Pediatric Tachyarrhythmia

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Rhythm Origins: Pediatric tachyarrhythmias are broadly classified by their origin and QRS width. Supraventricular Tachycardia (SVT) is the most common pediatric tachydysrhythmia. It is typically driven by an abnormal reentry circuit (e.g., AVNRT or AVRT) that bypasses the normal sinus node pacemaker.
• The Hemodynamic Cascade: While older children and adolescents may report palpitations or syncope, infants present with vague signs like irritability or poor feeding. Pediatric patients can tolerate extreme tachycardia for many hours to days due to robust cardiovascular reserves. However, at extreme rates (e.g., >220 bpm), diastolic filling time becomes severely truncated. This drastically reduces stroke volume and coronary perfusion, eventually leading to a precipitous drop into decompensated cardiopulmonary shock.
• Ventricular Tachycardia (VT): VT is fortunately uncommon in children. When present, it is often tied to underlying structural heart disease, myocarditis, toxicologic exposures, or inherited channelopathies (e.g., prolonged QT interval) that trigger early afterdepolarizations. Polymorphic VT (Torsades de Pointes) features shifting QRS polarity around the isoelectric line and is driven by severe electrolyte derangements (hypokalemia, hypomagnesemia, hypocalcemia) or QT-prolonging medications.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization: Assess airway, breathing, and circulation. Administer supplemental oxygen, attach a cardiorespiratory monitor and defibrillator pads, and establish rapid IV/IO access.
• Determine Stability: Immediately assess for cardiopulmonary compromise: acutely altered mental status, signs of shock, or hypotension.
• Stable Narrow-Complex ((\le) 0.09 sec) Management:
• Vagal Maneuvers: Attempt vagal maneuvers while preparing medications. For infants, apply a bag of ice and water to the upper face (forehead/eyes) for 15-20 seconds without occluding the airway. For older children, use unilateral carotid massage or the Valsalva maneuver.
• Adenosine: If vagal maneuvers fail, give 0.1 mg/kg (max 6 mg) as a rapid IV/IO push, delivered centrally via a 3-way stopcock, followed immediately by a rapid saline flush. If unsuccessful, repeat with 0.2 mg/kg (max 12 mg).
• Unstable Narrow-Complex ((\le) 0.09 sec) Management:
• If IV/IO access is immediately present, you may attempt a dose of Adenosine.
• Synchronized Cardioversion: Do not delay electricity for vascular access. Begin with 0.5 to 1 J/kg. If ineffective, increase to 2 J/kg. Provide sedation if time permits, but do not delay cardioversion in a crashing child.
• Wide-Complex (> 0.09 sec) Management:
• Unstable: Immediate synchronized cardioversion at 0.5-1 J/kg, increasing to 2 J/kg.
• Stable: Obtain expert consultation. Options include Amiodarone (5 mg/kg IV/IO over 30-60 min) or Procainamide (15 mg/kg IV/IO over 20-60 min).

