Public access defibrillation: emerging importance of automated external defibrillators as a diagnostic clinical tool

The use of public access automated external defibrillators (AEDs) has rapidly increased from 2003 to 2013 — with an 11-fold growth in Victoria — and has shown improvement in survival rates for out-of-hospital cardiac arrest.1 Prompt deployment relies on lay people to recognise a cardiac arrest, operate the device and manage basic life support.2 Lay people’s use of these devices located in public locations, as opposed to specialised health care settings, is unparalleled among medical devices. However, lay people are not involved in the clinical handover of the patient with the AED and it often remains with the private owner, who may not appreciate the importance of retrieving critical AED data. Lack of handover postresuscitation of initial rhythm and AED data has been shown to underdiagnose ventricular fibrillation (VF), as well as miss other significant rhythms such as complete heart block.3,4

AEDs use arrhythmia algorithms to analyse heart rate and QRS duration from the triggered digital recording, and are designed to have a specificity of 99% and a sensitivity of > 90% for detection of VF and of > 75% for rapid ventricular tachycardia (VT), without a specific cut-off rate defined. Of four commercially available AEDs, one study indicated a large divergence in how they managed VT and supraventricular tachycardia (SVT), with some devices even delivering a shock for narrow complex SVT, therefore leading to difficulty for clinicians in interpreting the significance of an AED delivered shock.5

Specific equipment operated by trained personnel is required to download the rhythm data from the AED.2 Standardised data transmission software, either via smartphone or cellular networks, to a central server or at the hospital may fill this current critical data void. Systematic capture and documentation of the initial AED rhythm analysis may incorporate the AED as an essential diagnostic clinical tool and may reduce critical diagnostic errors and unnecessary use of implantable cardioverter defibrillators. Rhythm documentation of AED data has significant implications in determining underlying cardiac disease, dictating management and influencing preventive measures to reduce the risk of malignant arrhythmia recurrence. With the rapid expansion and increasing access of AEDs in the public domain, collaborative review of current protocols and coordination between health services, emergency management services and owners of public AEDs are required to avoid further loss of crucial data.