Cardiac Arrhythmias in Children: Recognition and Management

Supraventricular tachycardia (SVT) is the most common cardiac arrhythmia requiring treatment in childhood. While bradyarrhythmias in children are almost always secondary – caused by hypoxia or hypothermia, for example – SVT represents a primary cardiac disorder that can rapidly lead to hemodynamic instability without adequate treatment. In infants, the diagnosis is particularly tricky: although the heart rate may be alarmingly high at over 220/min, the clinical presentation often initially resembles sepsis or dehydration. If you can reliably recognize SVT, correctly perform vagal maneuvers, and master adenosine dosing, you can effectively manage a potentially life-threatening situation. This article systematically guides you through recognition, differential diagnosis, and stepwise treatment – from vagal maneuvers to synchronized cardioversion.

Physiological Fundamentals and Age-Specific Normal Values

Before you can assess tachycardia in a child, you need to know the age-dependent normal values for heart rate. What would be an alarming tachycardia in an adult may still be within the normal range for a neonate.

Heart Rate Reference Values

• Neonates: 100–180/min (down to 80/min during sleep)
• Infants (1–12 months): 100–160/min
• Toddlers (1–3 years): 90–150/min
• School-age children (4–12 years): 70–120/min
• Adolescents (>12 years): 60–100/min

Sinus tachycardia as a physiological response to fever, pain, anxiety, or volume depletion is by far the most common cause of an elevated heart rate in childhood. The critical clinical challenge lies in distinguishing between sinus tachycardia and SVT – a distinction that has immediate therapeutic consequences.

Supraventricular Tachycardia in Childhood

Definition and Pathophysiology

SVT refers to any tachycardia originating above the His bundle bifurcation that is not sinus-related. In childhood, two mechanisms predominate:

• Accessory pathway (AV reentrant tachycardia, AVRT): The most common mechanism in infants and toddlers. An additional electrical connection between the atrium and ventricle enables a reentrant circuit. Wolff-Parkinson-White syndrome (WPW) is the best-known variant with a visible delta wave on the resting ECG.
• AV nodal reentrant tachycardia (AVNRT): The most common mechanism in older children and adolescents. Two functionally distinct pathways within the AV node enable a reentrant circuit.

Less commonly, ectopic atrial tachycardias, junctional ectopic tachycardias, or atrial flutter occur. Atrial fibrillation is a rarity in childhood and should always raise suspicion for structural heart disease or a channelopathy.

Clinical Presentation

Symptoms vary considerably with age:

Infants and toddlers cannot verbally communicate SVT. They frequently present with:

• Irritability, poor feeding, pallor
• Tachypnea, diaphoresis
• In prolonged SVT (>12–24 hours): signs of heart failure with hepatomegaly, edema, shock

Older children and adolescents typically report:

• Palpitations, "racing heart"
• Dizziness, chest pain
• Presyncope or syncope
• Anxiety, dyspnea

The critical insight: Infants can tolerate SVT for hours before they decompensate – but then rapidly and dramatically. An infant with "unexplained heart failure" should always raise suspicion for prolonged SVT.

Diagnostics: Sinus Tachycardia versus SVT

Distinguishing between sinus tachycardia and SVT is the most important clinical differentiation step and determines subsequent management.

Clinical Differentiation Criteria

Feature	Sinus Tachycardia	SVT
Heart rate	Infant usually <220/min, child usually <180/min	Infant often >220/min, child often >180/min
Onset	Gradual	Abrupt (on/off phenomenon)
Rate variability	Yes, changes with activity, fever, stimulation	No, rigidly fixed
P waves	Present, normal positive morphology in lead II	Absent, retrograde, or abnormally shaped
QRS complex	Narrow (<0.09 s)	Narrow (<0.09 s), rarely wide
History	Fever, pain, volume depletion, anemia	No identifiable trigger
R-R interval	Variable	Absolutely regular

ECG Diagnostics

A 12-lead ECG is the diagnostic gold standard. Pay particular attention to:

• QRS width: A narrow QRS tachycardia (<0.09 s) suggests SVT. A wide QRS tachycardia (>0.09 s) is rare in childhood but must be treated as a potentially ventricular tachycardia (VT) until proven otherwise.
• P wave morphology and position: Retrograde P waves (negative in II, III, aVF) shortly after the QRS complex suggest AVRT or AVNRT. Absent visible P waves are common in AVNRT (hidden within the QRS).
• Delta wave on resting ECG: Indicative of WPW syndrome (only recognizable in sinus rhythm).

Remember: In cases of doubt and hemodynamic instability, the distinction is academic – immediate treatment is required.

