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