Double Sequential Defibrillation in Refractory V-Fib: Does It Deliver?

Double Sequential External Defibrillation (DSED) involves delivering two rapid, sequential shocks from two separate defibrillators, using two sets of pads placed in different positions—typically anterolateral and anterior-posterior.

Proposed Mechanisms:

• Higher cumulative energy delivered to the myocardium.
• Altering the defibrillation vector to capture more myocardial tissue.
• Reducing transthoracic impedance, potentially improving shock efficacy.

The idea is that if standard defibrillation isn’t working, hitting the heart with different vectors and sequential energy might disrupt the arrhythmia more effectively.

Prior to the DOSE-VF trial, several observational studies explored the efficacy of DSED in treating refractory VF during out-of-hospital cardiac arrests (OHCA).

1. The Emerson et al. (2017): A retrospective observational study by the London Ambulance Service found that about one-third of patients treated with DSED achieved pre-hospital ROSC, and 7% survived to hospital discharge, with outcomes similar to those receiving standard defibrillation. The study concluded there was no clear benefit of DSD over standard defibrillation but emphasized the need for randomized trials to explore its potential value.
2. Mapp et al. (2019): This matched case-control study found that prehospital DSED did not improve survival to hospital admission compared to conventional defibrillation, with survival rates of 48.0% for DSD and 50.5% for standard therapy (OR 0.91, 95% CI: 0.40-2.1), indicating no significant difference between groups.
3. Cheskes et al. (2019): A retrospective review found that early application of DSED (defibrillation attempts 4-8) was associated with higher VF termination (29.4% vs. 17.5%) and ROSC rates (15.7% vs. 5.4%) compared to standard defibrillation, suggesting earlier DSD may improve refractory VF outcomes.
4. Delorenzo et al (2019): This systematic review and meta-analysis of 499 patients (19% received DSED) found no significant effect of DSD on survival to hospital discharge (OR 0.69, 95% CI 0.30-1.60), event survival (OR 0.98, 95% CI 0.59-1.62), or ROSC (OR 0.86, 95% CI 0.49-1.48), concluding that its effectiveness remains unclear and requires further prospective studies.

The observational nature of these studies introduced several limitations:

• Selection Bias: Patients selected for DSED may have differed systematically from those receiving standard defibrillation, potentially influencing outcomes.
• Confounding Variables: Unmeasured factors, such as variations in EMS protocols, responder experience, and patient characteristics, could have affected results.
• Small Sample Sizes: Limited numbers of patients reduced the statistical power to detect significant differences.

Source

Cheskes S, Verbeek PR, Drennan IR, McLeod SL, Turner L, Pinto R, Feldman M, Davis M, Vaillancourt C, Morrison LJ, Dorian P, Scales DC. Defibrillation Strategies for Refractory Ventricular Fibrillation. N Engl J Med. 2022 Nov 24;387(21):1947-1956. doi: 10.1056/NEJMoa2207304. Epub 2022 Nov 6. PMID: 36342151.

Study Design

• Design: Cluster-randomized controlled trial across six EMS systems in Ontario, Canada.
• Patients: Adults with refractory VF after at least three standard defibrillation attempts.
• Interventions:
• Standard Defibrillation
• Vector Change (VC) Defibrillation (changing pad position to anterior-posterior)
• Double Sequential External Defibrillation (DSED)

Key Results:

Author Conclusion

“Among patients with refractory ventricular fibrillation, survival to hospital discharge occurred more frequently among those who received DSED or VC defibrillation than among those who received standard defibrillation.”

Critical Appraisal & Analysis

For in-depth critical appraisal, including strengths, limitations, and caveats, review these FOAMed analyses:

1. REBELEM: Defibrillation Strategies for Refractory Ventricular Fibrillation
2. First10EM: Dose VF: A double sequential defibrillation game changer?
3. St. Emlyn’s: Alternative defibrillation strategies in refractory VF. The Dose VF trial. 
4. Skeptics Guide to EM: Shock Me- Double sequential or vector change for OHCAs with refractory ventricular fibrillation
5. TheBottomLine: Defibrillation Strategies for Refractory Ventricular Fibrillation

Strengths

• Robust Study Design: As a randomized controlled trial with a cluster crossover design, it minimized biases related to paramedic performance variability and enhanced the reliability of its findings.
• Standardized Protocols: The implementation of uniform resuscitation protocols and specific guidelines for both DSED and VC defibrillation ensured consistency in treatment across different EMS services.
• Outcome Assessor Blinding: Blinding of those assessing outcomes reduced potential bias in evaluating the effectiveness of the defibrillation strategies.
• Comprehensive Data Collection: The trial's thorough data collection, including metrics like CPR quality and adherence to protocols, provided a detailed understanding of the interventions' impacts.

Limitations

• Early Termination & Sample Size: The trial was stopped early due to COVID-19, leading to a smaller-than-planned sample size and a potential overestimation of effect size, particularly for DSED.
• Short-Term Outcome Focus: The study measured neurological outcomes only at hospital discharge, leaving uncertainty about long-term functional recovery beyond that point.
• Equipment & Resource Constraints: DSED requires two defibrillators and additional coordination, which may not be feasible in all EMS or hospital settings, especially in resource-limited environments.
• Logistical & Training Challenges: The practical implementation of DSED requires precise team coordination, which may not be easily standardized across different prehospital systems.

