Pediatric Cardiology • Electrophysiology • Parent Guide
SVT (Supraventricular Tachycardia)
The most common arrhythmia requiring treatment in children — alarming in the moment, but almost always manageable and in many cases curable.
📚 Moss & Adams, 10th Ed. | PACES/HRS Expert Consensus Statement on SVT (2016) | ESC Guidelines on SVT (2019)
👨⚕️ Pediatric Electrophysiology
KEY STATS
| 1 in 250 | Most common | 13 m/s | >95% |
|---|---|---|---|
| Children have SVT | Arrhythmia requiring treatment in children | Conduction speed in an accessory pathway (vs. normal AV node) | Cure rate with catheter ablation for suitable SVT |
🫀 What Is SVT?
Supraventricular tachycardia (SVT) is a rapid heart rhythm that originates above the ventricles — in the atria or the AV node. During an SVT episode, the heart suddenly races at 180–280 beats per minute in children (and even faster in infants), and then — just as suddenly — returns to normal.
This abrupt on-off quality is one of the most characteristic features of SVT: the heart is normal one moment, racing the next, and normal again when the episode terminates.
SVT is not a structural heart problem — in the majority of children, the heart is structurally completely normal. The problem is electrical — an abnormal circuit or focus that can generate rapid rhythms.
The Most Common Types of SVT in Children
1. AVNRT (AV Nodal Re-entrant Tachycardia) — Most Common in Older Children / Adolescents
The AV node (the electrical gateway between atria and ventricles) has two pathways instead of one — a fast pathway and a slow pathway. Under the right conditions, an electrical impulse gets trapped going round and round between these two pathways, creating a rapid circuit. Heart rate: 150–250 bpm. The ECG shows a narrow-complex tachycardia with P waves buried in or just after the QRS.
2. AVRT (AV Re-entrant Tachycardia) — Most Common in Infants and Young Children
There is an accessory pathway — an extra electrical connection between the atria and ventricles that bypasses the normal AV node. Impulses travel down the normal pathway and back up the accessory pathway (or vice versa), creating a rapid re-entrant circuit.
When the accessory pathway conducts in the forward direction (atria → ventricles) at rest, it shows up on the ECG as a short PR interval and a “delta wave” — this is called Wolff-Parkinson-White (WPW) syndrome.
3. Automatic/Ectopic Atrial Tachycardia — Less Common
An area of atrial tissue fires spontaneously at a fast rate, overdriving the normal sinus node. Unlike re-entrant SVT, this is not abrupt in onset and offset and tends to be incessant — it may run for long periods. Can cause tachycardia-mediated cardiomyopathy if untreated.
⚠️ WPW — The Pattern That Matters
WPW (Wolff-Parkinson-White) is the ECG pattern of an accessory pathway conducting in the forward direction. Most children with WPW have SVT — AVRT using the accessory pathway. In a small minority, the accessory pathway can conduct very rapidly during atrial fibrillation, leading to a dangerously fast ventricular response (pre-excited AF). This is the rare but serious risk associated with WPW that makes it worth identifying and treating with ablation in high-risk patients.
How Does SVT Present in Children?
SVT presentation varies dramatically with age:
| Age Group | How SVT Presents |
|---|---|
| Fetus | Detected on obstetric ultrasound as rapid fetal heart rate; may cause fetal heart failure (hydrops) if sustained |
| Newborn / Infant | Poor feeding, pallor, irritability, rapid breathing — SVT at 220–300 bpm may run for hours before detection; risk of heart failure |
| Toddler / Young child | Describes feeling “heart beating fast”; may be distressed; may present only as pallor and fatigue |
| Older child / Teenager | Palpitations — sudden awareness of rapid heartbeat; may have chest discomfort, dizziness, presyncope; rarely syncope |
In infants especially, SVT can run for many hours without being detected — the baby seems generally unwell, and SVT is found on an ECG. This is why any infant who is persistently pale, feeding poorly, and tachycardic needs an ECG urgently.
🔧 Terminating an SVT Episode
Vagal Manoeuvres (First Line — No Medication)
These manoeuvres stimulate the vagus nerve, which slows conduction through the AV node and can break the re-entrant circuit:
| Manoeuvre | How to Do It | Age Group |
|---|---|---|
| Valsalva manoeuvre | Bearing down as if straining; blowing hard against a closed mouth for 15 seconds | Older children / adolescents |
| Modified Valsalva | Blow into a syringe to move the plunger, then immediately lie flat with legs raised | Teenagers |
| Carotid sinus massage | Firm massage on one side of the neck — done by a doctor | Any age (doctor-performed) |
| Ice to the face (diving reflex) | Bag of ice water applied to face for 15–30 seconds | Infants and young children |
| Ice water to drink | Quickly drinking a cup of ice-cold water | Older children |
Success rate of vagal manoeuvres: approximately 25–50%. Always attempt first if child is haemodynamically stable.
Adenosine (IV — Hospital Setting)
The drug of choice for terminating SVT acutely. Adenosine transiently blocks AV node conduction, breaking the re-entrant circuit. Given as a rapid IV push, it terminates most SVTs within 30 seconds. The dose is weight-based (0.1 mg/kg, up to 0.3 mg/kg). It causes a brief sensation of flushing, chest tightness, or “doom” — warn the child and family beforehand. The effect lasts only 10–30 seconds.
DC Cardioversion (Emergency)
For haemodynamically unstable SVT (very low blood pressure, signs of shock) — synchronised DC cardioversion under sedation terminates the arrhythmia immediately. Rarely needed for SVT but essential to know as the fallback.
