Biphasic waveforms spawn excitement, controversy
Biphasic waveforms have generated a great deal of enthusiasm in the resuscitation community, reports Rebecca L. Stark-Johnson, CRNA, APNP, anesthesia manager at Fort Atkinson (WI) Memorial Health Services and a regional faculty instructor for the Dallas-based American Heart Association (AHA)’s Advanced Cardiac Life Support Program. "There is a tremendous amount of controversy about this tool, much of it driven by competitive market forces," she says.
Modern defibrillators, including automated external defibrillators, deliver energy or current in waveforms, says Stark-Johnson. "Biphasic waveforms have recently been developed and approved for marketing and clinical use," she adds.
The body of evidence about the efficacy and safety of devices using biphasic waveforms has increased dramatically in the four years since the first such devices were marketed, says Stark-Johnson.
"The first biphasic automated external defibrillators approved for use in the U.S. used a waveform set at a lower energy [150 to 175 J] than that recommended by the AHA [200 J] for the first monophasic shock," she explains.
No recommendation for energies
It was also a fixed, nonescalating device, which means the energy level of the shock could not be increased, says Stark-Johnson. "The AHA has taken the stance that the optimal energies for biphasic defibrillation have not been determined," she notes. "Nor do they state the biphasic first-shock energy level yielding the highest termination rate for ventricular fibrillation."
The guidelines indicate that they cannot make a definitive recommendation for the energy for first and subsequent nonescalating biphasic defibrillation attempts, says Stark-Johnson. "Current research confirms that biphasic shocks energies of less than or equal to 200 J are safe and effective."
While both type of defibrillators are commercially available, the guidelines state that there is insufficient data to recommend one approach over another, Stark-Johnson says. "However, it is reiterated numerous times that the most important determinant of survival in adult ventricular fibrillation is rapid defibrillation," she notes.
The guidelines recommend new training requirements for automated external defibrillators. Health care providers with a duty to perform cardiopulmonary resuscitation (CPR) need to be trained, equipped, and authorized to use automated external defibrillators, says Stark-Johnson.
"Hospitals need to establish a comprehensive program for in-hospital early CPR and defibrillation," she recommends. "Those staff members trained in CPR need to be capable of providing early defibrillation."
It is now recommended that public access defibrillation be available, particularly when there might be an emergency medical services delay of five minutes or more, says Bradley. "Additionally, defibrillation in the inpatient setting should occur within three minutes."
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