Defibrillation strategies for refractory ventricular fibrillation
Cheskes S, Verbeek PR, Drennan IR, et al. N Engl J Med. 2022;387(21):1947-1956.
Ventricular fibrillation and ventricular tachycardia (VF/VT) cardiac arrest are considered the most treatment-responsive forms of cardiac arrest and have the highest rates of survival. However, as many as half of patients do not respond to multiple defibrillation attempts and are deemed to have refractory VF/VT. Refractory VF in patients with prehospital cardiac arrest has a very poor prognosis.
Double sequential defibrillation (DSD) refers to the use of 2 separate defibrillator machines on the same patient—usually 1 in the anterolateral position and 1 in the anteroposterior position on the right side (although the position can also be anterolateral, just next to the other set).
Vector-change (VC) defibrillation is a technique involving switching the defibrillation pads from the anterolateral to the anteroposterior position.
Findings regarding both these techniques have been largely mixed, and most have come from observational studies prone to bias. Prior pilot work by this same group has shown some benefits with DSD. Now the full results of their trial are available.
This is the Double Sequential External Defibrillation for Refractory Ventricular Fibrillation (DOSE VF) trial, which was designed to compare DSD and VC defibrillation vs standard defibrillation.
This was a three-group, cluster randomized trial with crossover every 6 months among 6 paramedic services in Ontario, Canada, enrolling adult patients with out-of-hospital cardiac arrest who remained in VF/VT after 3 shocks.
The target sample size was 930 patients, but the trial was stopped early because of staffing limitations during the COVID-19 pandemic.
All patients received 3 standard shocks with pads in the anterolateral position and medications according to protocols for advanced cardiac life support.
The median patient age was approximately 65 years, more than 80% were men, approximately two-thirds of the events were bystander witnessed, and slightly more than half the patients received bystander CPR.
Of the 405 patients still in VT/VF, 125 were randomized to the DSD arm, in which a second machine was used with pads in the anteroposterior position, which was activated 1 second after the first machine delivered its shock; 144 were randomized to the VC arm, in which pads were placed only in the anteroposterior position; and 136 were randomized to receive all shocks with pads in the anterolateral position.
Protocol violations occurred at a high rate: 107 of 125 patients in the DSD arm received DSD, and 113 of 144 patients in the VC arm received a VC shock. The data are presented as intent to treat.
DSD, compared with standard care, was associated with significantly higher survival to hospital discharge (30.4% vs 13.3%, RR 2.21), termination of VF (84.0% vs 67.6%), return of spontaneous circulation (46.4% vs 26.5%), and survival with good neurologic outcome (modified Rankin Score ≤2, 27.4% vs 11.2%).
VC, compared with standard care, was associated with significantly higher survival to hospital discharge (21.7% vs 13.3%, RR 1.71) and termination of VF (79.9% vs 67.6%), and showed nonsignificant trends toward higher return of spontaneous circulation (35.4% vs 26.5%) and survival with good neurologic outcome (16.2% vs 11.2%).
This was a large well-designed, randomized trial with crossover, which decreased the risk of bias generated by higher-performing or lower-performing paramedic teams. Outcome assessors were blinded to treatment allocation.
Limitations include that the treatment size might have been overestimated because the trial was stopped approximately halfway short of its target enrollment. In addition, the paramedics were not blinded and therefore might have worked harder on patients receiving a new treatment than patients receiving more of the same treatment (time on scene is not reported but might have addressed this potential bias). Finally, the total number of patients who survived to hospital discharge (the primary outcome) was small (only 18 in the control group), and the statistical significance disappeared in an analysis according to the treatment actually received (per protocol), although the trend favoring DSD and VC remained.
Concerns have been raised regarding potential damage to the equipment with DSD (although none were reported in this trial, and shocks were spaced 1 second apart), as well as the potential cost of paramedics either carrying 2 machines or having 2 units respond to implement DSD.
EDITOR’S COMMENTARY: In this large randomized, cross-over trial, the authors report a benefit with use of both DSD and VC among patients with out-of-hospital cardiac arrest and refractory VT/VF, compared with a control group receiving only standard anterolateral pad shocks for the duration of the resuscitation. The study has some unfortunate but noteworthy limitations, including sample-size concerns, lack of blinding, and protocol violations, which force us to interpret the overall results with caution. That being said, we have to make decisions according to the evidence we have, so I would use 1 of these 2 techniques after the first 3 shocks fail. This method doesn’t seem to cause harm and may have benefit, and repeating the same thing over and over just doesn’t make sense.
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Sean R. - March 7, 2023 6:30 AM
totally agree with so much of the conversation. with regard to cost, the EMS teams would only need to spend the cost of an extra set of pads for the VC approach which if a long transport time existed and an alternative to standard defib wanted to be attempted it would not be cost/personal prohibitive.