09. Pediatric Ventricular Arrhythmias and Wide Complex Tachycardias

Ventricular arrhythmias in children represent life-threatening emergencies requiring instant differentiation between primary ventricular electrical foci, bundle branch aberrancy, and accessory pathway pre-excitation.

Figure 9.1: Clinical 12-lead ECG of Monomorphic Ventricular Tachycardia showing wide regular QRS complexes, extreme axis deviation, and AV dissociation. Rendered with solid white background.

1. Clinical Presentation & Emergency Triage

• Hemodynamic Instability: Syncope, sudden pallor, diaphoresis, unrecordable blood pressure, metabolic acidosis, cardiogenic shock.
• Idiopathic / Benign Presentations: Asymptomatic frequent PVCs discovered on routine preschool sports examination.

2. Wide Complex Tachycardia (WCT) Differentiation

Diagnostic ECG Criteria Favoring VT over SVT with Aberrancy:

1. Atrioventricular (AV) Dissociation: Independent P waves marching through wide QRS complexes (most definitive sign).
2. Capture Beats: A normal, narrow sinus beat occurring intermittently during the wide tachycardia.
3. Fusion Beats (Dressler Beats): Intermediate morphology QRS resulting from simultaneous ventricular activation by sinus and ventricular impulses.
4. Extreme Frontal QRS Axis: "Northwest" axis ($-90^\circ \text{ to } +180^\circ$).
5. Precordial Concordance: All precordial leads ($V_1 - V_6$) exhibiting entirely positive ($R$) or entirely negative ($QS$) morphology.
6. QRS Duration: $>0.09\text{ s}$ in infants, $>0.12\text{ s}$ in older children.

3. Multimodality Diagnostic Investigations

• Serum Electrolytes & Ionized Calcium/Magnesium: Rules out acute metabolic triggers.
• High-Sensitivity Troponin & NT-proBNP: Assesses acute myocardial injury and ventricular strain.
• Transthoracic Echocardiography & Cardiac MRI: Excludes underlying structural disease (Arrhythmogenic Right Ventricular Dysplasia, Left Ventricular Non-Compaction, Myocarditis, post-operative scar).

4. Evidence-Based Resuscitation & Pharmacotherapy Protocols

• Pulseless VT / Ventricular Fibrillation (VF):
  • Immediate Defibrillation ($2\text{ J/kg}$, second shock $4\text{ J/kg}$, subsequent shocks $\ge 4\text{ J/kg}$ up to max $10\text{ J/kg}$).
  • Epinephrine ($0.01\text{ mg/kg}$ IV/IO) every $3-5\text{ minutes}$.
  • Amiodarone ($5\text{ mg/kg}$ IV/IO bolus) or Lidocaine ($1\text{ mg/kg}$).
• Unstable VT with Pulses:
  • Immediate Synchronized DC Cardioversion ($0.5-1.0\text{ J/kg}$, increase to $2\text{ J/kg}$ if refractory).
• Stable VT:
  • IV Amiodarone ($5\text{ mg/kg}$ over $20-60\text{ min}$) or IV Procainamide ($15\text{ mg/kg}$ over $30-60\text{ min}$).
  • IV Magnesium Sulfate ($25-50\text{ mg/kg}$) for Torsades de Pointes.

5. Clinical Pearls & Diagnostic Traps