Automated External Defibrillators, otherwise known as AED’s, have saved thousands of lives since making advanced medical technology available to non-medical professionals. The innovative, lightweight machines can restore a normal heartbeat during sudden cardiac arrest using an electric shock to the heart, and allowed a dramatic increase in cardiac saves after being placed in schools, organizations, businesses, and places of public transit.
However, improvements in AED technology continue to be made and in recent years biphasic defibrillation waveforms have become popular among manufacturers and may provide an increased probability of cardiac correction. Essentially, biphasic truncated exponential (BTE) waveforms were developed for implantable defibrillators: they used lower energies and could allow smaller, lighter devices. Manufacturer’s of AED’s, seeking ways to produce smaller, lighter, and more portable units, began incorporating this waveform over a decade ago.
Traditionally, commercial defibrillators employed either monophasic damped sine (MDS) or monophasic truncated exponential (MTE) waveforms with a limited energy setting up to 360 joules because of concern for causing myocardial damage at higher levels. With MDS waveforms, defibrillation efficacy increase as current increases, which means that for machines using the MDS waveforms, escalating energy may be needed.
Biphasic (BTE) waveforms, in contrast, have a steeper slope and their efficacy is hardly affected by an increase in current beyond a certain level. In other words, a single, fixed energy may able to be used with BTE waveforms that will effectively and safely defibrillate any patient.
Initially, early external biphasic research found that how the energy is delivered, or the shape of the electric wave, was more important than the amount of energy delivered, as long as the energy level used was high enough to defibrillate the patient without causing cardiac dysfunction. Biphasic AED’s can also adjust the waveform based on the patient’s impedance, which also increases effectiveness.
In regards to the debate over a superior waveform, the American Heart Association Guidelines 2005 also wrote that current, rather than energy, is the correct measurement of shock strength since “defibrillation is accomplished by the passage of sufficient current through the heart.” The European Resuscitation Council Guidelines 2005 also states that “although energy levels are selected for defibrillation, it is transmyocardial current flow that achieves defibrillation.”
AED manufacturers continue to produce machines utilizing both BTE and MDS waveforms, and both have been shown to be effective in terminating ventricular fibrillation. Randomized trials comparing fixed lower and escalating higher biphasic energy regimens in out-of-hospital cardiac arrest using AED’s, revealed efficient rates of ventricular fibrillation conversion and termination with escalating energy regimens. Similarly, numerous studies performed on biphasic waveforms have reported them to be highly effective at terminating ventricular fibrillation, the primary cause of sudden cardiac arrest. A multi-centered clinical trial with VF patients revealed a 96% first-shock efficacy, while another study showed a 100% first-shock efficacy, for low-energy biphasic waveforms.
It appears that the type of AED is not as important as its availability, so if your organization is looking to purchase an AED, find a trusted retailer, such as AED-SHOP.com (www.aed-shop.com) or Heart Safe America and get the units needed at your location to keep your people protected.