Supraventricular tachycardia (SVT) is defined as an abnormally rapid heart rhythm originating above the ventricles. It usually has narrow QRS complexes (narrow complex tachycardia) but this is not always the case. Conventionally, atrial flutter and fibrillation are excluded from this group.
SVT is the most common rhythm disturbance seen in children. Most general practitioners will deal with a case at some point. While in most cases SVT can be considered a benign rhythm disorder, special consideration needs to be given to infants, athletes and patients with Wolff-Parkinson-White (WPW) syndrome.
Understanding what causes supraventricular tachycardia
Normal electrical circuit of the heart
- The cardiac conduction system extends from the atrial to the ventricular myocardium but the atria and ventricles are electrically insulated with the sole connection via the atrioventricular node (AVN).
- The sinoatrial node (SAN) is the normal pacemaker of the heart regularly producing impulses which are conducted via the atrial myocardium to the AVN. The AVN allows the impulse to be conducted to the ventricles but with an inherent delay. This allows the atria to empty and ventricles to fill before the impulse stimulates the ventricular myocardium. Once the impulse passes through the AVN, it spreads rapidly to the ventricular myocardium via the His-Purkinje system.
Electrical circuit in SVT
- In most cases SVT is the result of a electrical short circuit caused by the presence of an additional (accessory) electrical connection between the atrium and the ventricle. The accessory connection may lie outside or within the AVN.
- The result is the presence of two electrophysiologically distinct pathways around an insulated core allowing re-entry of the electric current - hence the term re-entrant tachycardia.
The two most common types of SVT in children are:
- Atrioventricular re-entrant tachycardia (AVRT) in which there is an additional abnormal pathway between the atrium and the ventricle completing the circuit:
- In most cases the accessory connection is concealed.
- In some cases the accessory connection is visible on the ECG and allows abnormal antegrade flow of electrical impulses. This is seen as the delta wave on the ECG and known as the WPW syndrome.
- Permanent junctional reciprocating tachycardia (PJRT). There is, again, a concealed accessory connection but it transmits impulses at a much slower rate than usual. The SVT is unusually slow (130 to 150 bpm) and difficult to treat.
- Atrioventricular nodal re-entrant tachycardia (AVNRT) in which the entire tachycardia circuit is confined to the AVN and surrounding myocardium.
Other types of SVTs are more commonly seen in adults and covered in the separate article Supraventricular Tachycardia in Adults.
- Incidence of SVT is estimated to occur in 1 in 250 otherwise healthy children.
- About 50% of children with SVT present with the first episode in the first year of life.
- After infancy there is another surge in incidence in early childhood (6-9 years) and then in adolescence.
- In more than 90% of infants spontaneous resolution occurs by 1 year of age but upto a third have subsequent recurrence of SVT at a mean age of 8 years. Spontaneous resolution is uncommon (15%) in those presenting after 1 year of age.
- The most common type of SVT in children and adolescents is AVRT, with the relative proportion of patients with AVNRT increasing with age.
- Most children with SVT have a structurally normal heart but the prevalence of congenital heart disease in patients with SVT is substantially higher than that of the general population (9-32%). The most recognised association is between WPW syndrome and Ebstein's anomaly.
- Clinical presentation depends on the age of the child and the duration of SVT.
- In infants the heart rate is usually about 220 to 320 bpm and symptoms are usually nonspecific, including poor feeding, irritability, vomiting and dusky episodes. If the symptoms are unrecognised for hours or days the infant may present with heart failure or shock.
- In older children the heart rate is between 160 to 280 bpm and the usual presenting symptoms are palpitations, chest pain and shortness of breath. Often light-headedness and dizziness can occur; however, syncope is rare.
- The frequency and duration of episodes can vary hugely, with episodes lasting a few minutes to several hours and occurring once a year to several times a day.
- Physical examination is normal apart from the infant presenting in heart failure and shock.
- Diagnosis is confirmed by making an ECG recording during symptoms. Options available for this are:
- Holter (24-hour ambulatory ECG) monitoring in children having daily symptoms.
- Cardiac event recorders in those who have brief infrequent symptoms.
- ECG in the emergency department (ED) in those with infrequent but prolonged symptoms allowing them to travel to ED in the event of symptoms.
- ECG done during episodes is diagnostic and shows:
- Tachycardia with narrow QRS complexes.
- QRS complexes are regular and AV ratio is 1:1.
- P waves may not be visible as they are buried in the QRS complexes. If visible, they exhibit retrograde conduction with inverted P waves in leads II, III and aVF.
- A baseline echocardiography to confirm the presence of a structurally normally heart and to ensure that heart function is normal is recommended.
Acute management of supraventricular tachycardia
Acute management of SVT is primarily based on use of vagal manoeuvres and/or adenosine. Sometimes other medications and occasionally direct current (DC) shock are needed. Advanced Paediatric Life Support (APLS) guidelines recommend the following approach:
- Assess airway, breathing and circulation (ABC) in any child or infant presenting with SVT. Try vagal stimulation while continuing ECG monitoring. The techniques that can be used include:
- Elicit the 'diving reflex' by applying a rubber glove filled with iced water on the face or wrapping the infant in a towel and immersing the face in iced water for five seconds.
