This ECG is from a 10yr old boy who presented with mild dysponea.
Wheeze at home treated with inhaler. Past medical history of mild asthma, nil developmental concerns. Only medication is salbutamol inhaler PRN.
Vitals signs: BP 105/60 RR 20 T 36.4 Sats 99%
Check out the comments from our original post here.

Click to enlarge

Rate:

~200 bpm

Rhythm:

Regular

Axis:

Normal axis

Intervals:

QRS - Normal (600ms)
QT - 220ms (QTc Bazette415 ms)

Segments:

ST Elevation leads aVR, V1, V2
ST Depression leads II, III, aVF, V3-6

Additional:

Retrograde p waves best visible in leads aVL and V2

Pseudo-R prime & Pseudo S

Interpretation:

Narrow Complex Tachycardia in a paediatric patient.
AVNRT

The retrograde P wave in V1, V2 is too close to the QRS to be AVRT
You can not make it from ventricle to atrium over an accessory pathway so quickly you need a minimum of 70-80 msec

For more about the anatomical basis for various arrhythmias in children check out this article recommended by our electrophysiologists.

Asirvatham SJ. Cardiac Anatomic Considerations in Pediatric Electrophysiology. Indian Pacing Electrophysiol J. 2008 Apr-Jun; 8(Suppl 1): S75–S91. Pubmed Full Text.

What happened ?

A venous blood gas revealed normal electrolytes. Vagal manoeuvres were attempted but failed to revert the rhythm so we proceeded to adenosine. A 100 mcg/kg dose resulted in successful cardioversion, rhythm strip below.

Click to enlarge

I just realised I don't have a copy of the full post reversion 12-lead ECG but this did not show any evidence of pre-excitation.

Management of Paediatric SVT

90% of paediatric arrhythmias are SVT. 90% of SVTs are of re‐entrant type. Half of paediatric patients with SVT will have no underlying heart disease, a quarter will have congenital heart disease and the other quarter will have Wolf Parkinson White syndrome.

Look for potential precipitants such as fever, metabolic/electrolyte abnormalities, and drug exposure. The SVT may be well tolerated for an extended period, up to 12-24 hours before signs of cardiac failure appear.

Treatment should occur in a step-wise manner. In the uncomplicated patient vagal manoeuvres should be tried prior to chemical cardioversion, with adenosine being the preferred agent.
If chemical cardioversion with adenosine is unsuccessful paediatric cardiology advice should be sought for advice on next-line agents For complex patients early paediatric cardiology advice should be sought.

Options for vagal manoeuvres depend on patients age. For Infants you can put iced water in bag and place this on the face for up to 10 seconds. In older children you can try carotid sinus massage, valsalva , deep inspiration/cough/gag reflex, and even headstand.

Adenosine is a very short acting AV and sinus nodal blocker. It is given via a proximal IV cannula followed by / or with a saline flush. Side-effects are transient but including flushing, nausea, bronchospasm, and 'sense of doom'. It is given in an escalating dose regime:

1st dose 100 mcg/kg
2nd dose 200 mcg/kg
3rd dose 300 mcg/kg

Give doses 2 minutes apart.
Maximum single dose 12mg

Do NOT use verapamil or beta blockers in infants or children with SVT – cause profound AV block, negative inotropy and sudden death.

The shocked / compromised child with SVT will require DC cardioversion. Be very wary of cardioverting an ‘unstable’ child in a SVT who requires sedation or anaesthesia as rapid deterioration of the ‘SVT‐stressed’ myocardium may occur with anaesthesia with resultant death.

References / Further Reading

Life in the Fast Lane

Textbook