Shock Differently - Out of Hospital Cardiac Arrest

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Background 

Out of hospital cardiac arrest (OOHCA) represents a great cause of morbidity and mortality. Approximately 350,000 cardiac arrests occur in North America annually and 20% can be attributed to Ventricular tachydysrhythmias (i.e. ventricular tachycardia [v fib] and ventricular tachycardia [v tach]without a pulse).(1,2,3) While overall survival to hospital discharge remains poor in OOHCA, approximately 10%,(2,3) patients in v fib/v tach have greater survival.(4) This higher likelihood of attaining return of spontaneous circulation (ROSC) is contingent upon high quality CPR and early defibrillation. (2,3,4)  However, as many as 20% patients with v fib/v tach may have refractory dysrhythmias(4) in which antiarrhythmics and defibrillation are unsuccessful. In this case, one must consider alternative strategies to abort the arrhythmia which may fall outside the ACLS standard protocols. (2) There are 2 possible alternative defibrillation strategies that have been suggested in the past. One therapy is vector change defibrillation, in which the defibrillation pads are placed in the anterior posterior configuration to change the direction of the shock delivered through the myocardium. The second is dual sequence defibrillation in which two defibrillators are used, one attached to anterior-posterior pads, and one to anterior-lateral pads which are then deployed within a second of each other, delivering two shocks rapidly to the patient. As of yet, no therapy has been found to be superior.

In 2018, Cheskes et al in Canada decided to examine these therapies and compare their outcomes. They utilized paramedic services to compare outcomes of dual sequence vs vector change defibrillation in regards to survival to hospital discharge as well as termination of v fib, rates of ROSC, and neurologic outcome at discharge. 

Methods

  • This was a cluster-randomized trial with crossover

  • 6 paramedic Canadian services were used with paramedic units being randomly assigned a therapy and then crossing to the other therapy after a set amount of time. 

  • Comparison was standard defibrillation vs vector change and dual sequence defibrillation 

  • Therapies were used in adult OOHCA patients with refractory v fib (patient with v fib who had >3 shocks) 

  • Outcomes evaluated

    • Primary outcome: survival to hospital discharge

    • Secondary outcomes 

      • Termination of v fib

      • ROSC

      • Intact neurologic outcome (modified Rankin score >2)

Results

  • Total: 405 enrolled were patients 

    • Demographics 

      •  Average age was 63.6 yrs

      • 84.4% male

      • 67.9% had witnessed arrests

      • 58% received bystander CPR 

  • Randomization 

    • 136 (33.6%) patients received standard defibrillation 

    • 144 (35.6%) patients received  vector change defibrillation

    • 125 (30.9%)  patients received dual sequence defibrillation 

  • Outcomes

    • Survival 

      • Compared to standard defibrillation

        • Survival to hospital discharge was more common in dual sequence vs defibrillation (38 (30.4%) vs. 18 (13.3%); relative risk, 2.21; 95% confidence interval [CI], 1.33 to 3.67)

        • Survival to hospital discharge was more common in vector change group  (31(21.7)% vs. 18 (13.3%); relative risk, 1.71; 95% CI, 1.01 to 2.88)

      • The overall test for differences in survival between the groups was statistically significant (P=0.0009) 

      • However, a fragility index suggested that if 9 patients in the dual sequence group or 1 patient in the vector change group had not survived, this outcome would have been statistically insignificant. 

    • Termination of v fib 

      • Compared to standard defibrillation, vector change had greater v fib termination (67.6% vs 79.9%)

      • Compared to standard defibrillation, dual sequence had greater v fib termination (67.6% vs 84%)

    • ROSC rates 

      • Compared to standard defibrillation, vector change had greater ROSC (26.5% vs 35.4%)

      • Compared to standard defibrillation, dual sequencer had feater ROSC (26.5% vs 46.4%)

    • Neurologic outcome (modified Rankin scale less than or equal to 2)

      • Dual sequence had greater neurologic outcomes compared to vector change (relative risk, 2.21 [95% CI, 1.26 to 3.88] and 1.48 [95% CI, 0.81 to 2.71])

      • Both were superior to standard defibrillation (11.2%)

Limitations and Discussion

In this study, alternative defibrillation strategies were employed in the prehospital setting for refractory v fib. Based on the data collected, there does appear to be utility in using vector change or dual sequence defibrillation, with dual sequence appearing to have greater outcomes. Some strengths of the study include the novel study method randomization and crossover of the interventions with the paramedic units. For a prehospital study, the randomization was good with most patients receiving their assigned therapy. Additionally, many have noted concern that dual sequence defibrillation may damage the defibrillator device, but no such events were seen in this study. 

However, there are some notable limitations to the study. Firstly, the study overall seems to lack patient enrollment, which raises concern that the study is underpowered. The authors themselves calculated a fragility index that indicates crossover of as few as 1 patient may have rendered the outcome data insignificant. Lastly, the study was interrupted and ended prematurely due to the  COVID-19 pandemic in 2020, which affected the issues above.

Conclusion  

This cluster randomized study showed that OOHCA patients with refractory v fib had increased survival to hospital discharge with both dual sequence and vector change defibrillation compared to standard defibrillation. However, the study is underpowered, experienced several real world disruptions/difficulties (i.e. early termination, interruptions from the COVID-19 pandemic, imperfect crossover of interventions), and the data shows fragility when comparing vector change to dual sequence defibrillation. However, it does demonstrate that in refractory v fib, implementing either of these strategies improves achievement of ROSC and survival, and thus provides reasonable adjunctive therapies to utilize in this subset of critically ill patients. 

References

  1. Cheskes S, Verbeek PR, Drennan IR, et al. Defibrillation Strategies for Refractory Ventricular Fibrillation. N Engl J Med. 2022;387(21):1947-1956. doi:10.1056/NEJMoa2207304 

  2. Ong MEH, Perkins GD, Cariou A. Out-of-hospital cardiac arrest: prehospital management. Lancet. 2018;391(10124):980-988. doi:10.1016/S0140-6736(18)30316-7

  3. Pourmand A, Galvis J, Yamane D. The controversial role of dual sequential defibrillation in shockable cardiac arrest. Am J Emerg Med. 2018;36(9):1674-1679. doi:10.1016/j.ajem.2018.05.078

  4. Deakin CD, Morley P, Soar J, Drennan IR. Double (dual) sequential defibrillation for refractory ventricular fibrillation cardiac arrest: A systematic review. Resuscitation. 2020;155:24-31. doi:10.1016/j.resuscitation.2020.06.008

  5. Deakin CD. Dual sequential defibrillation: Hold your horses!. Resuscitation. 2020;150:189-190. doi:10.1016/j.resuscitation.2020.03.001

Authorship

Written by Kelly Tillotson, MD, EMS Fellow, University of Cincinnati Department of Emergency Medicine

Peer Review, Editing, and Posting by Jeffery Hill, MD MEd, Associate Professor, University of Cincinnati Department of Emergency Medicine

Cite As: Tillotson, K., Hill, J. Shock Differently - Out of Hospital Cardiac Arrest. www.tamingthesru.com. www.tamingthesru.com/blog/journalclub/oohca-dual-sequence. 6/28/24