Widespread introduction of automatic external defibrillators (AEDs) has resulted in improved outcome from ventricular fibrillation (VF).¹ These devices are designed to be used by people with little or no training, and their placement in strategic public areas (such as airports and casinos) has been reported favourably.² AEDs are now commonly used in pre-hospital care.

In children, the recommended first shock for VF is 2 J/kg using a monophasic defibrillator,³ but the data supporting this are scant.⁴ AEDs are designed for use in adults, and commonly deliver between 150 J and 200 J using a biphasic waveform. In younger children this could exceed the 10 J/kg that is thought to be potentially damaging to the myocardium, and as a result AEDs are not recommended in children under 8 years.⁵ Although ventricular fibrillation is less frequent in children than in adults, deciding whether or not to use an available AED on any child under 8 has been described as a “terrible dilemma”,⁶ particularly in a protocol driven clinical environment.

CASE REPORT

Our local ambulance despatch centre received an emergency call regarding a 6 year old girl (weight 20.4 kg), who had collapsed and appeared to be in cardiac arrest. Basic life support was initiated by the girl’s mother according to instructions given over the telephone. The first paramedic, a “rapid response unit”, arrived within 4 minutes. The child was apnoeic and pulseless. A Heartstream FR2 (Agilent Technologies, Palo Alto, CA, USA) automatic external biphasic defibrillator was attached to the child’s chest and the monitor showed asystole. Cardiopulmonary resuscitation (CPR) was commenced, and the child ventilated with oxygen. After one minute a rhythm change to VF was noted and the AED analysed this as a shockable rhythm. One shock of 150 Joules* was delivered, following which a rhythm change to asystole occurred. CPR was continued.

On the arrival of paramedic colleagues circulatory access was gained, the first dose of adrenaline was given, three cycles of the asystole protocol were completed, and endotracheal intubation was performed. After the third dose of adrenaline a rhythm change to VF was noted. A second shock of 150 J was delivered via the AED, again followed by asystole. One minute later a narrow complex bradycardia emerged with a palpable carotid pulse. The heart rate gradually increased and spontaneous respiratory effort occurred.

On arrival at the hospital the child had a palpable pulse of 80 beats/min, a respiratory rate of six, and reactive pupils. Assisted ventilation was continued. A 12 lead electrocardiogram showed a prolonged QT interval. She was initially admitted to our paediatric intensive care unit. Computed tomography of her brain and an electroencephalogram were unremarkable. Six days after her cardiac arrest the patient was conversing and self-caring. An implantable defibrillator was inserted on the assumption that her arrest was secondary to prolonged QT interval causing ventricular fibrillation. She has subsequently returned to school.

DISCUSSION

This is the second recorded case of successful resuscitation following defibrillation with an AED in a child younger than 8 years. Neither the previously reported 3 year old,⁷ nor our 6 year old child, had evidence of any myocardial damage, though in our case this is supported by echocardiographic evidence rather than additional cardiac enzyme analysis.

The existing monophasic 2 J/kg recommendation was deduced from a study of 71 transthoracic defibrillations performed on 27 children.⁴ Subsequent clinical experience suggests that this dose is effective, but the optimal dose is unknown.⁴ In addition, evidence is emerging to suggest that damage to the myocardium may be less with modern biphasic rather than traditional monophasic waveforms.⁸

Defibrillation is employed to depolarise the fibrillating heart, causing a temporary halt to electrical activity and providing an opportunity for a cardiac rhythm to be re-established. Use of higher energies may cause a prolonged depolarisation (asystole), and this may explain why the second shock was initially followed by apparent asystole before the emergence of a perfusing rhythm.

Current research in adult and animal defibrillation explores the analysis of both the defibrillation waveform and the transthoracic impedance, potentially enabling a shock with optimal energy, timing, and waveform to be delivered.⁹ Application of these principles is leading to development of paediatric defibrillators using lower energies. In the current absence of such equipment, however, professionals facing VF arrest in young children with an “adult” AED to hand will continue to face a “dilemma”.

Most practitioners are now familiar with the initial part of current recommendations: “set voltage AEDs should not be used in children under the age of 8 years”. Until new “child friendly” AEDs become available, we would use this case to draw attention to the additional statement that: “withholding use of an AED if no other defibrillator is available could cause harm”.¹⁰