictions may be necessary in symptomatic patients awaiting intervention
  • Counseling regarding symptoms that warrant immediate medical attention

Prognosis of Atrioventricular Block in Children

The prognosis of AV block in children varies depending on the underlying cause, degree of block, and management approach:

First-Degree AV Block:

  • Generally has an excellent prognosis
  • Rarely progresses to higher degrees of block
  • Regular monitoring is usually sufficient

Second-Degree AV Block:

  • Mobitz Type I: Often benign, especially if asymptomatic
  • Mobitz Type II: Higher risk of progression to complete heart block
  • Prognosis depends on the underlying cause and presence of structural heart disease

Complete (Third-Degree) AV Block:

  • Congenital: Generally good long-term prognosis with appropriate pacemaker therapy
  • Acquired: Prognosis varies based on etiology; may resolve if the underlying cause is treated

Factors Affecting Prognosis:

  • Age at onset: Earlier onset may be associated with more complex management
  • Presence of structural heart disease: Can complicate management and affect long-term outcomes
  • Adequacy of escape rhythm: Stable, narrow-complex escape rhythms have better prognosis than wide-complex or unstable rhythms
  • Timely intervention: Early recognition and appropriate management improve outcomes

Long-Term Considerations:

  • Need for lifelong follow-up, especially in pacemaker-dependent patients
  • Potential for pacemaker-related complications (e.g., lead fracture, infection)
  • Impact on quality of life and physical activity, particularly in competitive athletes
  • Pregnancy considerations for female patients with congenital heart block

Overall, with appropriate management and follow-up, most children with AV block can lead normal, active lives. However, ongoing cardiac care and monitoring are essential to ensure optimal long-term outcomes.

First-Degree AV Block

Definition:

First-degree AV block is characterized by a prolonged PR interval (>200 ms in children) with all atrial impulses being conducted to the ventricles.

Electrophysiology:

  • Delay in conduction can occur in the atrium, AV node, His bundle, or bundle branches
  • Most commonly, the delay is within the AV node

ECG Characteristics:

  • Prolonged PR interval (>200 ms in children, age-dependent)
  • 1:1 AV conduction (every P wave followed by a QRS complex)
  • Normal QRS morphology (unless there's coexisting bundle branch block)

Etiology in Children:

  • Often a normal variant, especially in athletes
  • Increased vagal tone
  • Congenital heart defects (e.g., ASD, VSD)
  • Medications (e.g., beta-blockers, digoxin)
  • Electrolyte disturbances (e.g., hyperkalemia)
  • Inflammatory conditions (e.g., myocarditis, Lyme disease)

Clinical Significance:

  • Usually asymptomatic and benign
  • Rarely progresses to higher degrees of AV block
  • May be the first sign of a developing conduction system disease

Management:

  • Generally, no specific treatment is required
  • Address underlying causes if identified
  • Regular follow-up with serial ECGs
  • Consider Holter monitoring to assess for progression

Prognosis:

Excellent in most cases. Rarely associated with adverse outcomes unless there's underlying structural heart disease or progression to higher degrees of block.

Second-Degree AV Block: Mobitz Type I (Wenckebach)

Definition:

Mobitz Type I, also known as Wenckebach periodicity, is characterized by progressive prolongation of the PR interval until an atrial impulse fails to conduct to the ventricles.

Electrophysiology:

  • Usually occurs within the AV node
  • Progressive delay in each subsequent impulse until a complete block occurs
  • After the blocked beat, the cycle repeats

ECG Characteristics:

  • Progressive prolongation of PR interval
  • Shortening of RR intervals within the cycle
  • Dropped QRS complex after the longest PR interval
  • Often follows a predictable pattern (e.g., 3:2, 4:3, 5:4)

Etiology in Children:

  • Increased vagal tone (common in well-trained young athletes)
  • Post-cardiac surgery (especially involving the AV node region)
  • Inflammatory conditions (e.g., myocarditis, rheumatic fever)
  • Medications (e.g., beta-blockers, digoxin, calcium channel blockers)
  • Congenital heart defects
  • Infectious diseases (e.g., Lyme disease)

