A PALE, BREATHLESS BABY
History
Alfie is a 7-month-old baby who is seen in the A&E department with a day’s history of pallor. Over the past few hours, he has also become restless and breathless. He is feeding poorly. He has no cough or wheeze. There is no past medical history of note and he is on no medication. His 3-year-old sister has a cold but a 5-year-old brother and the rest of the family are well.
Examination
He is apyrexial, pale and his oxygen saturation is 91 per cent in air. The heart rate is 270 beats/min, blood pressure is 84/44 mmHg, heart sounds are normal and femoral pulses are palpable. The peripheral capillary refill is 4 s. Respiratory rate is 62 breaths/min and the chest is clear. The liver is palpable 4 cm below costal margin. There are no other signs.
INVESTIGATIONS
Haemoglobin 12.8 g/dL 10.5–13.5 g/dL
White cell count 7.0 109/L 4.0–11.0 109/L
Platelets 323 109/L 150–400 109/L
Sodium 138 mmol/L 135–145 mmol/L
Potassium 3.9 mmol/L 3.5–5.0 mmol/L
Urea 6.4 mmol/L 1.8–6.4 mmol/L
Creatinine 60 µmol/L 20–80 µmol/L
C-reactive protein 5 mg/L 6 mg/L
ECG – see Figure 11.1
Questions
• What does the ECG show and what is the diagnosis?
• What treatments can be used to manage this condition?
Medicine
The ECG shows a narrow QRS complex tachycardia with a rate of approximately 220 beats/min. There are no P waves. The diagnosis is supraventricular tachycardia (SVT). This is the commonest pathological arrhythmia in childhood (sinus arrhythmia is a normal variant). Diagnosis is based on the presence of a narrow QRS complex tachycardia. P waves are only visible in about half of cases. It is usually secondary to a re-entrant tachycardia using an accessory pathway. It is also associated with the Wolff–Parkinson–White syndrome (see Fig. 11.2). This condition can be diagnosed by a short PR interval and a slow upstroke of the QRS (delta wave). These are normally only seen when the patient does not have a tachycardia.
Figure 11.2 Intermittent pre-excitation in Wolff–Parkinson–White syndrome. The first two beats show the short PR interval and delta wave. The middle two beats are normal and the abnormality returns in the final two beats. (Reproduced with permission from Worrell DA, ed, Oxford Textbook of Medicine, 2003, Oxford University Press.)
The heart rate in SVT is typically 200–300 beats/min. Arrhythmias can last from a few seconds to days. In older children, they can be associated with palpitations, light-headedness and chest discomfort. However, in young infants, the inability to report symptoms may lead to presentation with heart failure and shock, as in this case. In a third of cases there is associated congenital heart disease so an echocardiogram should be performed. Supraventricular tachycardia needs to be differentiated from sinus tachycardia. In the latter, the heart rate is usually 220 beats/min, there is greater variability in the heart rate and there is often a history consistent with shock.
Features of heart failure
• Tachycardia
• Tachypnoea
• Hepatomegaly
• Poor feeding
• Sweating
• Excessive weight gain (acutely)
• Poor weight gain (chronically)
• Gallop rhythm
• Cyanosis
• Heart murmur
Initial treatment in this emergency follows the standard resuscitation guidelines and the baby should be administered oxygen. Capillary refill is slightly prolonged but should improve swiftly following the correction of the tachycardia. Specific treatment comprises vagal stimulation, for instance by eliciting the ‘diving reflex’ which will increase vagal tone, slow atrioventricular conduction and abort the tachycardia. This can be done by placing a rubber glove filled with iced water over the baby’s face. If this fails, the baby’s face can be immersed in iced water for 5 s. Second-line treatment comprises intravenous adenosine that can be administered in escalating doses. If this fails, synchronized DC cardioversion will almost always stop the tachycardia. Once sinus rhythm is achieved, maintenance treatment using drugs such as amiodarone should be started following consultation with a cardiologist. Infants (1 year old) with SVT are less likely to relapse than older children. They are often treated for 1 year, following which the medication is slowly tapered. In the majority of cases, the SVT does not recur. Definitive treatment comprises catheterization with radiofrequency ablation.
KEY POINTS
• SVT is the commonest pathological arrhythmia in childhood.
• It can lead to heart failure and shock.
• Treatments comprise vagal manoeuvres, adenosine and DC cardioversion
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