Date: February 7, 2023

Reference: Cheskes et al. Defibrillation Strategies for Refractory Ventricular Fibrillation. NEJM 2022

Guest Skeptic: Dr. Sean Moore is an emergency physician working in Kenora Ontario, where he is Chief of Staff at Lake of the Woods District Hospital, Northern Medical Director for the Ornge air medical transport program and associate medical director with CritiCall Ontario.  Research interests include simulation-based assessment, transport medicine, and critical care analgesia.   He is an assistant professor at the Northern Ontario School of Medicine University and is passionate about health equity for rural and indigenous populations.  He has been an ACLS instructor for close to 30 years and notably his first publication focused on out-of-hospital defibrillation.

Case: A 60-year-old health professional suffers a cardiac arrest while working at a clinic outside the hospital.  An anesthetist is working with him for the procedures.  He confirms pulselessness, initiates CPR, gets a colleague to call 911, and intubates the patient on the floor. He is found to be in ventricular fibrillation and receives two defibrillation attempts with an automatic external defibrillator (AED) at the clinic, and subsequently three more with a primary care ambulance crew enroute to the hospital.  He arrives at the hospital 18 minutes into his arrest and his monitor shows persistent ventricular fibrillation.

Background: Out-of-hospital cardiac arrest (OHCA) is something we have covered extensively on the SGEM over the years. This has included things like therapeutic hypothermia (SGEM#54SGEM#82SGEM#183 and SGEM#275), supraglottic devices (SGEM#247), crowd sourcing CPR (SGEM#143 and SGEM#306), epinephrine (SGEM#238) and IO vs IV (SGEM#231 and SGEM#340).

One issue that has not been covered on the SGEM is pad placement and double sequential external defibrillation.

Clinical Question: Does refractory ventricular fibrillation respond better to standard defibrillation, vector-change defibrillation, or double sequential external defibrillation?

Reference: Cheskes et al. Defibrillation Strategies for Refractory Ventricular Fibrillation. NEJM 2022

  • Population: Ontario patients who were at least 18 years of age and had an OHCA and refractory ventricular fibrillation.
  • Intervention:
    • Vector Change Defibrillation: Pads are placed in an anterior-posterior pad placement after standard anterior-anterior configuration following the third shock with standard defibrillation.
    • Double Sequential External Defibrillation: Pads are placed in both the anterior-anterior and the anterior-posterior pad placements following the third shock with standard defibrillation.
  • Comparison: Standard defibrillation with pads placed in anterior-anterior configuration
  • Outcome:
    • Primary Outcome: Survival to hospital discharge
    • Secondary Outcomes: Termination of ventricular fibrillation, return of spontaneous circulation (ROSC), good Neurologic outcome (modified Rankin scale [mRS] score <3)
  • Trial: Unblinded, cluster-randomized trial with crossover among six paramedic services in rural and urban Canada

Authors’ Conclusions: Among patients with refractory ventricular fibrillation, survival to hospital discharge occurred more frequently among those who received DSED defibrillation or VC defibrillation then among those who received standard defibrillation.”

Quality Checklist for Randomized Clinical Trials:

  1. The study population included or focused on those in the emergency department. No
  2. The patients were adequately randomized. Yes
  3. The randomization process was concealed. Yes
  4. The patients were analyzed in the groups to which they were randomized. Yes
  5. The study patients were recruited consecutively (i.e. no selection bias). Yes
  6. The patients in both groups were similar with respect to prognostic factors. Yes
  7. All participants (patients, clinicians, outcome assessors) were unaware of group allocation. No
  8. All groups were treated equally except for the intervention. Yes
  9. Follow-up was complete (i.e. at least 80% for both groups). Yes
  10. All patient-important outcomes were considered. Yes
  11. The treatment effect was large enough and precise enough to be clinically significant. Yes
  12. Financial conflicts of interest. Disclosure was complete and there were no significant conflicts of interest for any of the authors that would be perceived as potentially influences the submitted work.

Results: They enrolled 405 patients into the study. The mean age was 64 years, over 84% were male, 68% were witnessed arrests, 58% had bystander CPR performed, and median response time was 8 minutes.

Key Result: Greater survival with vector change and double sequence defibrillation compared to standard treatment.