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Top "Can't-Miss" Mimics:
• Sinus Tachycardia (ST): The ultimate mimic. Always rule out compensatory tachycardia from severe dehydration, sepsis, hypovolemia, fever, anemia, or toxic ingestions.
• Wolff-Parkinson-White (WPW) Syndrome: Can present as an orthodromic (narrow) or antidromic (wide) AV reentrant tachycardia.
• Myocarditis: A viral prodrome leading to a new tachyarrhythmia and heart failure.
• Prioritized Diagnostic Workup:
• Tier 1: A full 12-lead ECG is mandatory; a single-lead rhythm strip is insufficient for diagnosing pediatric dysrhythmias.
• Tier 2: A 20 mL/kg normal saline bolus can be a diagnostic tool. In sinus tachycardia, the rate will often gradually improve with volume loading; SVT will remain fixed.
• Tier 3: Basic metabolic panel and magnesium/calcium to rule out electrolyte-induced Torsades de Pointes.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• SVT vs. Sinus Tachycardia on ECG:
• SVT (AVNRT/AVRT): Look for an abruptly starting/stopping rhythm, absolutely regular R-R intervals with no beat-to-beat variability, and absent or abnormal P waves. The rate is exceptionally fast: typically (\ge) 220 bpm in infants and (\ge) 180 bpm in children.
• Sinus Tachycardia: Look for normal P waves preceding every QRS, variable R-R intervals (beat-to-beat variability), and a gradual warm-up/cool-down onset. Rates are usually < 220 bpm in infants and < 180 bpm in children.
• Wide Complex ECG (> 0.09 sec):
• Check for polymorphic patterns (shifting polarity and amplitude around the baseline) indicating Torsades de Pointes, or monomorphic patterns indicating standard VT or SVT with aberrancy.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• AHA PALS Pediatric Tachyarrhythmia Algorithm Checkpoints:
• QRS Duration Cutoff: Narrow is (\le) 0.09 seconds; Wide is > 0.09 seconds.
• Heart Rate Thresholds for SVT Suspicion: (\ge) 220/min in infants and (\ge) 180/min in children.
• Cardiopulmonary Compromise Criteria: Must meet one or more to be deemed "Unstable" and require electricity: acutely altered mental status, signs of shock, or hypotension.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• The Double-Drug Trap: Pitfall: Administering both Amiodarone and Procainamide for a stable, wide-complex tachycardia. Critical Action: Do not mix these agents. Giving both profoundly increases the QRS duration and QTc interval, risking lethal polymorphic VT.
• The Infant Verapamil Fatality: Pitfall: Using calcium channel blockers for SVT in infants. Critical Action: Verapamil is strictly contraindicated in children under 2 years of age because it can cause profound, irreversible myocardial depression, hypotension, and cardiac arrest.
• The Delayed Electricity Trap: Pitfall: Endlessly attempting IV access to give Adenosine to an unstable, crashing infant. Critical Action: If the child has altered mental status or shock, prepare your defibrillator pads and synchronize cardiovert (0.5-1 J/kg) immediately without delaying for an IV.
• The Poor Flush Fail: Pitfall: Injecting Adenosine into a distal peripheral IV without a rapid flush. Critical Action: Adenosine has an ultra-short half-life; it must be administered centrally or proximally via a 3-way stopcock, followed immediately by a rapid saline flush.

7. MCQ MASTERCLASS (Written Exam Tips)

• Buzzwords: "Abrupt onset," "Heart rate 240 bpm without variability," and "Absent P waves." Diagnosis: Supraventricular Tachycardia (SVT).
• High-Yield Fact: SVT is the most common tachydysrhythmia in pediatrics.
• Common Distractor: A 6-month-old presents with a heart rate of 190 bpm, fever of 39°C, normal P waves, and a 3-second capillary refill. An option suggests "Administer Adenosine 0.1 mg/kg." Differentiate: This is Sinus Tachycardia (rate <220, fever, P waves present). The correct answer is volume resuscitation (20 mL/kg NS bolus) and treating the underlying cause.
• Common Distractor: A question asks for the proper electrical intervention for an unstable 4-year-old with a narrow complex tachycardia at 210 bpm. An option will suggest "Defibrillate at 2 J/kg." Differentiate: The patient has a pulse. You must Synchronized Cardiovert starting at 0.5-1 J/kg. Unsynchronized defibrillation is reserved for pulseless arrest (VF/pVT).

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• The Opening Salvo: "This patient is presenting with a tachyarrhythmia. My immediate priorities are to assess the ABCs, apply a cardiorespiratory monitor and defibrillator pads, obtain a 12-lead ECG, and evaluate the child for signs of cardiopulmonary compromise—specifically looking at their mental status, perfusion, and blood pressure."
• Articulating the Resuscitation (Unstable): "Because the infant is lethargic, hypotensive, and the ECG shows a narrow complex rhythm at 250 beats per minute with no P waves, this is unstable SVT. I will not delay for IV access. I am ordering immediate synchronized cardioversion starting at 0.5 Joules per kilogram. I will sedate if time permits, but I will shock now."
• Articulating the Resuscitation (Stable): "The child is alert with normal perfusion and a narrow complex tachycardia of 190. I will attempt vagal maneuvers by having the child blow into a syringe like a balloon (Valsalva). If this fails, I want a proximal IV established and will administer Adenosine 0.1 milligrams per kilogram via a rapid push on a 3-way stopcock, followed instantly by a rapid saline flush."