⚡ Pediatric Electrophysiology
Arrhythmias in Children
Narrow Complex vs. Broad Complex Tachycardias — Mechanisms, Diagnosis, ECG Criteria & Evidence-Based Management
SVT: 1/250
Incidence in children
WPW: 0.1–0.3%
Population prevalence
95%
Adenosine success in AVNRT
QRS >120ms
Broad complex cutoff
📋 Contents
- Approach to Tachycardia in Children
- Narrow Complex Tachycardias (QRS <120ms)
- SVT — AVRT, AVNRT, Junctional Tachycardia
- Atrial Tachycardias (Atrial Flutter, FAT, IART)
- Broad Complex Tachycardias (QRS >120ms)
- Ventricular Tachycardia in Children
- Acute & Chronic Management
- Drug Dosing Reference
- Catheter Ablation — Outcomes Data
⚡ Initial Approach to Tachycardia in Children
The first question in any child with tachycardia: Is the patient hemodynamically stable? If not — synchronized cardioversion immediately. If stable — characterize the QRS width, regularity, and P-wave relationship before any pharmacological intervention.
🔍 Systematic ECG Analysis — 5 Steps
1
Rate: Age-appropriate tachycardia. Sinus tachycardia rarely >220 bpm in infants, >180 bpm in older children. SVT often 220–280 bpm (infants), 150–220 bpm (children).
2
QRS width: Narrow (<80ms neonates, <100ms infants, <120ms older) vs. Broad (≥120ms). Broad = aberrant conduction, pre-excitation, or ventricular origin.
3
Regularity: Regular (AVNRT, AVRT, monomorphic VT) vs. Irregular (AF, MAT, polymorphic VT).
4
P waves: Visible? Relationship to QRS? Short RP (RP < PR = AVNRT, AVRT) vs. Long RP (RP > PR = atrial tachycardia, PJRT, atypical AVNRT).
5
Response to vagal maneuvers / adenosine: Termination = AV node-dependent (AVNRT, AVRT). Slowing with continued P waves = atrial tachycardia. No response = VT.
| Feature | Sinus Tachycardia | SVT | VT |
|---|---|---|---|
| Rate (infants) | <220 bpm | 220–320 bpm | 150–300 bpm |
| Onset | Gradual | Abrupt | Abrupt |
| P waves | Positive, precede QRS | Often hidden/retrograde | Dissociated (AV dissociation) |
| QRS width | Narrow | Usually narrow | Usually broad (>120ms) |
| Variability | With activity/respiration | Fixed rate | Fixed (monomorphic) or variable |
| Vagal maneuver | Slows gradually | Terminates or no effect | No effect |
🔵 Narrow Complex Tachycardias (QRS <120ms)
Narrow complex tachycardia implies supraventricular origin with normal ventricular conduction. The AV node is a key player — understanding whether the arrhythmia is AV node-dependent or AV node-independent determines management.
| Arrhythmia | Mechanism | Rate (bpm) | P-wave RP | Frequency in Pediatrics |
|---|---|---|---|---|
| AVRT (orthodromic) | Re-entry via accessory pathway (anterograde AV node) | 200–280 (infants) | Short RP; retrograde P after QRS | Most common SVT in infants (~50%) |
| AVNRT | Re-entry within AV node (slow-fast pathway) | 150–250 | Very short RP; pseudo-R’ in V1 | Most common in older children/adolescents |
| Junctional Ectopic Tachycardia (JET) | Enhanced automaticity, AV junction | 170–400 (post-op) | AV dissociation, retrograde P | Post-cardiac surgery (3–8%) |
| Focal Atrial Tachycardia (FAT) | Focal automaticity or micro-re-entry | 130–250 | Long RP; P before QRS (abnormal axis) | ~10% of pediatric SVT |
| PJRT | Slowly-conducting retrograde AP (concealed) | 130–200 | Long RP; deep negative P in II,III,aVF | Rare; causes tachycardia-mediated CMP |
| IART / Atrial Flutter | Macro-re-entry in atrium | Atrial 250–350; ventricular variable | Sawtooth flutter waves | Post-op CHD (Fontan, Mustard) |
| Atrial Fibrillation | Multiple wavelet re-entry | Irregularly irregular | No organized P waves | Rare in children; associated with CHD/WPW |
AVRT & AVNRT — Key Differentiating Features
AVRT — Atrioventricular Re-entrant Tachycardia
WPW pattern if manifest AP | Most common SVT under age 1 year
🔑 ECG Features
- Narrow QRS, regular, 220–280 bpm (infants)
- Short RP interval (RP < PR)
- Retrograde P wave after QRS (negative in I, aVL if left AP)
- WPW in sinus rhythm: delta wave, short PR, broad QRS
- Orthodromic: anterograde via AV node → narrow QRS
- Antidromic: anterograde via AP → BROAD QRS (mimics VT!)