Clinical Significance:

  • Often asymptomatic, especially when occurring during sleep
  • May cause palpitations, dizziness, or fatigue if heart rate drops significantly
  • Usually benign when occurring at the AV node level

Management:

  • Asymptomatic patients often require no specific treatment
  • Identify and treat underlying causes
  • For symptomatic patients:
    • Atropine for acute management
    • Consider temporary pacing if severely symptomatic
    • Permanent pacing rarely needed in children
  • Regular follow-up with ECGs and Holter monitoring

Prognosis:

Generally good, especially when occurring at the AV node level. Rarely progresses to complete heart block. Prognosis may be affected by underlying cardiac conditions.

Second-Degree AV Block: Mobitz Type II

Definition:

Mobitz Type II is characterized by intermittent non-conduction of atrial impulses to the ventricles without prior PR interval prolongation.

Electrophysiology:

  • Usually occurs below the AV node (in the His bundle or bundle branches)
  • Abrupt failure of conduction without prior prolongation

ECG Characteristics:

  • Constant PR interval in conducted beats
  • Sudden dropped QRS complexes without PR prolongation
  • Often associated with bundle branch block
  • Can have a fixed ratio of conduction (e.g., 2:1, 3:1)

Etiology in Children:

  • Congenital heart defects (especially those involving the conduction system)
  • Post-cardiac surgery (particularly involving the septum)
  • Inflammatory conditions (e.g., myocarditis)
  • Neuromuscular disorders
  • Infiltrative diseases
  • Rarely, idiopathic degeneration of the conduction system

Clinical Significance:

  • Generally more concerning than Mobitz Type I
  • Higher risk of progression to complete heart block
  • May cause significant bradycardia, especially with exercise
  • Symptoms may include syncope, presyncope, fatigue, and exercise intolerance

Management:

  • Often requires more aggressive management than Mobitz Type I
  • Continuous cardiac monitoring
  • Treat underlying causes if identified
  • Temporary pacing may be needed in acute settings
  • Permanent pacemaker implantation is often indicated, especially if:
    • Symptomatic bradycardia
    • Wide QRS complex
    • Associated with structural heart disease

Prognosis:

More guarded than Mobitz Type I. Higher risk of progression to complete heart block. With appropriate management, including pacemaker implantation when indicated, prognosis can be good. Long-term outcomes depend on underlying cardiac status and associated conditions.

High-Grade Second-Degree AV Block

Definition:

High-grade second-degree AV block is characterized by two or more consecutive P waves that are not conducted to the ventricles. It includes 2:1 AV block and higher degrees of block (e.g., 3:1, 4:1).

Electrophysiology:

  • Can occur at any level of the conduction system
  • Multiple consecutive atrial impulses fail to conduct
  • May represent a transitional state between second-degree and complete heart block

ECG Characteristics:

  • Regular or irregular rhythm depending on the conduction ratio
  • Multiple consecutive P waves without following QRS complexes
  • In 2:1 block, every other P wave is followed by a QRS complex
  • QRS morphology can be narrow or wide, depending on the level of block

Etiology in Children:

  • Congenital heart defects
  • Post-cardiac surgery
  • Myocarditis
  • Cardiomyopathies
  • Medications (e.g., high-dose beta-blockers)
  • Lyme carditis
  • Progression of lower grade AV block

Clinical Significance:

  • Often symptomatic due to significant bradycardia
  • Symptoms may include syncope, presyncope, fatigue, and exercise intolerance
  • Risk of sudden progression to complete heart block
  • Can lead to ventricular escape rhythms

Management:

  • Immediate evaluation and monitoring
  • Treat underlying causes if identified
  • Temporary pacing may be necessary in acute settings
  • Permanent pacemaker implantation is often indicated, especially if:
    • Symptomatic bradycardia
    • Wide QRS complexes
    • Associated with structural heart disease
    • Persistent or recurrent high-grade block
  • Close follow-up with serial ECGs and Holter monitoring

Prognosis:

Generally more serious than lower grades of AV block. Risk of progression to complete heart block is significant. With appropriate management, including timely pacemaker implantation when indicated, prognosis can be favorable. Long-term outcomes depend on underlying cardiac status, associated conditions, and the effectiveness of interventions.