Treatment Algorithm: From Vagal Maneuvers to Cardioversion

The AHA PALS guidelines structure SVT treatment according to the child's hemodynamic status. The fundamental decision point is: Is the child hemodynamically stable or unstable?

Signs of Hemodynamic Instability

• Hypotension (age-adjusted)
• Altered mental status (somnolence, irritability)
• Signs of shock: prolonged capillary refill time (>3 s), mottled or pale skin, weak peripheral pulses
• Signs of heart failure: hepatomegaly, pulmonary edema, jugular venous distension

Step 1: Vagal Maneuvers

In hemodynamically stable SVT, vagal maneuvers are the first therapeutic step. They increase vagal tone and can interrupt the reentrant circuit at the AV node.

In infants and toddlers:

• Ice application to the face: Place a plastic bag filled with ice water or an ice pack over the entire mid-face (forehead, eyes, bridge of nose) for 15–20 seconds. This triggers the diving reflex. Caution: Do not apply for longer than 20 seconds, and do not obstruct the airway.
• Rectal stimulation is mentioned in some sources but is not recommended as a first-line maneuver.
• NO pressure on the eyeballs – risk of retinal detachment, this is an obsolete technique.

In older children and adolescents:

• Valsalva maneuver: Bearing down against a closed glottis for 15–20 seconds. Practical tip: Ask the child to blow into a blocked syringe or to imagine pushing hard as if on the toilet.
• Modified Valsalva maneuver: Immediately after bearing down, lay the patient flat and elevate the legs (45°). This maneuver has shown a higher conversion rate in the adult literature.
• Carotid sinus massage: Applicable in adolescents, not reliable or recommended in young children.

The success rate of vagal maneuvers is approximately 30–60%. Even if they do not achieve conversion, the transient slowing of ventricular conduction can be diagnostically helpful in unmasking P waves on the ECG.

Step 2: Adenosine

If vagal maneuvers are unsuccessful, adenosine is the first-line medication for hemodynamically stable SVT with a narrow QRS complex.

Dosing:

• 1st dose: 0.1 mg/kg IV (rapid bolus injection), maximum dose 6 mg
• 2nd dose: 0.2 mg/kg IV (rapid bolus injection), maximum dose 12 mg

Critical Notes on Administration:

Adenosine has a half-life of less than 10 seconds. Therefore, the administration technique is critical for success:

1. IV access: Use the largest-bore peripheral access possible, ideally in the antecubital fossa or arm (the closer to the heart, the better). Access at the foot is often insufficient.
2. Stopcock technique: Draw up adenosine in one syringe and prepare a second syringe with 5–10 ml of normal saline (0.9% NaCl). Connect both to a three-way stopcock. Inject adenosine as rapidly as possible, followed immediately by a normal saline flush (rapid-flush technique).
3. Monitoring: Continuous ECG monitoring, ideally with printout/recording. The ECG pattern at the moment of conversion is diagnostically valuable.
4. Team communication: "Adenosine ready – saline ready – ECG running – injection – flush!" Team communication must be synchronized.

Side Effects and Patient Preparation: Adenosine produces a brief but intense sensation of discomfort: flushing, chest pain, dyspnea, brief asystole (seconds). Older children and adolescents should be prepared: "You will briefly feel a very uncomfortable pressure sensation in your chest that will pass within a few seconds."

Contraindications and Special Situations:

• In known WPW with a wide QRS tachycardia (antidromic AVRT or atrial fibrillation with WPW), adenosine is potentially dangerous as it can accelerate conduction over the accessory pathway and trigger ventricular fibrillation. In this case: immediately consult pediatric cardiology or proceed with electrical cardioversion.
• In patients receiving dipyridamole or after heart transplantation, the dose should be reduced (increased sensitivity).
• In patients receiving theophylline or caffeine, a higher dose may be needed (competitive antagonism at the adenosine receptor).

Step 3: Electrical Cardioversion

Synchronized cardioversion is indicated for:

• Hemodynamically unstable SVT (primary, without prior pharmacological therapy)
• Adenosine failure in stable SVT
• Wide QRS tachycardia with instability (treat as VT until proven otherwise)

Dosing:

• 1st attempt: 0.5–1 J/kg synchronized
• 2nd attempt: 2 J/kg synchronized

Practical Procedure:

1. Sedation/analgesia if the child's condition allows (e.g., midazolam 0.1 mg/kg IV or ketamine 1–2 mg/kg IV). In impending decompensation, do not delay for sedation.
2. Activate synchronization mode on the defibrillator – verify that the sync markers are correctly positioned on the R waves.
3. Place paddles/pads in anterolateral or anteroposterior position.
4. "Attention – All clear – Shock!" – standardized safety announcement.
5. After the shock: immediate rhythm check on the monitor.

