Refractory ventricular fibrillation (VF) remains one of the most formidable challenges in cardiopulmonary resuscitation. Despite significant advances in the management of out-of-hospital cardiac arrests, some patients do not respond to standard defibrillation techniques, seriously compromising their chances of survival. In this context, new defibrillation approaches have emerged in recent years, particularly double sequential external defibrillation (DSED) and vector change (VC) defibrillation. This article reviews the current data on these innovative techniques, based on the results of the most recent and relevant studies.
Double Sequential External Defibrillation: Principles and Mechanisms of Action
DSED involves using two defibrillators simultaneously, with electrodes placed in two different positions (usually anterolateral and anteroposterior), to deliver two shocks in rapid succession. This approach aims to overcome the resistance of some VFs to standard defibrillation techniques.
Several mechanisms of action have been proposed to explain the potential effectiveness of DSED:
- Increase in total energy delivered
- Creation of multiple current vectors across the myocardium
- Reduction of transthoracic impedance
- “Conditioning” effect of the first shock, making the heart more sensitive to the second
The DOSE VF study, published by Cheskes et al. in 2022, represents to date the largest and most rigorous randomized clinical trial on the use of DSED and VC in the treatment of refractory VF. This study included 405 patients divided into three groups: standard defibrillation, DSED, and VC.
Main results:
– Survival to hospital discharge:
DSED: 30.4%
VC: 21.7%
Standard: 13.3%
– VF termination:
DSED: 84.0%
VC: 79.9%
Standard: 67.6%
– Return of spontaneous circulation (ROSC):
DSED: 46.4%
VC: 35.4%
Standard: 26.5%
These results suggest a superiority of DSED and, to a lesser extent, VC compared to standard defibrillation for the treatment of refractory VF. However, it is important to note that the study was prematurely stopped due to the COVID-19 pandemic, which could have influenced the results.
Secondary Analysis of DOSE VF: Shock-Refractory vs Recurrent VF
A secondary analysis of the DOSE VF study sought to determine whether the effectiveness of DSED and VC differed between patients with shock-refractory VF (persistent despite defibrillation attempts) and those with recurrent VF (reappearing after initially successful defibrillation).
Main findings:
- DSED proved superior to standard defibrillation for survival to hospital discharge in both the shock-refractory VF group and the recurrent VF group.
- VC showed no significant difference compared to standard defibrillation in both groups.
- DSED was particularly effective in the shock-refractory VF group, where no patient survived with standard defibrillation.
These results suggest that DSED could be particularly beneficial for patients with truly shock-refractory VF, who generally have a very poor prognosis with standard techniques.
Meta-analyses: A More Nuanced View
Two recent meta-analyses have sought to synthesize available data on the effectiveness of DSED compared to standard defibrillation.
The meta-analysis by Delorenzo et al. included 7 studies (1 randomized trial and 6 observational studies) totaling 1,632 patients. Unlike the DOSE VF study, this meta-analysis found no significant difference between DSED and standard defibrillation for survival to hospital discharge, ROSC, or good neurological outcome.
The meta-analysis by Li et al., including 10 studies with 1,347 patients, reached similar conclusions, showing no significant superiority of DSED for main outcome measures.
How to explain these divergences?
Several factors can explain the differences between the results of the DOSE VF study and those of the meta-analyses:
- Quality of included studies: The meta-analyses incorporated many observational studies, potentially subject to biases.
- Heterogeneity of protocols: Definitions of refractory VF and DSED techniques varied between studies.
- Timing of DSED: The DOSE VF study applied DSED earlier than in many observational studies.
- Sample sizes: The DOSE VF study, although prematurely stopped, remains the largest individual study on the subject.
Safety of DSED: The Risk of Defibrillator Damage
A frequent concern regarding DSED is the potential risk of damage to defibrillators. A study conducted by Drennan et al. specifically examined this issue through a survey of emergency medical services, authors of previous publications, and defibrillator manufacturers.
Main results:
– Overall incidence of damage: 0.4% of cases (5 out of 1,130)
– Estimated incidence per shock: between 0.11% and 0.22%
– All cases of damage occurred with the simultaneous technique
– No damage reported with the sequential technique
These results are reassuring and suggest that the risk of equipment damage should not be a major obstacle to the use of DSED, particularly if the sequential technique is favored.
Implications for Clinical Practice
Although current data are promising, particularly those from the DOSE VF study, it is important to note that DSED is not yet routinely recommended by Heart and Stroke. However, these results open new perspectives for the management of refractory VF.
Points to consider for potential implementation of DSED:
- Adequate staff training: DSED requires precise coordination and a good understanding of the technique.
- Equipment availability: DSED requires two defibrillators, which can pose logistical challenges in some contexts.
- Standardized protocols: It is crucial to clearly define when and how to apply DSED to maximize its effectiveness and safety.
- Monitoring and evaluation: Implementation of DSED should be accompanied by rigorous data collection to assess its long-term impact.
Future Perspectives
Several questions remain unanswered and deserve to be explored in future research:
- Optimal timing of DSED: At what point in the resuscitation process should DSED be introduced to maximize its benefits?
- Patient selection: Are there subgroups of patients who would particularly benefit from DSED?
- Technical optimization: What is the best electrode configuration and what interval between shocks should be targeted?
- Long-term results: What is the impact of DSED on long-term patient survival and quality of life?
- Cost-effectiveness analysis: Is DSED an economically viable option compared to standard techniques?
Double sequential external defibrillation represents an innovative and promising approach for the treatment of refractory ventricular fibrillation. The results of the DOSE VF study are particularly encouraging, suggesting a significant improvement in survival with this technique. However, recent meta-analyses provide a more nuanced view, highlighting the need for further research.
DSED could potentially revolutionize the management of some of the most difficult-to-treat cardiac arrests. Nevertheless, its implementation in routine clinical practice will require careful evaluation of its effectiveness, safety, and feasibility in various care settings.
As healthcare professionals, it is crucial to stay informed of these advances while maintaining a critical eye on the available evidence. The future will tell if DSED will one day become a standard of care for refractory VF, but it already represents a fascinating research avenue in our constant quest to improve chances of survival after cardiac arrest.