Third-Degree (Complete) AV Block

Definition:

Third-degree AV block, also known as complete heart block, is characterized by a complete dissociation between atrial and ventricular activity, with no conduction of atrial impulses to the ventricles.

Electrophysiology:

  • Complete interruption of conduction between atria and ventricles
  • Ventricles are controlled by an escape pacemaker (junctional or ventricular)
  • Can occur at AV node, His bundle, or infra-Hisian level

ECG Characteristics:

  • Complete dissociation of P waves and QRS complexes
  • Regular P waves at a rate faster than QRS complexes
  • QRS complexes are regular but typically slow
  • QRS morphology depends on the site of the escape pacemaker:
    • Narrow if junctional escape
    • Wide if ventricular escape

Etiology in Children:

  • Congenital:
    • Maternal autoimmune diseases (e.g., lupus, Sjögren's syndrome)
    • Structural heart defects (e.g., L-transposition of great arteries)
    • Genetic mutations affecting the conduction system
  • Acquired:
    • Post-cardiac surgery
    • Myocarditis
    • Lyme disease
    • Cardiomyopathies
    • Muscular dystrophies
    • Progression from lower grades of AV block

Clinical Significance:

  • Often symptomatic, especially if ventricular rate is very slow
  • Symptoms may include syncope, presyncope, fatigue, exercise intolerance
  • Risk of sudden cardiac death, particularly with wide QRS escape rhythms
  • In neonates, can present with hydrops fetalis or congestive heart failure

Management:

  • Immediate evaluation and continuous cardiac monitoring
  • Treat underlying causes if identified
  • Temporary pacing is often necessary in acute settings
  • Permanent pacemaker implantation is typically indicated:
    • In all symptomatic patients
    • In asymptomatic patients with risk factors (e.g., wide QRS, low escape rate, structural heart disease)
    • In most congenital complete heart block cases
  • Choice of pacing mode (dual chamber vs. single chamber) depends on patient age, size, and anatomy
  • Long-term follow-up with regular device checks and ECGs

Prognosis:

Prognosis varies depending on underlying cause and management:

  • Congenital complete heart block: Generally good long-term prognosis with appropriate pacing
  • Acquired complete heart block: Prognosis depends on the underlying cause:
    • Post-surgical: May be transient with good prognosis if resolves, or may require permanent pacing
    • Inflammatory causes (e.g., myocarditis): Can potentially resolve with treatment of underlying condition
    • Neuromuscular disorders: Prognosis tied to the underlying disease progression
  • Factors affecting long-term prognosis:
    • Age at diagnosis and initiation of treatment
    • Presence of structural heart disease
    • Adequacy of rate control with pacing
    • Development of pacemaker-related complications

Special Considerations in Children:

  • Growth and Development:
    • Pacemaker settings need frequent adjustment to accommodate growth
    • Lead placement strategies must account for future growth
  • Physical Activity:
    • Most children with well-managed complete heart block can participate in sports
    • Individualized recommendations based on underlying heart disease and pacemaker dependence
  • Psychological Impact:
    • Need for lifelong medical care and device dependence can affect quality of life
    • Importance of age-appropriate education and psychological support
  • Transition to Adult Care:
    • Planning for transition should begin in early adolescence
    • Ensure understanding of condition, self-management skills, and importance of follow-up

Emerging Therapies and Future Directions:

  • Leadless Pacemakers:
    • Potential for reduced complications related to transvenous leads
    • Currently limited by size and battery longevity for pediatric use
  • Biological Pacemakers:
    • Research into gene therapy and cell-based approaches to create biological pacemakers
    • Potential to overcome limitations of electronic devices in growing children
  • Improved Risk Stratification:
    • Development of better predictors for progression of AV block in children
    • Potential for more targeted interventions and follow-up strategies
  • Advanced Imaging Techniques:
    • Use of cardiac MRI and other modalities to better understand the anatomy and pathophysiology of conduction disorders
    • Potential for improved diagnosis and management strategies

