Paediatric Tachyarrhythmias

Introduction

• Rapid heart rate in children may be due to:
  • Sinus tachycardia
  • SVT
  • VT
  • VF
• Key cognitive points are: 
  • Is shock present?
  • Is it a wide or narrow complex rhythm?

ECG interpretation

• Determine heart rate
• Wide or narrow
  • QRS > 0.10 at rates above 200 defines this (see table)
• Can you identify P waves and what is the relationship with each QRS
• Sinus rhythm vs. SVT
  • If looks sick, variable HR, rate <220 and normal P wave axis, sinus tachycardia is more likely
  • Fixed HR >220 in relatively well-appearing child is more likely SVT

Tachyarrhythmia needs exclusion if infant has HR >220, toddler >180 or school-age >160

Cardiac monitors are not accurate above 200

>0.10 at rate above 200 = Wide

Wide complex tachycardia

• DDx
  • VT until proven otherwise
  • SVT with aberrancy is far less common in children
  • WPW with antidromic tachycardia (down accessory and up AV node)
  • Atrial tachycardia
  • Mahaim fibre tachycardia (LBBB, left axis)
• Approach
  • Consider underlying cause i.e. congenital cardiac disease, electrolyte disturbance, medications and poisoning) and consult early
  • Synchronised DC cardioversion 1J/kg then 2J/kg if required if unstable
  • If stable: IV amiodarone or IV lignocaine (second-line)
• Fascicular VT 
  • RBBB with superior axis
  • Verapamil-sensitive and may not respond to amiodarone
  • Verapamil use in young children is VERY dangerous and must have Cardiology approval

Ventricular tachycardia

• Uncommon in children but can present as syncope, poor feeding or heart failure
• Rate is 120-300
• QRS is usualy >0.08s
• SVT with aberrant conduction is rare in children and thus most wide-complex tachycardia in children are VT
• Predisposing conditions: Congenital heart disease, ischaemia, mitral valve prolapse, myocarditis, cardiomyopathy, congenital long QT, blunt chest trauma (commotio cordis), hypokalaemia, hypomagnesaemia and drug toxicity (digoxin, cocaine, TCA)
• Rx – Synchronised DC cardioversion 4J/kg
• Lignocaine or amiodarone if refractory and to prevent recurrence

Narrow complex tachycardia

• SVT
  • 1/250 to 1/1000
  • 90% of cases due to re-entrant rhythm
  • 30-40% present in first weeks of life
    • Can be very subtle in these early stages until compromised
  • Sudden death from SVT is exceedingly rare
  • Treatment
    • Vagal manoeuvres are first-line
      • Neonates/infants: Facial immersion in ice water for 5 sec
      • Toddlers: Ice cold face cloth
      • School-age: Valsalva. Blow on thumb for 10-15sec
    • IV adenosine: 100mcg/kg, 200mcg/kg, 300mcg/kg
    • IV amiodarone if post-operative or ventricular function compromised (especially useful if actually atrial flutter or WPW circuit)
    • Synchronised DC cardioversion 1J/kg or 2J/kg if second required
    • AVOID verapamil as causes shock and cardiac arrest in infants
  • Ongoing care
    • WPW: Accounts for 25% of SVT in children. Have a tendency to AF with rapid AV conduction predisposing them to VT and sudden death. 1% risk per ten years. 
    • Should not be given digoxin (or theoretically any AV nodal blockers) and require EP studies +- ablation
  • Infants
    • 55% recurrence rate but 93% stop by age of 8-10 months
    • Infants are more likely to suffer compromise and warrant prophylactic atenolol, flecainide or sotalol
  • School-age:
    • More of a nuisance than danger and routine prophylaxis is not recommended
    • Underlying congenital heart disease rates can be as high as 20%
  • Admit all patients under 3mo and monitor rest for at least 90 minutes in ED
  • Recommend 24 hour review of all discharged cases
  • All children should receive Cardiology follow-up

Junctional ectopic tachycardia (JET)

• AV dissocation and ventricular rate 160-290 with narrow QRS
• Usually post-cardiac surgery
• Usually self-limited to 24-72 hours
• Can be fatal
• Management
  • Reduced beta-agonism
  • Avoid pancuronium as muscle relaxant
  • Induce hypothermia
  • Amiodarone infusion

Last Updated on November 22, 2021 by Andrew Crofton