Supraventricular tachycardia (SVT) is a common arrhythmia in neonates.
SVT may initially be asymptomatic, but when prolonged it may result in congestive cardiac failure and shock after a variable period.
Other issues to note about SVT:
- SVTs are defined as those requiring tissue above the bifurcation of the bundle of His for their continuance.
- SVTs may be either atrial or atrioventricular and these groups may be further subclassified by mechanism into automatic or re-entry.
- Most SVTs in the neonate are re-entry atrioventricular SVTs utilising an accessory pathway. Most commonly the circuit of the tachycardia travels down the AV node and retrogradely up the accessory pathway. If during sinus rhythm the pathway can also conduct anterogradely (downwards) then pre-excitation can be seen on the 12-lead ECG.
- Sustained/paroxysmal SVT may develop in utero and may result in fetal hydrops.
Cardiology consultation and support
Support in the diagnosis and management of patients with SVT can be obtained initially by contacting PIPER on 1300 137 650.
Cardiology consultation regarding diagnostic and therapeutic management issues is available at any time through the switchboard of either Monash Medical Centre on (61 3) 9594 6666 or the Royal Children's Hospital on (61 3) 9345 5522.
Differential diagnosis for SVT involves:
- Sinus tachycardia at rates of up to 230 beats per minute can occur in the neonate, especially in association with fever, anaemia, sepsis and pain.
- Ventricular tachycardia in the neonate may have a relatively narrow QRS complex and must always be considered.
- SVTs other than atrio-ventricular - SVTs utilising an accessory pathway are always a possibility.
Initially investigation for SVT includes physical examination, ECG and echocardiography.
During the physical exam look for:
- general appearance
- vital signs
- presence or absence of murmur
- heart failure.
Use a 12-lead ECG to:
- help define the mechanism of the tachycardia
- later a 12-lead ECG in sinus rhythm may show pre-excitation or evidence of structural heart disease.
Points about a Holter monitor:
- It may show evidence of intermittent pre-excitation and initiating triggers such as premature atrial contractions.
- If pre-excitation is absent on the 12-lead ECG it may be appropriate to obtain this as an outpatient via a cardiologist.
An echocardiogram should be obtained after stabilisation.
There are four important structural associations of atrioventricular re-entry SVT; all may be silent to clinical examination. These are:
- Ebstein’s malformation
- congenitally corrected transposition
- dilated and hypertrophic cardiomyopathy
- myocardial tumours.
Initial management of re-entry atrioventricular tachycardia
Full good-quality 12-lead ECG to confirm that the tachycardia is narrow complex.
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.
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.
NEVER give intravenous verapamil to infants with cases of severe bradycardia, hypotension and collapse noted.
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').
- 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.
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First published: August 2013
Last web update: October 2018
Review by: March 2020
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Page last updated: 23 Nov 2018