Long-term Follow-up:

  • Regular pacemaker checks (typically every 3-6 months)
  • Annual echocardiograms to assess ventricular function
  • Periodic exercise testing to ensure adequate rate response
  • Monitoring for potential complications:
    • Lead fracture or dislodgement
    • Infection
    • Venous occlusion (with transvenous systems)
    • Pacemaker syndrome
  • Ongoing assessment of cognitive and psychosocial development
  • Family education and support

Conclusion:

Third-degree AV block in children presents unique challenges in diagnosis, management, and long-term care. While it can be a serious condition, advancements in pacemaker technology and improved understanding of the condition have greatly enhanced outcomes. With appropriate management, most children with complete heart block can lead normal, active lives. However, lifelong follow-up and a multidisciplinary approach to care are essential to ensure optimal outcomes and quality of life.



Objective QnA: Atrioventricular Block in Children
  1. What is the primary function of the atrioventricular (AV) node?
    To delay electrical impulses between the atria and ventricles
  2. Which type of AV block is characterized by a prolonged PR interval?
    First-degree AV block
  3. In second-degree AV block type I (Wenckebach), what happens to the PR interval?
    It progressively lengthens until a QRS complex is dropped
  4. What is the hallmark of second-degree AV block type II (Mobitz II)?
    Intermittent failure of AV conduction without PR prolongation
  5. Which type of AV block is most commonly associated with congenital heart defects?
    Third-degree (complete) AV block
  6. What is the most common cause of acquired complete AV block in children?
    Surgical intervention for congenital heart disease
  7. Which autoimmune condition is associated with congenital complete AV block?
    Neonatal lupus erythematosus
  8. What is the primary treatment for symptomatic complete AV block in children?
    Permanent pacemaker implantation
  9. Which medication can cause AV block as a side effect in children?
    Beta-blockers
  10. What is the typical heart rate in a child with complete AV block?
    40-80 beats per minute
  11. Which imaging modality is most useful for diagnosing the etiology of AV block in children?
    Echocardiography
  12. What percentage of children with congenital complete AV block require pacemaker implantation by adulthood?
    Approximately 65%
  13. Which electrolyte imbalance can exacerbate AV block?
    Hyperkalemia
  14. What is the most common symptom of AV block in children?
    Fatigue
  15. Which viral infection is associated with transient AV block in children?
    Lyme disease
  16. What is the Stokes-Adams attack in the context of AV block?
    Sudden loss of consciousness due to ventricular asystole
  17. Which congenital heart defect is most commonly associated with AV block?
    L-transposition of the great arteries
  18. What is the role of exercise testing in children with AV block?
    To assess chronotropic competence and exercise-induced higher degree block
  19. Which type of AV block is most likely to progress to complete heart block?
    Second-degree AV block type II (Mobitz II)
  20. What is the typical management approach for asymptomatic first-degree AV block in children?
    Observation without intervention
  21. Which cardiac structure is most commonly affected in congenital AV block?
    The AV node
  22. What is the role of temporary pacing in managing AV block in children?
    To stabilize patients with symptomatic bradycardia before permanent pacemaker implantation
  23. Which surgical procedure for congenital heart disease carries the highest risk of postoperative AV block?
    Ventricular septal defect closure
  24. What is the most common mode of pacing used in children with complete AV block?
    DDD (dual chamber pacing and sensing)
  25. Which diagnostic test is essential for differentiating between second-degree AV block type I and type II?
    12-lead ECG
  26. What is the significance of a wide QRS complex in a child with complete AV block?
    It indicates a lower (ventricular) escape rhythm
  27. Which medication can be used to temporarily increase heart rate in symptomatic AV block?
    Atropine
  28. What is the recommended follow-up interval for children with asymptomatic second-degree AV block?
    Every 3-6 months
  29. Which conduction system disease is often associated with familial AV block in children?
    Progressive cardiac conduction disease (Lenègre disease)
  30. What is the primary goal of managing AV block in children?
    To prevent symptoms and sudden cardiac death


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