Causes of Bradycardia in Children
Primary Cardiac Causes
Congenital complete atrioventricular (AV) block is a critical cardiac cause of bradycardia in children, often linked to maternal autoimmune disease (anti-Ro/anti-La antibodies) or occurring as an isolated congenital finding. 1
Conduction System Abnormalities
Post-surgical AV block represents a major cause of bradycardia, particularly after repair of congenital heart defects involving the ventricles (e.g., ventricular septal defect closure, tetralogy of Fallot repair), with permanent pacing indicated if block persists beyond 7-10 days postoperatively. 1
Advanced second-degree or third-degree AV block carries substantial morbidity and mortality risk, requiring permanent pacing when associated with symptomatic bradycardia, ventricular dysfunction, or low cardiac output. 1
Sinus node disease is increasingly recognized in pediatric patients, especially following atrial surgery for congenital heart disease (e.g., Fontan procedure, Mustard/Senning operations for transposition of great arteries), and may be associated with specific genetic channelopathies. 1
Structural Heart Disease Considerations
Children with congenital heart disease and residual impaired ventricular function may develop symptoms from bradycardia at heart rates that would not produce symptoms in those with normal cardiovascular physiology—the clinical significance depends on the underlying hemodynamic state rather than absolute heart rate alone. 1
The presence of structural heart disease significantly increases the clinical significance of bradycardia, with pacemaker indicated for infants with heart rate <70 bpm when associated with structural heart disease (versus <55 bpm in structurally normal hearts). 1
Non-Cardiac Causes (Must Be Excluded First)
Medication-Induced Bradycardia
Antiarrhythmic drugs (sotalol, amiodarone, propranolol) used to control tachyarrhythmias can result in symptomatic bradycardia, particularly in children with bradycardia-tachycardia syndrome. 1
Digoxin can produce sinus bradycardia and various degrees of AV block, especially in infants and children where cardiac arrhythmias (including sinus bradycardia) are the earliest and most frequent manifestation of excessive dosing rather than gastrointestinal symptoms. 2
Beta-blockers, calcium channel blockers, and other cardiac medications must be systematically reviewed and excluded as reversible causes before attributing bradycardia to intrinsic cardiac disease. 1
Autonomic and Reflex Mechanisms
Neurocardiogenic reflexes can cause transient but profound sinus pauses or sustained bradycardia resulting in syncope, representing a common non-cardiac mechanism in children. 1
Breath-holding spells (pallid type) associated with profound bradycardia or asystole occur in 2-5% of well children and can cause recurrent seizures and syncope; cardiac pacing has been effective in carefully selected cases with recurrent pallid breath-holding spells. 1, 3
Vagal stimulation from various sources (suctioning, intubation, increased intracranial pressure) can trigger bradycardia, particularly in neonates and infants. 4
Metabolic and Systemic Causes
Hypothyroidism can cause sinus bradycardia and must be excluded through thyroid function testing. 5
Electrolyte imbalances (hyperkalemia, hypocalcemia, hypomagnesemia) represent reversible causes that must be corrected before attributing bradycardia to intrinsic cardiac pathology. 5
Hypothermia produces dose-dependent bradycardia and should be identified and corrected. 5
Hypoxemia and respiratory failure can trigger bradycardia, particularly in neonates and young infants with autonomic immaturity. 5
Age-Specific Considerations
Autonomic immaturity in premature infants is a common non-pathologic cause of bradycardia, typically self-resolving as the infant matures. 5
Apnea of prematurity frequently presents with associated bradycardia in preterm neonates. 3
Genetic and Channelopathies
Genetic variants in multiple genes have been described in the pathogenesis of inherited sinus node dysfunction or progressive cardiac conduction disorders, though specific genetic testing is typically reserved for cases with family history or unexplained conduction disease. 6
Long QT syndrome and other channelopathies may present with bradycardia, particularly pause-dependent arrhythmias, and should be considered when bradycardia is associated with syncope or family history of sudden death. 3
Bradycardia-Tachycardia Syndrome
A variant of bradycardia-tachycardia syndrome—sinus bradycardia alternating with intra-atrial re-entrant tachycardia—is a significant problem after surgery for congenital heart disease, with substantial morbidity and mortality observed in patients with recurrent or chronic intra-atrial re-entrant tachycardia. 3
The loss of sinus rhythm is an independent risk factor for the subsequent development of atrial tachyarrhythmias in post-surgical congenital heart disease patients. 3
Critical Diagnostic Approach
The primary criterion for intervention is concurrent observation of symptoms (syncope, inappropriate weakness, dyspnea) with documented bradycardia (heart rate <40 bpm or asystole >3 seconds), rather than absolute heart rate criteria alone. 1
Essential Diagnostic Steps
Correlation of symptoms with bradycardia should be determined by ambulatory ECG monitoring (24-hour Holter) or implantable loop recorder to establish a temporal relationship between bradycardia and clinical manifestations. 1, 5
All alternative reversible causes must be systematically excluded before attributing symptoms to intrinsic cardiac bradycardia requiring permanent pacing—this includes medication review, metabolic screening, thyroid function, and assessment for neurocardiogenic mechanisms. 1
12-lead ECG is essential to identify conduction abnormalities, AV block patterns, and features suggestive of channelopathies. 5
Echocardiography is indicated to assess for structural heart disease, ventricular function, and congenital anomalies. 5
Common Pitfalls to Avoid
Do not use absolute heart rate criteria alone to determine clinical significance in children with congenital heart disease—symptoms must correlate with relative bradycardia in the context of their underlying physiology. 3, 1
Do not overlook medication effects, particularly in children on antiarrhythmics for tachycardia management; digoxin toxicity in children presents primarily with arrhythmias (including sinus bradycardia) rather than gastrointestinal symptoms seen in adults. 2
Do not attribute transient bradycardia to intrinsic cardiac disease without excluding apnea, seizures, medication effects, and neurocardiogenic mechanisms through appropriate monitoring and testing. 3
Recognize that age-dependent normal values differ significantly—a heart rate of 45 bpm may be normal in an adolescent but indicates profound bradycardia in a newborn or infant. 3
Do not delay evaluation of exertional syncope with bradycardia, as this may represent life-threatening conditions such as long QT syndrome or structural heart disease requiring urgent intervention. 7