Supraventricular Tachycardia

Introduction

Supraventricular tachycardia (SVT) is an arrhythmia, or abnormal heart beat. Tachycardia means the heart is beating too fast. SVT is the most common abnormal fast heart rhythm in children. It affects approximately 1 in 500 young paediatric patients. The common ages of presentation are newborn, four to six years and early teenage years. Although SVT attacks can be distressing, SVT is rarely life-threatening and is highly treatable at all ages.

Causes

The heart is a muscle with four chambers. The top two are called the atrial chambers, and the lower two are the ventricles. In a normal heart, the heartbeat starts in the top right chamber (right atrium) in an area called the sinus (or sinoatrial, SA) node. The electrical signals follow set paths from the atria to its ventricles, via the atrioventricular node (AV node) in the centre of the heart. In people with SVT, the signals can sometimes “short circuit” and make the heart beat faster. When the cause of an arrhythmia is within the atria or the AV node, it is called supraventricular tachycardia (SVT), meaning “above the ventricles fast heartbeat”. This is usually because of an extra electrical connection between atria and ventricles. It can also occur when the electrical signals from the heart’s upper chambers fire abnormally, causing a fast heartbeat.

Wolff-Parkinson-White Syndrome (WPW): WPW is a malfunction of the electrical pathways, causing the signals to get to the ventricles over an extra electrical pathway. It is present since birth. Sudden cardiac death may occur, but rare in children.

SVT in children can be associated with congenital heart conditions, such as Ebstein’s anomaly.

Signs and Symptoms

Babies don’t always show symptoms of SVT right away. Their bodies can handle a fast heart rate for a while. When they do have symptoms, they usually include:

• Trouble with feeding
• Sweating when feeding
• Breathing faster than usual, almost like panting
• Seeming lethargic, like something is off

Some children with SVT have no symptoms at all. Children who are old enough to communicate what’s wrong may have symptoms like:

• Heart palpitations, or the feeling of a very fast heartbeat. This can happen at rest or during exercise. Young children may say their heart is “beeping”.
• Chest pain (children often feel a rapid or irregular heart beat as pain) and stomach ache.
• Feeling out of breath.
• Heart thumping, sometimes pulsing in the throat.
• Feeling dizzy.
• Fainting (called syncope).

Diagnosis

• To diagnose SVT, we need to record the fast heartbeat happening (e.g. palpate the radial pulse, put an ear over the child’s chest, auscultate with a stethoscope)
• SVT can be diagnosed with a simple electrocardiogram (ECG).

Special tests / investigations available in HKCH

• Exercise ECG: for children with symptoms during exercise.
• Holter: it records the ECG continuously for a certain period of time (usually for 24 hours but can extend to a few days). It is used for children with frequent symptoms.
• Cardiac event recorders: it records the ECG when the children perceive symptoms and activate the recording device. It is used for children with brief infrequent symptoms.
• Electrophysiological study: it is rarely required but can be reserved for children for refractory symptoms of likely SVT without a documented ECG changes.

Management

Acute management

• Children and their family are taught to perform vagal manoeuvres when SVT occurs. Common vagal manoeuvres include:
• Application of ice to the forehead and bridge of the nose for 20-30 seconds in neonates and infants
• For toddlers (2-5 years old), turn them upside down
• Holding breath and bearing down (Valsalva manoeuvre)
• Immersing the face in ice-cold water (diving reflex)
• Coughing
• Blowing against a thumb without letting air out (like blowing up a balloon)
• Injection of adenosine / ATP, the medication can terminate common SVT in emergency setting
• External electric shock / direct current (DC) cardioversion: electrical shock energy is delivered to terminate the abnormal rhythm
• Make it fun, and practise before the tachycardia starts so your child will be less scared and more cooperative

Long-term management

• For children with infrequent, mild and self-limiting episodes, usually no treatment is needed.
• For children whose episodes are frequent, prolonged, difficult to terminate or are interfering with sports participation, treatment is indicated.
• Treatment options include medications or transcatheter ablation.
• Medicines (such as beta blockers) may be used to slow the heart rate. Data show they are safe and effective for children. They lower the chances of having frequent or long episodes of SVT. Sometimes, they cause side effects such as nightmares or difficulty to feed.

Special treatment options available in HKCH

Transcatheter ablation of arrhythmia is a non-surgical treatment for children who have arrhythmias. It is safe and effective. This procedure uses a small, thin tube called a catheter, placed into the heart through a blood vessel in the groin or arm to heat or freeze the tissue around the area of the arrhythmia.

With ablation, we can eliminate the electrical signals that are causing the arrhythmia. Once the signals are gone, the arrhythmia is gone.

Ablation has a high success rate in curing SVT. Only rarely are there problems with destroying the normal conduction system, resulting in heart block and the need for a pacemaker. This risk arises when the abnormal pathway is very close to the AV node, or when the SVT is due to an additional pathway in the node itself (AV nodal tachycardia).

The success rate is 87-98%, and the recurrence rate is 10-15%, depending on the location of the arrhythmia. The risk of heart block is less than 1%. Serious complications occur at a low rate (1%). The procedure takes several hours and most children can go home the next day.

Follow-up Care

• Parents would be taught ways to evaluate the heart rate when a child is suspected to have SVT.
• Parents and patients would be taught age-appropriate vagal manoeuvres and indications for requesting assistance from emergency services. These include:
• Prolonged symptoms
• Episode not terminated by vagal manoeuvres
• Syncope
• Regular outpatient visits would be arranged to assess the SVT control and / or medication titration.
• Routine school physical activities including recreational sports participation are allowed.

References and Useful Resources

• Children’s Heart Federation (UK)
• Walsh MA, Gonzalez CM, Uzun OJ, et al. Outcomes From Pediatric Ablation: A Review of 20 Years of National Data. JACC Clin Electrophysiol. 2021 Nov;7(11):1358-1365.
• Dubin AM, Jorgensen NW, Radbill AE, et al. What have we learned in the last 20 years? A comparison of a modern era pediatric and congenital catheter ablation registry to previous pediatric ablation registries. Heart Rhythm. 2019 Jan;16(1):57-63.
• Philip Saul J, Kanter RJ et al. PACES/HRS expert consensus statement on the use of catheter ablation in children and patients with congenital heart disease: Developed in partnership with the Pediatric and Congenital Electrophysiology Society (PACES) and the Heart Rhythm Society (HRS). Endorsed by the governing bodies of PACES, HRS, the American Academy of Pediatrics (AAP), the American Heart Association (AHA), and the Association for European Pediatric and Congenital Cardiology (AEPC). Heart Rhythm. 2016 Jun;13(6): e251-89.
• KT Wong, TC Yung, KS Lun, et al. Ten-year Experience of Radiofrequency Catheter Ablation of Accessory Pathways in Children and Young Adult. HK J Paediatr (New Series) 2005; 10:257-264.
• Borquez AA, Williams MR. Essentials of Paroxysmal Supraventricular Tachycardia for the Pediatrician. Pediatr Ann. 2021 Mar;50(3): e113-e120.

Acknowledgement

Principal author: Dr Kwok Sit-yee on behalf of Cardiology Team, HKCH
Initial posting: Mar 2024

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