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Double external defibrillation (DED) is the application and administration of transthoracic electrical currents from two defibrillator devices to a single patient experiencing a single type of lethal dysrhythmia during cardiac arrest, known as refractory ventricular fibrillation (RVF).[1][2] In November of 2020, the American Heart Association guidelines changed. "The usefulness of double sequential defibrillation for refractory shockable rhythm has not been established." It is currently not recommended. This use of DED occurs after standard transthoracic electrical current from a single defibrillator have failed to terminate this lethal rhythm. Refractory ventricular fibrillation is defined as ventricular fibrillation that does not convert with three or more single defibrillation attempts.[2][3] The estimated incidence of RVF is 0.5 to 0.6 per 100000 of the population; some authors report that 10 to 25% of cardiac arrest cases could develop RVF or recurrent VF.[3][4][5] Patients who experience RVF during their cardiac arrest have a mortality of up to 97%.[6][7] Proposed Theories 1) Power Theory Studies have shown that higher energy has improved success on subsequent defibrillation.[8][9][10][11] One of the leading theories behind the success of DED is that the administration of more joules during transthoracic defibrillation allows for the conversion of all the myocytes out of RVF. This approach requires the two electrical currents from both defibrillator devices to be administered at the same time or as close together as possible and is where DED gets one of it’s more common names of “double simultaneous defibrillation” (DSiD).[12][13][14] 2) Setting Up Theory Another leading theory behind DED suggests that that the first transthoracic current lowers the defibrillation threshold, which then increases the second transthoracic current’s success at converting any remaining fibrillating myocytes.[1][15] This theory requires a deliberate pause when administering the two electrical currents to ensure they are close together but not delivered at exactly the same time, and is where DED gets its most common name of “double sequential defibrillation” (DSD). 3) Multiple Vector Theory

Another leading theory behind DED suggests that that the first transthoracic current lowers the defibrillation threshold, which then increases the second transthoracic current’s success at converting any remaining fibrillating myocytes.[1][15] This theory requires a deliberate pause when administering the two electrical currents to ensure they are close together but not delivered at exactly the same time, and is where DED gets its most common name of “double sequential defibrillation” (DSD). 3) Multiple Vector Theory Another hypothesized theory behind DED directly applies to the two proposed theories above and suggests that application of multiple defibrillator pads increases the number of vectors the electrical current can use to reach the myocardium.[1][15]

Several studies have shown that safety in a patient receiving up to 720 Joules. Furthermore, studies indicate that energy level does not require adjustment for the weight.[1][9][13][14] As mentioned previously, there is a risk of damaging one or both defibrillator devices if any of the pads are touching one another when delivering the two shocks. To reiterate, damage to a defibrillator from the administration of DED is typically not covered by the manufacturer’s warranty.

There is still much unknown regarding double external defibrillation. Future studies are required to understand better whether DSD or DSiD leads to better outcomes and whether or not increased size of the defibrillator pads, to allow more surface area for the vectors of electricity, leads to more successful defibrillation. Until then, the focus during any cardiac arrest remains early defibrillation and high-quality cardiopulmonary resuscitation. DED serves as another tool in during cardiac arrest and should be an option with other advanced life-saving therapies such as ECMO and cardiac catheterization. Administration of double defibrillation requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, and emergency medical personnel, all collaborating across disciplines to achieve optimal patient results. [Level V]