Svt management paediatric dosage of drugs according to weight

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Paediatric SVT Management & Weight-Based Drug Dosing

Definition & Recognition

Feature	Sinus Tachycardia	SVT
P waves	Present	Absent or retrograde
Rate (infants)	Usually <220 bpm	Usually >220 bpm
Rate (children)	Usually <180 bpm	Usually >180 bpm
Beat-to-beat variability	Yes	No (constant R-R intervals)
Precipitating event	Fever, pain, dehydration	None

Most paediatric SVT is AVRT (AV re-entrant tachycardia) using an accessory pathway — Wolff-Parkinson-White is present in 10–20%. Narrow QRS complex is typical (orthodromic); wide QRS occurs in antidromic SVT or pre-existing bundle branch block.

Step-by-Step Management Algorithm

UNSTABLE (altered mental status, poor perfusion, hypotension, pallor, cyanosis)

→ Immediate Synchronised Cardioversion

Attempt	Energy
1st	0.5–1 J/kg
2nd	1–2 J/kg

Sedate if time permits; do not delay cardioversion for sedation in a critically unstable child.

STABLE (adequate perfusion)

Step 1 — Vagal Maneuvers (attempt first in all stable patients)

Ice pack to face (infants): Bag/glove filled with ice-water slurry applied to forehead, eyes, bridge of nose for 10–15 seconds (do not occlude nose/mouth). Most effective in infants.
Valsalva maneuver (older children): Exhale forcefully against closed glottis for 10–15 seconds in supine position.
Modified Valsalva: Standard Valsalva at 45° → immediately supine + passive leg raise at 45° for 15 seconds. Higher success than standard Valsalva.
Carotid sinus massage: Avoid in infants; not recommended in children.
Blowing into a syringe: Effective vagal maneuver in children.

Step 2 — Adenosine (if vagal maneuvers fail)

Must be given as rapid IV bolus followed immediately by a rapid NS flush (use the most proximal vein available — antecubital or central).

Dose	mg/kg	Maximum
1st dose	0.1 mg/kg	6 mg
2nd dose (if 1st fails)	0.2 mg/kg	12 mg
3rd dose (repeat 2nd if needed)	0.2 mg/kg	12 mg

Half-life ~10 seconds — flush rapidly and document rhythm strip throughout.
May cause transient wide-complex tachycardia (antidromic conduction via accessory pathway) — usually self-terminating; observe closely.
If adenosine fails → elective synchronised cardioversion under procedural sedation.

Step 3 — Amiodarone (adenosine-refractory or recurrent SVT)

Dose	Route	Notes
5 mg/kg loading dose	IV over 20–60 min	Consult paediatric cardiologist

Other Rhythm-Specific Dosing

Atrial Flutter / Atrial Fibrillation (rare in children)

Unstable: Synchronised cardioversion (0.5–1 J/kg, up to 2 J/kg)
Stable, rate control: Diltiazem, beta-blockers, or digoxin (slow ventricular response first)
⚠️ WPW + AF/flutter: Avoid adenosine, amiodarone, beta-blockers, calcium channel blockers, digoxin (the "A-B-C-D" drugs) — these block the AV node and may allow rapid accessory pathway conduction → VF. Use procainamide or cardioversion instead.

Torsades de Pointes (polymorphic VT with long QT)

Drug	Dose	Route
Magnesium sulfate	25–50 mg/kg (max 2 g)	IV over 2 minutes

⚠️ Procainamide and amiodarone are contraindicated in TdP (prolong QT further).

SVT in Post-Cardiac Surgery Children

SVT is common after atriotomy procedures (Fontan, Senning, Mustard, ASD repair). Management is the same:

Stable: Adenosine 0.1 mg/kg IV rapid bolus (max 12 mg)
Unstable: Synchronised cardioversion 0.5–1 J/kg (up to 2 J/kg)

Quick Reference Summary

Drug	1st dose (mg/kg)	Max 1st dose	2nd dose (mg/kg)	Max 2nd dose
Adenosine	0.1 mg/kg	6 mg	0.2 mg/kg	12 mg
Amiodarone	5 mg/kg IV	—	—	—
Magnesium (TdP)	25–50 mg/kg	2 g	—	—
Cardioversion (SVT)	0.5–1 J/kg	—	1–2 J/kg	—

Sources: Rosen's Emergency Medicine, 9th ed. — p.3214–3215; Tintinalli's Emergency Medicine, 9th ed. — p.870; The Harriet Lane Handbook, 23rd ed. — p.234

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