📊 Natural History Data
- 50% of infants with SVT: spontaneous resolution by 12–18 months
- 30% recur in later childhood (ages 8–12 years)
- WPW with short AP ERP: SCD risk ~0.1–0.2%/year
- High-risk WPW: intermittent pre-excitation loss during exercise stress test = low risk
- Ablation cure rate: 95–98% (left-sided AP)
- Ablation cure rate: 85–90% (right-sided AP; higher recurrence)
AVNRT — AV Nodal Re-entrant Tachycardia
Most common SVT in older children and adolescents | Dual AV nodal pathway physiology
🔑 ECG Features
- Rate 150–250 bpm; regular
- Very short RP (<70ms) — P “buried” in QRS
- Pseudo-R’ in V1 or pseudo-S in inferior leads
- Typically narrow unless aberrant conduction
- Typical (slow-fast): most common form
- Atypical (fast-slow): long RP → mimics AT/PJRT
📊 Outcomes
- Adenosine terminates 95% of acute episodes
- No SCD risk — AV node-dependent
- RF ablation of slow pathway: 97–98% cure rate
- AV block risk from ablation: <1% (complete) at experienced centers
- Recurrence after ablation: 5–8%
- Medical management: beta-blockers or flecainide 70–80% effective
Junctional Ectopic Tachycardia (JET)
Post-operative CHD emergency | Most common in first 24–48h after repair
🔑 ECG Features
- Narrow (usually) tachycardia, irregular rate
- Rate often 170–250 bpm (post-op); up to 400 bpm
- AV dissociation — more QRS than P waves
- Retrograde P waves may be visible
- Rate varies — helpful to distinguish from AVNRT/VT
- Post-op: VSD closure, AV canal, Fallot repair
🚨 Management Priorities
- Hypothermia: cool to 34–35°C → slows JET rate
- Optimize hemodynamics: reduce sympathetic drive
- Amiodarone IV: drug of choice (20–25 mg/kg/day)
- Atrial pacing at rate faster than JET to restore AV synchrony
- Procainamide: alternative for refractory JET
- Dexmedetomidine: reduces sympathetic tone, helpful adjunct
📊 Post-op JET Incidence Data
JET occurs in 3–8% of post-cardiac surgery patients overall; up to 15% after VSD closure and 20% after AV canal repair. Associated with prolonged ICU stay (+3 days) and increased mortality risk (2–3× in some series). Usually resolves within 48–72h. (Hoffman et al., JTCS 2002; Engle et al., Pediatr Cardiol 2008)
JET occurs in 3–8% of post-cardiac surgery patients overall; up to 15% after VSD closure and 20% after AV canal repair. Associated with prolonged ICU stay (+3 days) and increased mortality risk (2–3× in some series). Usually resolves within 48–72h. (Hoffman et al., JTCS 2002; Engle et al., Pediatr Cardiol 2008)
🌊 Atrial Tachycardias & Flutter
Intra-Atrial Re-entrant Tachycardia (IART) / Incisional Atrial Flutter
The dominant late arrhythmia in post-op CHD (Fontan, Mustard, Senning, ASD repair)
🔑 ECG Features
- Organized atrial activity; rate 150–300 bpm
- Variable AV conduction (2:1, 3:1, 4:1)
- Flutter waves may be atypical (not classic sawtooth)
- In Fontan: often 2:1 with ventricular rate 150 bpm
- Must exclude accessory pathway (WPW) — 1:1 conduction lethal
📊 Epidemiology
- Fontan patients: 30–50% incidence by 10 years post-op
- Mustard/Senning repair: 25–40% by 20 years
- ASD closure (surgical): 5–10% late AF/flutter
- IART recurrence after cardioversion: 50–70% at 1 year without ablation
- Ablation success: 70–80% (complex anatomy limits efficacy)
Focal Atrial Tachycardia (FAT)
Incessant form → tachycardia-mediated cardiomyopathy if untreated
🔑 ECG Features
- Long RP tachycardia (RP > PR)
- P waves with abnormal axis (depending on focus site)
- Warms up/cools down (automaticity)
- NOT terminated by adenosine — only slowing of ventricular rate
- Right atrial FAT: negative P in V1, positive in aVL
- Left atrial FAT: positive P in V1, negative in I
📊 Outcomes & Ablation
- Incessant FAT → CMP in 10–20% if untreated >3–6 months
- CMP usually reversible with rate control/ablation
- Ablation success: 85–90% (right atrial foci)
- Left atrial foci: 75–80% success
- Crista terminalis most common location (right atrium)
- Antiarrhythmic drugs: partially effective; ablation preferred
Broad Complex Tachycardias
🔴 Broad Complex Tachycardias (QRS >120ms)
Broad complex tachycardia in a child must be treated as ventricular tachycardia until proven otherwise. The differential includes: VT, SVT with aberrant conduction, antidromic AVRT, and SVT with pre-existing bundle branch block.
