What are the leading causes of bradycardia in pediatric patients?

Leading Causes of Bradycardia in Pediatric Patients

The leading causes of bradycardia in pediatric patients are congenital complete atrioventricular (AV) block, post-surgical AV block following congenital heart disease repair, sinus node dysfunction (particularly after atrial surgery), medication effects, neurocardiogenic mechanisms, and genetic channelopathies. 1

Primary Cardiac Causes

Congenital and Acquired AV Block

• Congenital complete AV block is a relatively rare but critical cause of bradycardia in children, often associated with maternal autoimmune disease or occurring as an isolated finding 1
• Post-surgical AV block represents a major cause, particularly after repair of congenital heart defects involving the ventricles (such as tetralogy of Fallot or ventricular septal defect 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 Dysfunction

• Sinus node disease is increasingly recognized in pediatric patients, especially following atrial surgery for congenital heart disease 1
• Sick sinus syndrome may be associated with specific genetic channelopathies but is not itself an indication for pacemaker implantation unless symptoms correlate with documented bradycardia 1
• The clinical significance is age-dependent: a heart rate of 45 bpm may be normal in an adolescent but represents profound bradycardia in a newborn or infant 1

Bradycardia-Tachycardia Syndrome

• This variant syndrome, where sinus bradycardia alternates with intra-atrial re-entrant tachycardia, is a significant problem after surgery for congenital heart disease 1
• Substantial morbidity and mortality have been observed with this condition, with loss of sinus rhythm being an independent risk factor 1
• Often requires combined therapy with antiarrhythmic medications (which may worsen bradycardia) and pacemaker support 1

Non-Cardiac Causes That Must Be Excluded

Medication Effects

• Antiarrhythmic drugs (sotalol, amiodarone, propranolol) used to control tachyarrhythmias can result in symptomatic bradycardia, particularly in children with bradycardia-tachycardia syndrome 1
• Prednisone can cause bradycardia in children, though this is less widely recognized; management involves dose reduction or discontinuation if symptomatic 2
• Drug effects must always be considered and excluded before attributing bradycardia to intrinsic cardiac disease 1

Neurocardiogenic and Autonomic Mechanisms

• Neurocardiogenic reflexes can cause transient but profound sinus pauses or sustained bradycardia resulting in syncope 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 1
• Carotid sinus hypersensitivity and autonomic dysfunction should be considered 1

Other Reversible Causes

• Apnea and autonomic immaturity, particularly in premature infants 1, 3
• Seizures themselves can cause bradycardia (ictal bradycardia/asystole occurs in 0.15-0.3% of epilepsy patients), or seizures may be confused with syncope from bradycardia 1, 4
• Central nervous system trauma 1
• Electrolyte imbalances and hypothyroidism 3
• Cardiac manifestations of anorexia nervosa 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 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

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

• Correlation of symptoms with bradycardia should be determined by ambulatory ECG or implantable loop recorder 1
• Bradycardia and associated symptoms in children are often transient (sinus arrest or paroxysmal AV block) and difficult to document 1
• All alternative reversible causes must be systematically excluded before attributing symptoms to intrinsic cardiac bradycardia requiring permanent pacing 1

Common Pitfalls to Avoid

• Do not use absolute heart rate criteria alone without considering age-appropriateness and symptom correlation 1
• Do not overlook medication effects, particularly in children on antiarrhythmic therapy for tachyarrhythmias 1
• Do not rush to pacemaker implantation without documenting symptom-bradycardia correlation and excluding reversible causes 1
• Do not assume all bradycardia is pathologic in trained adolescents or during sleep 1