Long-Term Management
| Approach | Who It Suits |
|---|---|
| No treatment (“pill in the pocket”) | Infrequent episodes, easy vagal termination, older child who tolerates SVT well |
| Daily prophylactic medication | Frequent or symptomatic episodes not controlled by vagal manoeuvres. Options: beta-blockers (propranolol, atenolol), flecainide, sotalol |
| Catheter ablation | Recurrent SVT despite medication, or patient preference for cure. Applicable from ~15–20 kg; success rate >95% for AVNRT and AVRT |
Catheter Ablation — The Curative Option
Catheter ablation is a procedure where a thin catheter is passed through a vein into the heart. An electrophysiology study maps the abnormal circuit precisely. The critical point of the circuit — the accessory pathway or the slow pathway of the AV node — is then eliminated using radiofrequency energy (heat) or cryotherapy (cold). The circuit is destroyed and cannot re-enter.
Success rate: >95% for AVNRT and AVRT.
Recurrence rate: ~5% for AVRT (accessory pathways can regenerate); ~1–2% for AVNRT.
Risk: Small but real — AV block requiring a pacemaker in <1% for AVNRT ablation (near the AV node); very low for AVRT depending on pathway location.
Most paediatric electrophysiologists wait until the child weighs 15–20 kg (approximately 4–6 years) before ablation, though earlier ablation is performed in infants with refractory or haemodynamically compromising SVT.
❓ Frequently Asked Questions
Q: My child’s heart rate was 220 bpm during an SVT episode — is that dangerous?
SVT at 180–250 bpm, while alarming in appearance, is usually haemodynamically tolerated in children with structurally normal hearts for short periods. The concern arises if: (1) the episode is sustained for many hours (risk of tachycardia-induced cardiomyopathy), (2) the child is an infant (less cardiac reserve), or (3) there is underlying structural heart disease. In a healthy child with a brief self-terminating episode, SVT is rarely immediately life-threatening. However, it must be evaluated — it does not self-manage.
Q: My daughter says her heart “suddenly starts racing and then stops” — is this SVT?
This is the classic description of re-entrant SVT. The abrupt onset (“suddenly racing”) and abrupt offset (“suddenly stops”) distinguish SVT from sinus tachycardia (fast heart rate from exercise, anxiety or fever, which builds and fades gradually). If she can capture it on a wearable device or Holter monitor, the ECG during the episode will confirm the diagnosis. An appointment with a paediatric electrophysiologist is appropriate.
Q: My child was told they have WPW on their ECG — should they have ablation?
This depends on several factors. All children with symptomatic WPW (episodes of SVT) and high-risk pathway features should be considered for ablation. The risk stratification of WPW involves assessing how quickly the accessory pathway can conduct during atrial fibrillation — done with an exercise test or electrophysiology study. Children with asymptomatic WPW (pattern found incidentally) are a more nuanced discussion — current guidelines support risk stratification before ablation in asymptomatic patients, rather than ablating all of them. This is a conversation for a paediatric electrophysiologist.
Q: Can SVT be triggered by exercise, stress, or caffeine?
Yes. Common SVT triggers include exercise, emotional stress, caffeine, insufficient sleep, and dehydration. Knowing triggers helps children manage episodes. However, unlike the dangerous arrhythmias (e.g., ventricular tachycardia in LQTS), exercise-triggered SVT in a structurally normal heart — while uncomfortable — is not immediately life-threatening. Sport restrictions are not routinely imposed for SVT pending ablation, though high-intensity competitive sport is discussed case-by-case with the electrophysiologist.
Q: My baby was found to have SVT in the womb — what happens next?
Fetal SVT can cause the fetal heart to beat at 220–300 bpm for extended periods. If sustained, this leads to fetal heart failure (hydrops fetalis). Treatment is given to the mother (medications that cross the placenta to the fetus — most commonly digoxin, flecainide, or sotalol). Most fetal SVTs are controlled with medication until delivery. After birth, many infants with neonatal SVT outgrow it by 12–18 months as the accessory pathway loses its ability to conduct — though it may reappear in adolescence. Close follow-up with paediatric electrophysiology is essential.
🎯 Key Takeaways
- SVT is the most common arrhythmia requiring treatment in children — most common cause is AVRT (accessory pathway) in infants and AVNRT in adolescents.
- The hallmark is abrupt onset and offset of rapid heart rate — distinguishing it from sinus tachycardia.
- In infants, SVT can present as non-specific illness (pallor, poor feeding, tachycardia) — an ECG must be done.
- First-line acute termination: vagal manoeuvres. Hospital backup: IV adenosine.
- Long-term options: prophylactic medication or catheter ablation (>95% curative for AVNRT and AVRT).
- WPW requires risk stratification — an electrophysiology study assesses the rare risk of pre-excited atrial fibrillation.
- Fetal SVT is manageable with maternal medication — most neonates with SVT outgrow it.
📚 References & Sources
Allen HD et al. Moss & Adams’ Heart Disease in Infants, Children, and Adolescents, 10th Ed. Wolters Kluwer, 2022.
Page RL et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients with SVT. JACC 2016.
Brugada J et al. 2019 ESC Guidelines on SVT. Eur Heart J 2020;41(5):655–720.
Shah MJ et al. PACES/HRS Expert Consensus Statement on Management of the Asymptomatic Young Patient with WPW. Heart Rhythm 2012.
© PedHeartIndia | www.pedheartindia.com — Educational purposes only.
A note from Dr. Sunil: This article is general educational information and is not a substitute for personal medical advice. For any concern about your child’s heart, please see a qualified doctor in person.