⚠️ Golden Rule
In hemodynamically unstable broad complex tachycardia → SYNCHRONISED CARDIOVERSION (0.5–2 J/kg). Do NOT waste time trying to determine the mechanism. Misdiagnosing VT as SVT and giving verapamil is potentially fatal in children. Verapamil is CONTRAINDICATED in infants with any tachycardia and in any child with broad complex tachycardia.
In hemodynamically unstable broad complex tachycardia → SYNCHRONISED CARDIOVERSION (0.5–2 J/kg). Do NOT waste time trying to determine the mechanism. Misdiagnosing VT as SVT and giving verapamil is potentially fatal in children. Verapamil is CONTRAINDICATED in infants with any tachycardia and in any child with broad complex tachycardia.
Differentiating VT from SVT with Aberrancy
| Criterion | Favors VT | Favors SVT + Aberrancy |
|---|---|---|
| AV dissociation | Present (pathognomonic for VT) | Absent (P waves track QRS) |
| Capture beats | Present (narrow QRS amid broad) | Absent |
| Fusion beats | Present (partially conducted sinus beat) | Absent |
| QRS morphology | Concordance in precordial leads | Typical LBBB or RBBB morphology |
| Brugada criteria | Rs >100ms in any precordial lead | Typical conduction pattern |
| Response to adenosine | No effect (most VT) | Terminates |
| Clinical history | Structural/CHD, channelopathy | Prior SVT, no structural disease |
| QRS axis | Northwest axis (−90° to ±180°) | Normal or right axis |
Brugada Criteria (4-step algorithm)
- Step 1: RS complex absent in all V1-V6 → VT
- Step 2: RS interval >100ms in any precordial lead → VT
- Step 3: AV dissociation present → VT
- Step 4: Morphology criteria (RBBB/LBBB pattern) not typical → VT
- All steps negative → SVT with aberrancy
- Sensitivity 99%, specificity 97% for VT (in adults)
Antidromic AVRT (WPW)
- Pre-excitation with anterograde conduction via AP
- Broad QRS (≥120ms), maximally pre-excited morphology
- Rate often very fast (200–300 bpm)
- If AF + WPW: irregular, broad, very fast >250 bpm
- AF+WPW: AVOID adenosine, digoxin, verapamil
- AF+WPW treatment: DC cardioversion, procainamide, or ibutilide
🔴 Ventricular Tachycardia in Children
Idiopathic Left Ventricular Tachycardia (ILVT / Belhassen VT)
Most common “benign” VT in children with structurally normal hearts | Responds to verapamil
🔑 ECG Features
- RBBB morphology + Left axis deviation
- Relatively narrow QRS (120–140ms)
- Origin: posterior fascicle of left bundle
- Rate 120–200 bpm; hemodynamically tolerated
- Exercise-sensitive in some cases
- Responds to verapamil IV (diagnostic and therapeutic)
📊 Outcomes
- No structural heart disease required
- No increased SCD risk in structurally normal hearts
- Verapamil IV effective in 85–95% for acute termination
- RF ablation: posterior fascicle targeting; 90–95% cure
- May recur spontaneously → often observation acceptable
- Avoid misdiagnosing as AVNRT (different morphology)
Right Ventricular Outflow Tract VT (RVOT-VT)
Catecholamine-sensitive | LBBB morphology + inferior axis | May mimic APB on Holter
🔑 ECG Features
- LBBB morphology, inferior axis (tall R in II,III,aVF)
- Origin: RVOT, septal or free wall
- Often exercise-induced or adrenergic-triggered
- May present as frequent PVCs or repetitive monomorphic VT