- One-sided carotid massage.
- Valsalva manoeuvre in older children.
- Give IV adenosine if vagal manoeuvres are unsuccessful. Start with a bolus dose of 100 micrograms/kg intravenously. If this does not work, increasing doses (200 micrograms/kg and then 300 micrograms/kg) can be given after two minutes. The maximum single dose that is given is 500 micrograms/kg (300 micrograms/kg in infants less than 1 month of age), up to a maximum of 12 mg.
- In a haemodynamically stable child not responding to adenosine, alternative medications should be used based on advice by a paediatric cardiologist. The options available include flecainide, amiodarone, propranolol, digoxin and procainamide. NB: verapamil has been associated with irreversible hypotension and asystole in infants and should not be used in this age group.
- Wide complex SVT (ie SVT with aberrant conduction) is uncommon in infants and children. In patients with WPW this occurs in the minority of patients who have antidromic conduction. Correct diagnosis and differentiation from ventricular tachycardia (VT) can be difficult and it is safer to treat it as VT.
- In an infant or child with SVT and in shock the best treatment option is synchronised DC cardioversion starting at a dose of 1 joule/kg and increasing to 2 joules/kg if necessary.
- Long-term management is dependent on a number of factors, including the age of patient, duration and frequency of episodes and presence of ventricular dysfunction. Management is carried out under the supervision of a paediatric cardiologist.
- In children with infrequent, mild and self-limiting episodes, usually no treatment is needed.
- In children in whom the episodes are frequent, prolonged, difficult to terminate or interfering with sports participation, treatment is indicated. Treatment options include medications or transcatheter ablation.
- The purpose of using anti-arrhythmic drugs is to slow conduction, preferentially within one limb of the re-entrant circuit and therefore terminate the tachycardia.
- Treatment options include digoxin, beta-blockers, calcium-channel blockers and the sodium-channel blocker, flecainide.
- While there is significant variation in practice, the majority of European centres use flecainide or atenolol as the first choice of drug for the prevention of recurrent SVT.
- There is little difference in the efficacy of various medications and a randomised controlled trial comparing digoxin and propranolol found no difference in recurrence of SVT in the two groups.
- While any of the anti-arrhythmics can be used to initiate treatment, in cases of WPW syndrome, use of calcium-channel blockers or digoxin should be avoided.
- Management of SVT has been revolutionised with the development of transcatheter ablation which is now considered standard treatment for older children and adolescents.
- Radiofrequency (RF) is the preferred energy source for paediatric arrhythmias and catheter ablation is only chosen if two or more anti-arrhythmic drugs have failed.
- An alternative to RF is cryoablation, which is safer and minimises the risk of heart block during ablation. However, it is associated with a higher SVT recurrence rate and therefore most centres use cryoablation in cases where RF ablation is considered a higher risk.
Sports participation and general advice
- Patients and parents should be reassured that SVT is typically not life-threatening but can be life-altering.
- Parents and patients should be taught age-appropriate vagal manoeuvres and indications for requesting assistance from emergency services. These include:
- Prolonged symptoms.
- Episode not terminated by vagal manoeuvres.
- Routine school physical activities including recreational sports participation are allowed.
- Much more caution needs to be exercised in those participating in competitive athletics and high-speed or contact sports. Guidelines issued by the American Heart Association recommend the following: -
- Asymptomatic athletes with structurally normal hearts and exercise-induced SVT prevented by medical treatment can participate in all competitive sport.
- Athletes who have had successful transcatheter ablation and are asymptomatic with no inducible arrhythmia can return to full competition.
- Symptomatic athletes with WPW syndrome have a small risk of sudden cardiac death. They should have formal electrophysiological study, risk stratification and possible ablation of their accessory pathway before participating in competitive sport.
Fetal supraventricular tachycardia
- It accounts for 60%-80% of fetal tachyarrhythmias, with prevalence ranging from 1 in 1,000 to 1 in 25,000 pregnancies.
- Clinical presentation is variable. Intermittent SVT may have no haemodynamic effect, while persistent SVT may result in fetal hydrops due to high-output cardiac failure.
- Risk of developing hydrops is related to the age of the fetus (the younger is more susceptible) and duration of SVT.
- Diagnosis is made by fetal echocardiography using M mode and Doppler.
- Treatment is transplacental therapy with anti-arrhythmics such as digoxin and flecainide.
- In the absence of structural heart disease or cardiomyopathy, the prognosis of SVT is excellent.
- WPW syndrome is associated with a small but real risk of sudden cardiac death. The main indicator of risk is the presence of symptoms. A study estimates the incidence of sudden cardiac death to be 1.1 per thousand patient years in a cohort of patients diagnosed with WPW syndrome in childhood.
- All children with an ECG diagnosis of WPW syndrome should be referred to a paediatric electrophysiologist for evaluation.
Did you find this information useful?
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