# Arrhythmias in Children > Arrhythmias in children for NEET-PG Paediatrics: SVT adenosine dose, WPW, congenital heart block, long QT and arrest energies in exam notes. - Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/arrhythmias-in-children - Exam / course: NEET-PG · Subject: Paediatrics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Arrhythmias in Children", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/arrhythmias-in-children ## Direct answer Supraventricular tachycardia is the commonest symptomatic tachyarrhythmia of childhood: a narrow-complex, regular tachycardia at 220-300 in infants and above about 180 in older children, usually re-entrant, terminated by vagal manoeuvres or adenosine at 0.1 mg/kg rapid intravenous push (maximum first dose 6 mg), repeated at 0.2 mg/kg (maximum 12 mg) if needed. The other pillars are congenital complete heart block, linked to maternal anti-Ro and anti-La antibodies with neonatal lupus, and the channelopathies, chiefly long QT syndrome, in which a corrected QT beyond roughly 460-480 milliseconds with exertional syncope demands beta-blockade and defibrillator assessment. In cardiac arrest, defibrillation for shockable rhythms starts at 2 joules/kg then 4 joules/kg, with adrenaline 0.01 mg/kg every three to five minutes. ## What you must remember - **Adenosine protocol:** 0.1 mg/kg by rapid bolus with a saline flush (first dose maximum 6 mg); if it fails, 0.2 mg/kg (maximum 12 mg); continuous ECG recording during the attempt, because the response is diagnostic, not merely therapeutic. - **Infant presentation:** infants may simply look pale and feed poorly for hours before heart failure appears — rate 220-300, narrow QRS, no variability. - **Wolff-Parkinson-White:** short PR, slurred upstroke (delta wave), wide QRS in sinus rhythm; risk of sudden death is why radiofrequency ablation is considered, and why accessory-pathway atrial fibrillation must never receive AV-node blockers alone. - **Congenital atrioventricular block:** maternal anti-Ro (SSA) and anti-La (SSB) antibodies crossing the placenta; pacing is indicated for rates persistently below about 50-55 per minute, ventricular ectopy, wide-complex escape or hydrops. - **Long QT syndrome:** QTc beyond approximately 460-480 milliseconds, syncope with exertion, swimming or emotion, and torsades treated with intravenous magnesium; beta-blockers are first-line therapy. - **Arrest energies and drugs:** defibrillate ventricular fibrillation or pulseless ventricular tachycardia at 2 J/kg, then 4 J/kg; adrenaline 0.01 mg/kg (0.1 mL/kg of 1 in 10,000) every 3-5 minutes; amiodarone 5 mg/kg for refractory shockable rhythms. - **Red flags in "syncope":** exertional or supine episodes, family history of sudden death under forty, and deafness (Jervell and Lange-Nielsen) all push toward arrhythmic rather than vasovagal. ## Working through a tachycardic infant A three-month-old, previously healthy, is irritable and breathing fast with a heart rate monitor reading 290. The rhythm strip shows a regular narrow-complex tachycardia with no visible P waves. First confirm perfusion — if shocked, synchronised cardioversion at 0.5-1 J/kg is the route, not drugs. If stable, apply ice to the face for up to 15 seconds (the diving reflex) while drawing up adenosine and a saline flush through a good proximal line. Give 0.1 mg/kg as the fastest push the line allows, flush immediately, and record continuously: abrupt termination confirms re-entrant supraventricular tachycardia; a transient slowing revealing flutter waves changes the diagnosis entirely. Failure at 0.1 means 0.2 mg/kg once, and if the rhythm persists, move to an infusion of amiodarone 5 mg/kg over 20-60 minutes or propranolol/esmolol and consult cardiology, searching for the infant triggers — fever, dehydration, medication, or an unsuspected Wolff-Parkinson-White. The older child with documented pre-excitation deserves electrophysiology study and ablation, but the infant who converts cleanly usually outgrows the pathway, so ablation is deferred beyond about age four to five. ## How the examiner frames it Two patterns recur. First, the recognition stem — a wide-complex tachycardia in a child is ventricular tachycardia until proven otherwise, and treating it as supraventricular tachycardia with aberrancy, with verapamil avoided in infants altogether, is the scripted error. Second, the syncope stem with a family history of drowning or unexplained death — the expected answer is an ECG with QTc measurement, not a tilt table. The congenital block question usually carries a mother with systemic lupus erythematosus or Sjögren antibodies; the anti-Ro link and the pacing threshold (roughly 50-55 per minute in a neonate) are the scored facts. Adenosine's dose ceiling — 6 mg then 12 mg — is among the most reliably examined paediatric numbers. ## Frequently asked questions ### How is adenosine given and at what dose? As an extremely rapid intravenous bolus of 0.1 mg/kg (maximum 6 mg) followed by a saline flush, repeated once at 0.2 mg/kg (maximum 12 mg), with the ECG running throughout. ### What ECG features define Wolff-Parkinson-White syndrome? A short PR interval, a delta wave slurring the QRS upstroke and a widened QRS in sinus rhythm, indicating an accessory pathway capable of re-entrant tachycardia. ### Why is congenital complete heart block linked to maternal antibodies? Maternal anti-Ro and anti-La antibodies cross the placenta and injure fetal conduction tissue; pacing is needed if the rate falls below about 50-55 per minute. ### Which children with syncope need an ECG urgently? Any child with exertional or supine syncope, deafness, or a family history of sudden cardiac death — long QT and other channelopathies must be excluded before labelling episodes vasovagal. ### What energy is used for paediatric defibrillation? An initial 2 joules per kilogram for ventricular fibrillation or pulseless ventricular tachycardia, escalating to 4 joules per kilogram for subsequent shocks.