- Structurally normal heart (rule out ARVC)
- ARVC: LBBB-VT + RV dilation/fatty infiltration → different prognosis
📊 Management
- Beta-blockers: first-line for symptomatic RVOT-VT (70–80% effective)
- Verapamil: alternative if beta-blocker fails
- RF ablation: 85–95% cure rate; preferred for frequent/symptomatic VT
- Must exclude ARVC (cardiac MRI, family history, epsilon waves)
- Exercise stress test: VT suppressed with increasing rate (helpful feature)
VT Associated with Structural & Channelopathy Diagnoses
| Diagnosis | VT Mechanism | ECG Clue | SCD Risk | Treatment |
|---|---|---|---|---|
| ARVC | Scar-related re-entry, RV | Epsilon wave, T-inv V1-V3, LBBB-VT | High (2–3%/yr untreated) | ICD + beta-blocker; ablation for storm |
| HCM | Scar-based re-entry | LVH, dynamic LVOTO | 1–2%/yr (high-risk) | ICD for high-risk; disopyramide |
| CPVT | DAD, catecholamine-triggered | Normal resting ECG; bidirectional VT on exercise | 30–50% events without treatment | Beta-blocker + flecainide; ICD + nadolol |
| Long QT Syndrome | EAD-triggered torsades | QTc >460ms (F), >440ms (M); T-wave morphology | ~0.5%/yr untreated LQT1; higher LQT2,3 | Beta-blocker; avoid QT-prolonging drugs; ICD |
| Brugada Syndrome | Phase 2 re-entry; VF | Coved ST elevation V1-V3 (type 1) | 0.5–2%/yr; highest in males | ICD; quinidine; avoid fever/certain drugs |
| Post-op TOF | Scar-based macro-re-entry | RBBB (baseline); QRS >180ms = risk marker | 0.5–1.5%/yr long-term | ICD if high-risk; VT ablation |
🏥 Acute & Chronic Management
⚡ Acute Hemodynamically Unstable Tachycardia — Any QRS Width
1
Synchronised DC cardioversion: 0.5–1 J/kg → increase to 2 J/kg if unsuccessful. Sedate with ketamine or midazolam if time permits. Do NOT delay for IV access.
2
If VF/pulseless VT: Unsynchronised defibrillation 2 J/kg → 4 J/kg → 4 J/kg. Follow PALS algorithm (epinephrine, amiodarone).
3
Identify and treat reversible causes: Hypoxia, acidosis, hypo/hyperkalemia, hypomagnesemia, drug toxicity (QT-prolonging agents).
💊 Acute Stable SVT — Step-Up Approach
1
Vagal maneuvers: Ice water facial immersion (diving reflex) — most effective in infants. Valsalva (older children). Carotid sinus massage. 20–30% conversion rate.
2
Adenosine IV: 0.1 mg/kg rapid IV push (max 6mg first dose, 12mg subsequent). 95% effective for AV node-dependent SVT. Use large-bore IV, as close to heart as possible. Half-life 10 seconds.
3
If adenosine fails: Reassess mechanism. If truly SVT: IV beta-blocker (metoprolol 0.1 mg/kg) or IV amiodarone (5 mg/kg over 20 min). If uncertain/broad: treat as VT.
4
Synchronized cardioversion if pharmacological conversion fails and patient deteriorates: 0.5–1 J/kg.
⚠️ NEVER Give in Children
Verapamil: CONTRAINDICATED in infants <1 year (causes profound hypotension and cardiac arrest) and in broad complex tachycardia of any age (may precipitate hemodynamic collapse in VT).
Verapamil: CONTRAINDICATED in infants <1 year (causes profound hypotension and cardiac arrest) and in broad complex tachycardia of any age (may precipitate hemodynamic collapse in VT).
Digoxin in WPW: Shortens accessory pathway refractory period → may accelerate conduction and precipitate VF. Absolutely contraindicated.
