Supraventricular tachycardia (SVT) in neonates

Full good-quality 12-lead ECG to confirm that the tachycardia is narrow complex.

Assess patient

If patient relatively stable

Perform vagal manoeuvres:

• Icepack for infants (either commercially available or place crushed ice inside two plastic bags) apply icepack to face be careful of eyes and do not hold on face too long as ice can ‘burn’ an infant’s skin.
• Oropharyngeal suctioning or gag with spatula.
• Do not put pressure on eyeballs as this can result in retinal detachment.
• Do not use carotid sinus massage as this may compromise cerebral circulation.

If the patient is unstable

Appropriate resuscitative measures should be instituted including:

• Intubation and assisted ventilation (good treatment for CCF).
• Consideration of D/C cardioversion
• Review of blood gases, glucose, electrolytes (sodium, potassium, ionised calcium, magnesium) and lactate.

Intravenous adenosine

Issues to note about use of intravenous adenosine:

• Full resuscitation facilities must be available.
• Monitor ECG continuously throughout administration of adenosine.
• Adenosine can be given in a starting dose of 0.05 mg/kg, increasing by 0.05 mg/kg up to 0.25 mg/kg.
• Need to wait two minutes between doses and check patient’s vital signs.
• May use 0.30 mg/kg for recalcitrant cases with cardiologist approval.
• Adenosine should be given very quickly and as proximally in the intravenous set-up as possible. A three-way tap should be used so that the adenosine can be quickly flushed with normal saline. When the volume of adenosine is small it should be diluted with normal saline so that the drug has the chance to reach the body.
• If 0.25 mg/kg fails this can be repeated once if the patient is stable. 
• Save and inspect the recorded strip immediately after conversion to sinus rhythm has occurred for concealed pre-excitation, which may be revealed during the first few beats after conversion to sinus rhythm.
• After a patient has been reverted, a 12-lead ECG should be performed to look for pre-excitation and other abnormality.
• Rapid re-initiation of tachycardia is not uncommon, mostly due to premature atrial contractions stimulated by the adenosine. If this occurs it is reasonable to try adenosine again.
• Sometimes adenosine may cause a major pause or initiate atrial fibrillation.
• If the diagnosis is an atrial tachycardia this may be revealed by adenosine, which causes transient atrioventricular block and multiple P-waves will be seen in a row. Some atrial ectopic tachycardias are sensitive to adenosine so that the atrial impulse will stop.

Contraindications to adenosine

Adenosine is contraindicated in adenosine-deaminase deficiency, which is a rare form of immune deficiency.

Direct current cardioversion

Defibrillation should be considered for unstable patients after intubation and initiation of ventilation. 

Issues to note about defibrillation:

• It is best undertaken after consultation with a cardiologist unless the urgency is extreme.
• Infants require intravenous access and suitable sedation and analgesia.
• For tachycardias with a regular well-defined QRS complex the discharge should be synchronised with the QRS complex to avoid ventricular fibrillation.
• For ventricular fibrillation or polymorphic VT an unsynchronised shock is necessary otherwise the device will continuously delay the shock whilst trying to track the QRS complex.
• Connect the defibrillator ECG leads to the patient to obtain an ECG recording. Confirm QRS synchronisation (not T wave) by the on screen signal. 
• Select appropriate sized paddles, ensuring there is complete coverage of the paddle by gel or gel pads. Avoid gel on the skin as this may form a conductive bridge between the paddles. 
• The preferred position for defibrillation is the sternum paddle at the base of the heart, apex paddle at the apex/axilla. 
• If there is insufficient area, the sternum paddle may be applied to the front of the chest, while the apex paddle may be placed over the back, giving a front to back shock.
• SVTs usually require 1 joule per kg and ventricular arrhythmia 2-4 joules per kg.

Intravenous verapamil

NEVER give intravenous verapamil to infants with cases of severe bradycardia, hypotension and collapse noted.

Follow-up plan

The follow-up plan, including the prescription of maintenance medication, should be made in consultation with the cardiologist. Issues to note:

• Patients with recurrent re-initiation of tachycardia need discussion with the on-call cardiologist and may require transfer to the Royal Children’s Hospital.
• Digoxin should never be given in the presence of pre-excitation.
• The first-line maintenance medication would likely be a beta-blocker. These should be initiated in hospital for neonates and monitoring for hypoglycaemia should be performed. 
• Appropriate adjustments in dose should be made for premature neonates and therapeutic drug monitoring or monitoring of ECG parameters is performed if appropriate.
• The parents need to be taught how to take the pulse. It may be appropriate for this to be checked prior to putting the baby to sleep and the pulse can be checked if the baby is ‘off colour’.
• Cardiology follow-up is imperative if pre-excitation is present and optimal for other patients.
• Radio-frequency catheter ablation of arrhythmia substrate is usually reserved for children of school age and is rarely required in the neonate.
• Accessory pathway function disappears in 40 per cent of patients by the age of one year. If pathway conduction persists symptoms may settle in the first year only to return at seven or eight years of age ('cardiac puberty').

Clinical

• Auckland District Health Board (2010) Tachyarrhythmias in infants and children

Further reading

• Bauersfeld U. Pfammatter JP. Jaeggi E. Treatment of supraventricular tachycardias in the new millennium--drugs or radiofrequency catheter ablation? European Journal of Pediatrics. 160(1):1-9, 2001.