Squiggler

Tired and cranky in the playground

The case

9-year-old boy. Tired and cranky in the playground

Previously well, with one similar brief episode last year that resolved spontaneously. No regular medicines.

On arrival

BP
92/58
RR
26
SpO2
98%
Cap refill
3 s
Heart rate
220

Stage 1 of 2

Noah is brought in by ambulance from school. He suddenly felt his chest go "fluttery" about 40 minutes ago and went pale. He is alert and talking. The bedside monitor shows the following trace.

Tracing 1 of 2 for the quiz “Tired and cranky in the playground”.
Bedside monitor, lead II, 25 mm/s Open this tracing in the studio
What is the rhythm on the monitor?

The monitor shows a regular narrow-complex tachycardia at 220 per minute with no visible P waves and no beat-to-beat variation in rate. Sinus tachycardia at this rate in a calm, compensated nine-year-old would be unusual and would show some variability. Atrial flutter with 2:1 block is plausible at this rate but no flutter waves are visible in the baseline. A QRS this narrow makes ventricular tachycardia very unlikely.

Vagal manoeuvres have failed and he remains haemodynamically stable. What is the next step?

In a stable child with SVT that has not responded to vagal manoeuvres, rapid intravenous adenosine given as a bolus with an immediate saline flush is the next step. Synchronised cardioversion is appropriate for the child who is haemodynamically compromised. Verapamil should be avoided in young children because of the risk of cardiovascular collapse, and amiodarone is not first-line for re-entrant SVT.

Stage 2 of 2

After adenosine he converts to sinus rhythm. A 12-lead ECG is registered.

Tracing 2 of 2 for the quiz “Tired and cranky in the playground”.
12-lead, 25 mm/s, 10 mm/mV Open this tracing in the studio

Observations

Heart rate
85
What does this 12-lead ECG show?

The PR interval is short at approximately 106 ms and there is a slurred initial upstroke to the QRS (a delta wave), best seen in leads II, III and aVF, with the QRS widened to around 120 ms. The T-wave inversion in the inferior and lateral leads is secondary to the abnormal ventricular activation, not a sign of ischaemia. A normal juvenile pattern does not produce a short PR with delta waves, and incomplete right bundle branch block would not shorten the PR interval.

Why was there no delta wave visible during the tachycardia?

In orthodromic atrioventricular re-entrant tachycardia (AVRT), the impulse travels antegrade down the AV node and retrograde up the accessory pathway. Because the ventricles are depolarised through the normal His-Purkinje system, the QRS is narrow and no delta wave appears. The delta wave is only present during sinus rhythm, when the pathway conducts antegrade and pre-excites the ventricle. An accessory pathway capable of sustaining AVRT at 220 per minute is not rate-limited to slow rates.

Diagnosis

Orthodromic AVRT in Wolff-Parkinson-White syndrome

The monitor trace shows a regular narrow-complex tachycardia at 220 per minute with no visible P waves, consistent with a re-entrant supraventricular tachycardia rather than sinus tachycardia or flutter. In a haemodynamically stable child, it is recommended to tryvagal manoeuvres followed by rapid intravenous adenosine with a flush, under continuous ECG recording. Synchronised cardioversion is the main treatment for unstable SVT

The post-conversion 12-lead is the diagnostic ECG. The short PR interval, delta wave and secondary repolarisation changes confirm ventricular pre-excitation. During the tachycardia the QRS was narrow because conduction travelled down the AV node and returned via the accessory pathway (orthodromic AVRT), so the ventricles were activated normally and no delta wave appeared. This child needs referral for electrophysiology assessment; catheter ablation is the usual definitive treatment. Adenosine was right for this narrow orthodromic tachycardia. If he ever presents in atrial fibrillation with broad, irregular pre-excited complexes, AV-nodal blocking agents such as adenosine and verapamil are dangerous, because they can accelerate conduction down the pathway.

References

  1. Brugada J, Blom N, Sarquella-Brugada G, et al. Pharmacological and non-pharmacological therapy for arrhythmias in the pediatric population: EHRA and AEPC-Arrhythmia Working Group joint consensus statement. Europace. 2013;15(9):1337-1382.
  2. Cohen MI, Triedman JK, Cannon BC, et al. PACES/HRS expert consensus statement on the management of the asymptomatic young patient with a Wolff-Parkinson-White (WPW, ventricular preexcitation) electrocardiographic pattern. Heart Rhythm. 2012;9(6):1006-1024.
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Discussion

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