💊 Drug Dosing Reference
Adenosine
Endogenous nucleoside — AV nodal blocker
0.1 mg/kg IV rapid push (max 6 mg initial dose)
Repeat: 0.2 mg/kg (max 12 mg)
Half-life: 10 seconds | Rapid large-bore IV essential
Repeat: 0.2 mg/kg (max 12 mg)
Half-life: 10 seconds | Rapid large-bore IV essential
Amiodarone
Class III — multi-channel blocker
Acute: 5 mg/kg IV over 20–60 min (max 150 mg/dose)
Infusion: 5–15 mcg/kg/min
Post-op JET: 20–25 mg/kg/day IV (divided q6–8h)
Infusion: 5–15 mcg/kg/min
Post-op JET: 20–25 mg/kg/day IV (divided q6–8h)
Flecainide
Class IC — Na-channel blocker
PO: 2–8 mg/kg/day divided q8–12h
Avoid in structural heart disease (post-CAST trial)
Excellent for CPVT (add to beta-blocker)
Avoid in structural heart disease (post-CAST trial)
Excellent for CPVT (add to beta-blocker)
Propranolol
Non-selective beta-blocker
PO: 1–4 mg/kg/day divided q6–8h (infants up to 8 mg/kg/day)
IV: 0.01–0.1 mg/kg over 10 min (max 1 mg)
First-line for LQTS, CPVT, RVOT-VT
IV: 0.01–0.1 mg/kg over 10 min (max 1 mg)
First-line for LQTS, CPVT, RVOT-VT
Sotalol
Class III + beta-blocker
PO: 2–8 mg/kg/day divided q8–12h (infants up to 16 mg/kg/day)
Monitor QTc (check 4–6h after dose change)
Reduce dose in renal impairment
Monitor QTc (check 4–6h after dose change)
Reduce dose in renal impairment
Digoxin
Cardiac glycoside — vagotonic, AV nodal slowing
Maintenance: 10 mcg/kg/day (neonates); 5–10 mcg/kg/day (infants/children)
⛔ CONTRAINDICATED if WPW present (risk of VF)
Narrow therapeutic window — monitor levels
⛔ CONTRAINDICATED if WPW present (risk of VF)
Narrow therapeutic window — monitor levels
Procainamide
Class IA — Na-channel blocker
Acute IV: 15 mg/kg over 30–60 min (max 1g) → then 20–80 mcg/kg/min
Monitor for hypotension during loading
Useful for VT, AF+WPW, post-op VT
Monitor for hypotension during loading
Useful for VT, AF+WPW, post-op VT
🎯 Catheter Ablation — Outcomes Data
Radiofrequency (RF) and cryoablation are standard curative therapies for most pediatric arrhythmias. 3D electroanatomic mapping (CARTO, EnSite) has transformed ablation of complex arrhythmias in CHD patients.
| Arrhythmia | Target | Acute Success | Recurrence | Major Complication Risk |
|---|---|---|---|---|
| AVNRT | Slow pathway | 97–98% | 5–8% | AV block <1% |
| AVRT — Left AP | Left lateral / posteroseptal AP | 95–98% | 3–5% | <0.5% |
| AVRT — Right AP | Right-sided AP | 85–92% | 10–15% | <1% |
| Atrial Flutter (typical) | Cavo-tricuspid isthmus | 95–97% | 5–10% | <1% |
| IART (post-CHD surgery) | Ablation of critical isthmus | 70–80% | 30–50% | 1–3% |
| Focal AT | Focal site (crista terminalis, etc.) | 85–90% | 10–20% | <1% |
| ILVT (Belhassen VT) | Posterior fascicle | 90–95% | 5–10% | LBBB <1% |
| RVOT-VT | RVOT focus (activation/pace-mapping) | 85–95% | 8–15% | <1% |
| CPVT-associated VT | Purkinje network (PVC trigger) | 60–75% | High | Varies |
📊 PACES/HRS Multicenter Pediatric RF Ablation Registry (n=4,651 procedures)
Overall procedural success: 91.8%. Major complications: 3.2% (including complete AV block 0.9%, cardiac perforation 0.3%, thromboembolism 0.2%). Mortality: 0.12%. Cryoablation for parahisian/septal pathways: eliminates AV block risk but 15–20% higher recurrence rate vs. RF. Under age 15kg: increased complication risk — defer elective ablation when possible. (Van Hare et al., JACC 2000; updated AHA scientific statement 2016)
Overall procedural success: 91.8%. Major complications: 3.2% (including complete AV block 0.9%, cardiac perforation 0.3%, thromboembolism 0.2%). Mortality: 0.12%. Cryoablation for parahisian/septal pathways: eliminates AV block risk but 15–20% higher recurrence rate vs. RF. Under age 15kg: increased complication risk — defer elective ablation when possible. (Van Hare et al., JACC 2000; updated AHA scientific statement 2016)
📋 PACES/HRS Age Thresholds for Ablation
Elective ablation generally deferred until age 4–5 years or weight >15 kg to minimize vascular access complications. Exceptions: (1) drug-refractory SVT causing hemodynamic compromise, (2) WPW with high-risk features (shortest pre-excited RR interval ≤250ms), (3) incessant tachycardia-mediated cardiomyopathy. Ablation earlier carries higher complication rates but may be necessary.
Elective ablation generally deferred until age 4–5 years or weight >15 kg to minimize vascular access complications. Exceptions: (1) drug-refractory SVT causing hemodynamic compromise, (2) WPW with high-risk features (shortest pre-excited RR interval ≤250ms), (3) incessant tachycardia-mediated cardiomyopathy. Ablation earlier carries higher complication rates but may be necessary.