Caution: With each subsequent shock attempt, the synchronization mode must be reactivated, as many defibrillators automatically revert to asynchronous mode after a discharge.

Step 4: Additional Pharmacological Options

If adenosine and cardioversion do not achieve sustained conversion or SVT recurs, the following options should be considered – ideally in consultation with pediatric cardiology:

• Amiodarone: 5 mg/kg IV over 20–60 minutes. Broad-spectrum antiarrhythmic, also applicable for wide QRS tachycardia.
• Procainamide: 15 mg/kg IV over 30–60 minutes. Do not administer concurrently with amiodarone (QT prolongation). Limited availability in Austria.
• Verapamil: Contraindicated in children under 1 year of age (risk of refractory cardiovascular collapse). In older children, use only under the strictest indications and monitoring.

Special Case: Wide Complex Tachycardia in Children

A wide QRS tachycardia in childhood is rare but potentially life-threatening. It can be caused by:

• Ventricular tachycardia (VT)
• SVT with aberrant conduction
• Antidromic AVRT in WPW

The AHA guidelines recommend: When in doubt, treat as VT. This means:

• Hemodynamically stable: Amiodarone 5 mg/kg IV over 20–60 minutes
• Hemodynamically unstable: Synchronized cardioversion at 0.5–1 J/kg, escalation to 2 J/kg
• Pulseless VT: Defibrillation (asynchronous) at 2 J/kg, escalation to 4 J/kg

Bradycardia in Children: Don't Forget

Although SVT is the focus of this article, remember: The most common cause of significant bradycardia in childhood is hypoxia. Treatment consists primarily of ensuring adequate oxygenation and ventilation. Pharmacologically, epinephrine is the primary agent:

• Epinephrine: 0.01 mg/kg IV/IO (0.1 ml/kg of the 1:10,000 solution), repeatable every 3–5 minutes
• Atropine: 0.02 mg/kg IV (minimum dose 0.1 mg, maximum dose 0.5 mg in children), primarily for vagally mediated bradycardia

Clinical Pearls and Common Pitfalls

• Pitfall: Injecting adenosine too slowly or via a distal foot IV access → ineffective due to rapid metabolism.
• Pitfall: Immediately cardioverting a hemodynamically stable SVT instead of attempting adenosine first – unnecessary intervention and sedation risk.
• Pitfall: Treating sinus tachycardia in a febrile child with adenosine → does not address the underlying cause and can provoke transient asystole.
• Pearl: After successful conversion, obtain a 12-lead ECG in sinus rhythm – the delta wave of WPW syndrome is only visible now.
• Pearl: Record the ECG during adenosine administration. Even if conversion does not occur, the transient AV block can unmask the underlying atrial activity (e.g., atrial flutter with sawtooth pattern).
• Pearl: Inform and involve parents early. The ice application to an infant's face is particularly distressing for parents – a brief explanation beforehand reduces stress for everyone involved.

Summary of the PALS Tachycardia Algorithm

1. Identification: Tachycardia with a pulse → narrow or wide QRS? → stable or unstable?
2. Narrow QRS, stable: Vagal maneuvers → Adenosine 0.1 mg/kg (max. 6 mg) → Adenosine 0.2 mg/kg (max. 12 mg) → Cardioversion or amiodarone
3. Narrow QRS, unstable: Synchronized cardioversion 0.5–1 J/kg → 2 J/kg. Adenosine may be attempted if it does not cause delay.
4. Wide QRS, stable: Treat as VT → Amiodarone 5 mg/kg IV over 20–60 min. Pediatric cardiology consult.
5. Wide QRS, unstable: Synchronized cardioversion 0.5–1 J/kg → 2 J/kg
6. Pulseless tachycardia: Begin CPR → Defibrillation 2 J/kg → PALS cardiac arrest algorithm

Hands-On Training

Managing children with cardiac arrhythmias requires more than theoretical knowledge – correct adenosine administration using the rapid-flush technique, dose calculation under time pressure, operating the defibrillator in synchronization mode, and structured team communication all need to be practiced regularly. In the PALS (Pediatric Advanced Life Support) course by Simulation Tirol, you practice exactly these scenarios in realistic simulations: from the stable child with SVT to the decompensating infant requiring immediate cardioversion. The courses follow the AHA curriculum and give you the opportunity to internalize algorithms so they are readily accessible in a real emergency.