  • Primary Outcome:
    • Vector Change vs standard group 21.7% vs. 13.3%; relative risk 1.71 (95% CI, 1.01 to 2.88).
    • DSED 30.4% vs. standard 13.3%; relative risk 2.21 (95% CI, 1.33 to 3.67)
  • Secondary Outcomes: DSED but not VC defibrillation was associated with a higher percentage of patients having a good neurologic outcome than standard defibrillation (relative risk 2.21 [95% CI, 1.26 to 3.88] and 1.48 [95% CI, 0.81 to 2.71] respectively)


1. Population: These were pre-hospital patients and not ED patients. However, we often have patients code on us in the department or are called to Code Blues somewhere in the hospital. These codes include refractory ventricular fibrillation arrests and likely apply to the hospital setting.

2. Lack of Blinding – This was a double blinded study. The patients were unconscious and unaware of treatment allocation. The outcome assessors were also unaware of group allocation. However, the treating paramedics were aware of the assigned defibrillation strategy. We are unsure if this would have biased the results in a substantial way.

3. Cluster Randomized Control Trials – There is a difference between individual RCTs and cluster randomized trials. Cluster randomization means you cluster groups of individuals as a unit making the number of independent units allocated smaller than the actual number of observations. There are some advantages to performing cluster RCTs that include:

  • Preventing contamination between the intervention and control participants through sharing of information
  • Help with recruitment of participants into the trial
  • Good for public health interventions rather than individual interventions

There are also some disadvantages to cluster RCTs. They can be more difficult to design, analyze appropriately, raise unique ethical challenges, more susceptible to certain biases and from a statistical standpoint less efficient than an individual RCT with the same number of observations.

4. Stopping Early – We have discussed issues around stopping trials early on past SGEM episodes. Depending on why a trial is stopped it can introduce potential bias into the results and lower our confidence of the findings. Some of these problems can be mitigated against by deciding a priori conditions that would cause a trial to be halted. We will put some references in at the end to read about this issue further.

This trial was not stopped for benefit but rather because of COVID. The data and safety monitoring board determined that operational challenges of the pandemic (donning full personal protective equipment, performing aerosol-generating medical procedures, and longer response times due to staffing shortages) necessitated the stopping of the trial. Their power calculation called for 930 patients, and they stopped at 405 (44%).

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We agree with the authors’ conclusions.

SGEM Bottom Line: This represents a potential practice changing article and we should consider incorporate this strategy into our treatment of refractory ventricular fibrillation patients.

Case Resolution: You change the vectors of the pads to anterior-posterior, shock again and are successful in terminating the ventricular fibrillation. He is loaded up into the ambulance and transported to the local hospital ED.

Dr. Sean Moore

Clinical Application: I would start with implementing a protocol for anterior-posterior pad placement on patients with OHCAs or those at risk of OHCAs during transport. If this new protocol is successfully implemented, you could look at having two defibrillators on each ambulance. Listen to the SGEM podcast to hear us expand on this even further.

What Do I Tell the Patient? The patient is unconscious, and we will not be speaking to them during the resuscitation. However, we may mention to the family observing the event that we will try additional strategies to get the patient out of the VF arrest.

Keener Kontest: Last weeks’ winner were Dr. Cindy Bitter and Dr. Steven Steltz. They knew that about 25% of IHCA patients survive.

Listen to the podcast to hear this weeks’ trivia question. If you know the answer, send an email to with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.

Other FOAMed:

  • First10EM: Dose VF-  A double sequential defibrillation game changer?
  • St. Emlyn’s: Alternative Defibrillation Strategies in Refractory VF
  • REBEL EM: Defibrillation Strategies for Refractory Ventricular Fibrillation

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics Guide to Emergency Medicine.


  1. Lievre M, Menard J, Bruckert E et al. Premature discontinuation of clinical trial for reasons not related to efficacy, safety, or feasibility. BMJ 2001; 322: 603-5.
  2. Psaty BM, Rennie D. Stopping medical research to save money. A broken pact with researchers and patients. JAMA 2003; 289: 2128-31.
  3. Chopra SS. Industry funding of clinical trials: benefit or bias? JAMA 2003; 290: 113-4.
  4. Montori VM, Devereaux PJ, Adhikari NK et al. Randomized trials stopped early for benefit: a systematic review. JAMA 2005; 294: 2203-2209.
  5. Bassler D, Matthias et al. Stopping randomized trials early for benefit and estimation of treatment effects: systematic review and meta-regression analysis. JAMA 2010; 303: 1180-1187.
  6. Briel, M, Bassler, D, Wang, AT, et al. The dangers of stopping a trial too early. JBJS 2012; 94: 56-60.
  7. Viele, K, McGlothlin, A, & Broglio, K. Interpretation of clinical trials that stopped early. JAMA 2016; 315: 1646-1647.
  8. Guyatt, GH, Briel, M, Glasziou, P, et al. Problems of stopping trials early. BMJ 2012; 344.