The theoretical risk of defibrillator damage from DSED arises from concerns about potential electrical feedback when delivering two nearly simultaneous shocks from separate defibrillators.

Potential for Electrical Feedback

• Mechanism: In DSED, two defibrillators are connected to the patient with separate pad placements, and shocks are delivered either nearly simultaneously or within milliseconds of each other. There’s a theoretical risk that electrical current from one defibrillator could travel backward through the circuitry of the second defibrillator, potentially causing damage.
• Why It’s a Concern: Defibrillators are designed to deliver high-voltage energy outward, not to handle incoming currents. A strong electrical feedback could theoretically overload internal components like capacitors, resistors, or circuit boards.
• Modern Safeguards: Contemporary defibrillators are equipped with protection circuits designed to prevent electrical backflow. These features significantly reduce the likelihood of damage, even under unusual conditions like DSED. The theoretical risk primarily stems from concerns related to older defibrillator models that lacked these modern protective mechanisms.

The Available Evidence

• The DOSE-VF Trial (2022): In this large, randomized controlled trial, no cases of defibrillator damage or malfunction were reported during DSED. This suggests that modern defibrillators are capable of handling the demands of DSED without sustaining damage.
• Gerstein et al. (2018): While defibrillator damage from DSED has been largely theoretical, this case report documented equipment damage during synchronized dual-dose cardioversion. This indicates that while the risk is extremely rare, it can occur, particularly when shocks are delivered in true synchronization. However, DSED typically involves sequential shocks without synchronization, which theoretically reduces this risk.

While the theoretical risk of defibrillator damage from DSED exists due to concerns about electrical feedback, real-world evidence suggests this risk is extremely rare. Large studies like the DOSE-VF trial reported no cases of defibrillator damage, and isolated reports of equipment failure are limited to a case involving synchronized shocks, which differs from the sequential technique used in DSED.

While Double Sequential External Defibrillation (DSED) shows promise in improving survival and neurologically intact outcomes for patients with refractory ventricular fibrillation, as seen in the DOSE-VF trial, the evidence remains limited. The trial’s early termination and the scarcity of large, randomized studies mean that the true effectiveness of DSED is still uncertain. However, DSED appears to be safe when performed correctly, with no reported cases of defibrillator damage in major studies and only rare equipment issues related to synchronized shocks, not the sequential technique used in DSED. For now, DSED is a reasonable option when standard defibrillation fails.

Dr. Hedayati on Critical Care Now does a great overview on the history and literature on DSED in this video:

1. Cheskes S, Wudwud A, Turner L, McLeod S, Summers J, Morrison LJ, Verbeek PR. The impact of double sequential external defibrillation on termination of refractory ventricular fibrillation during out-of-hospital cardiac arrest. Resuscitation. 2019 Jun;139:275-281. doi: 10.1016/j.resuscitation.2019.04.038. Epub 2019 May 3. PMID: 31059670.
2. Cheskes S, Verbeek PR, Drennan IR, McLeod SL, Turner L, Pinto R, Feldman M, Davis M, Vaillancourt C, Morrison LJ, Dorian P, Scales DC. Defibrillation Strategies for Refractory Ventricular Fibrillation. N Engl J Med. 2022 Nov 24;387(21):1947-1956. doi: 10.1056/NEJMoa2207304. Epub 2022 Nov 6. PMID: 36342151.
3. Delorenzo A, Nehme Z, Yates J, Bernard S, Smith K. Double sequential external defibrillation for refractory ventricular fibrillation out-of-hospital cardiac arrest: A systematic review and meta-analysis. Resuscitation. 2019 Feb;135:124-129. doi: 10.1016/j.resuscitation.2018.10.025. Epub 2018 Oct 26. PMID: 30612966.
4. Emmerson AC, Whitbread M, Fothergill RT. Double sequential defibrillation therapy for out-of-hospital cardiac arrests: The London experience. Resuscitation. 2017 Aug;117:97-101. doi: 10.1016/j.resuscitation.2017.06.011. Epub 2017 Jun 15. PMID: 28624593.
5. Gerstein NS, McLean AR, Stecker EC, Schulman PM. External Defibrillator Damage Associated With Attempted Synchronized Dual-Dose Cardioversion. Ann Emerg Med. 2018 Jan;71(1):109-112. doi: 10.1016/j.annemergmed.2017.04.005. Epub 2017 May 27. PMID: 28559035.
6. Mapp JG, Hans AJ, Darrington AM, Ross EM, Ho CC, Miramontes DA, Harper SA, Wampler DA; Prehospital Research and Innovation in Military and Expeditionary Environments (PRIME) Research Group. Prehospital Double Sequential Defibrillation: A Matched Case-Control Study. Acad Emerg Med. 2019 Sep;26(9):994-1001. doi: 10.1111/acem.13672. Epub 2019 Jan 6. PMID: 30537337.