Double sequential defibrillation has been all the rage over the last few years in emergency medicine. If one shock isn’t enough, use two. (By that logic, I am sort of surprised that no one has moved on to triple sequential defibrillation yet, but there is still time.) There has never been great evidence for the practice, and actually some observational data suggesting it might not be helpful. (Mapp 2019; Emmerson 2017; Cheskes 2019) However, we now have the first proper randomized trial looking at the practice, and the results aren’t bad.
Cheskes S, Dorian P, Feldman M, et al. DOuble Sequential External Defibrillation for Refractory Ventricular Fibrillation: The DOSE VF Pilot Randomized Controlled Trial. Resuscitation. 2020; PMID: 32084567 [article] NCT03249948
This is a three-arm, pilot, cluster randomized trial with crossover conducted in 4 EMS services in Ontario, Canada.
The randomization was at the level of the EMS agency. The entire agency performed one technique for 6 months, and every agency crossed over to at least 1 other technique.
They included all adult patients with refractory VF arrest (but not patients with pulseless ventricular tachycardia) during a non-traumatic out of hospital cardiac arrest. Refractory was defined as having failed 3 defibrillation attempts with the pads in the standard anterior-lateral position, however they only counted shocks given by the EMS service, so some patients had received extra shocks before being enrolled. They excluded patients with trauma, DNR orders, hypothermia, suspected overdose, hanging, or drowning.
There were 2 interventions:
- Double sequential external defibrillation (2 shocks given via 2 defibrillators with pads attached in different positions). They had a single paramedic operate both machines, so there was a longer delay between the two shocks than in some previous descriptions. This was done because simultaneous shocks can damage the machines.
- Vector change defibrillation (switching pads from the anterior lateral to anterior posterior position).
Standard care (continued standard ACLS with shocks given through the same pads in the same anterior-lateral position).
They had a primary feasibility outcome of ensuring they could successfully deliver the assigned therapy to 80% of eligible patients.
Their safety outcome looked at damage to the machine, chest wall burns, and any concerns from paramedics, emergency department staff, patients, or their families.
Clinically, they looked at VF termination and ROSC to inform the sample size of the main study.
They enrolled 152 patients. They were able to demonstrate that this treatment is feasible, with 89% of patients getting their assigned therapy. 77% of patients were able to get their assigned therapy on the 4th shock (the earliest possible time). 93% had their assigned therapy by the 6th shock.
Return of spontaneous circulation was obtained in 25% of the standard care group, 39% of the vector change group, and 40% of the double sequence defibrillation group. They don’t include statistics or 95% confidence intervals.
The numbers were still higher but less impressive if you just look at who had a pulse on arrival to the ED (19% standard care, 25% vector change, and 33% double sequence).
There were no adverse events in any of the groups.
This is only a pilot study, and therefore is not designed to give us practice changing information. Although ROSC may appear to be higher in the double sequential defibrillation group, we should be very cautious interpreting those numbers without statistics. The main RCT is underway (NCT04080986) and will give us more definitive answers. That being said, this is the best evidence so far looking at a practice that is already relatively widespread, and at least appears to refute some of the observational data that the practice might be harmful.
There are a few minor issues with this study. 28% of patients received defibrillation attempts by the fire department, and these were not counted in their definition of “refractory VF”, meaning that patients got double sequential defibrillation later than they probably should have. They have fixed that definition for the main trial.
Cluster randomization makes perfect sense as a trial design, but can cause some problems. In the pilot study, the largest EMS agency did not get assigned to standard care. This meant that the standard care group had fewer patients. The largest agency might be different from the others. Being the largest, it might get the most practice, and therefore have the best results, which would skew these numbers. That being said, all of these EMS agencies are excellent in my experience.
The trial isn’t blinded, and I suppose there is some subjectivity in determining whether patients truly got a pulse back. The big issue is that ROSC isn’t really the outcome of interest. As I have discussed at length before, the best outcome for cardiac arrest research is neurologically intact survival. In fact, in the absence of an improvement in neurologically intact survival, I would probably consider ROSC a harm rather than a benefit. However, refractory VF patients have much better outcomes than other refractory cardiac arrest patients, so the surrogate is promising. The primary outcome of the main study is survival to hospital discharge, which is clearly better, but still not ideal in my opinion.
So what does this small RCT tell us? The strict conclusion is that double sequential defibrillation is feasible. It is also reassuring that there were no adverse events noted, although the numbers are obviously small. In terms of the rate of ROSC, I think we probably want to wait for the main trial to make any definitive conclusions. However, some people were concerned about the worse outcomes in the observational trials, and I think this trial clearly trumps that data. My best guess at this point is that double sequential defibrillation does increase ROSC. However, whether that translates into patient oriented benefit (survival with neurologic function) is unclear. The prognosis of these patients is good enough, and ROSC is a reasonable enough surrogate, that I will likely use double sequential defibrillation if I encounter a patient with refractory ventricular fibrillation while waiting for the results of the main DOSE VF study.
A note on personal conflict of interest: I have been soundly thrashed on the golf course by the lead author of this study. My friendship with him might make me less critical of the results, but my desire for revenge from the golf course might make me more critical. It is hard to say which way my feelings sway.
This small pilot study suggests that ROSC may be improved with double sequential defibrillation (and also with vetor change defibrillation) for patients with refractory ventricular fibrillation. It isn’t clear if this will translate into improved neurologically intact survival, but I think it is enough to support the practice while waiting for more data.
Note: unlike the EM:RAP video, they purposefully pushed the buttons at different times in this study.
Cheskes S, Dorian P, Feldman M, et al. DOuble Sequential External Defibrillation for Refractory Ventricular Fibrillation: The DOSE VF Pilot Randomized Controlled Trial. Resuscitation. 2020; [pubmed]
Cheskes S, Wudwud A, Turner L, et al. The impact of double sequential external defibrillation on termination of refractory ventricular fibrillation during out-of-hospital cardiac arrest. Resuscitation. 2019; 139:275-281. [pubmed]
Emmerson AC, Whitbread M, Fothergill RT. Double sequential defibrillation therapy for out-of-hospital cardiac arrests: The London experience. Resuscitation. 2017; 117:97-101. [pubmed]
Mapp JG, Hans AJ, Darrington AM, et al. Prehospital Double Sequential Defibrillation: A Matched Case-Control Study. Academic emergency medicine : official journal of the Society for Academic Emergency Medicine. 2019; 26(9):994-1001. [pubmed]