AED for Paediatric Use, Implications in the Design of Shock Advice Algorithms

Abstract

Sudden cardiac death (SCD) is the single most important cause of death in the adult population of the industrialised world (Jacobs et al., 2004). It is estimated that SCD accounts for an average of 100 to 200 deaths per 100 000 adults over 35 years and represents 50% of all heart-related death (Myerburg, 2001). Most sudden cardiac arrests occur out of hospital, and the annual incidence of out of hospital cardiac arrest (OHCA) treated by emergency medical services in the US is 55 per 100 000 population (Myerburg, 2001). Ventricular fibrillation (VF) is the initial rhythm in 40% of cardiac arrest cases (Rea et al., 2004). Survival rates in untreated VF cardiac arrest decrease by 7 to 10% per minute (Larsen et al., 1993; Valenzuela et al., 1997), as the heart function deteriorates. Although many victims present VF or ventricular tachycardia (VT) at the time of collapse, by the time the first ECG is recorded the rhythm has deteriorated to asystole (Waalewijn et al., 2002). The estimated survival rate in all cases of OHCA is a poor 8.4%, but rises to 17.7% when the victim presents VF as initial rhythm (Rea et al., 2004). Consequently, early intervention is critical for the survival of OHCA victims. In the early 1990s, the American Heart Association (AHA) established the chain of survival metaphor to describe the sequence of actions to treat OHCA. The chain of survival consists of four links: early access, early cardiopulmonary resuscitation, early defibrillation and early advanced cardiac life support. Defibrillation is normally administered using an automated external defibrillator (AED). The AED analyses the rhythm acquired through two electrode pads and delivers an electrical shock if a lethal ventricular arrhythmia – VF or rapid VT – is detected. The shock advice algorithm (SAA) of an AED analyses the ECG to discriminate shockable from non-shockable rhythms. Given a database of classified ECG records, the performance of the SAA is evaluated in terms of the proportion of correctly identified shockable – sensitivity – and non-shockable – specificity – rhythms, which must exceed the minimum values set by the AHA (Kerber et al., 1997). SCD is 10 times less frequent in children than in adults. However, only in the US, an estimated 16 000 children die each year from sudden cardiac arrest (Sirbaugh et al., 1999). Moreover, the social and emotional impact of the death of a child is enormous because of the greater life expectancy. Paediatric cardiac arrest constitutes less than 10% of all OHCA, and cardiac arrest due to arrhythmias is also less frequent in children than in adults. VF is the initially recorded AED for Paediatric Use, Implications in the Design of Shock Advice Algorithms 13