Alternate Defibrillation Strategies for Refractory Ventricular Fibrillation

Mechanism Matters

• • Without fully rehashing the strengths of the DOSE-VF RCT, this secondary analysis does a commendable job at attempting to establish the mechanism behind the survival benefits described for VC and DSED in the original trial. Perhaps more noteworthy, however, is identifying the feasibility of using time in VF as a modifiable resuscitation target. While the recurrence of VF well before rhythm checks is to be expected,⁸ the clear trend in reduction of time in VF with DSED and VC can reasonably explain improved outcomes. Even with active CPR, ongoing VF contributes to cardiac ischemia, which, in turn, results in myocardium that is progressively more difficult to defibrillate.⁹ 
    
  • While this study falls short of demonstrating causality between time in VF and improved survival, the plausibility is more than enough to influence clinical practices. Furthermore, the results are congruent with emerging (though underpowered) data suggesting the benefits of alternate defibrillation strategies by both increasing total joules and more directly engaging the left ventricle, though meta-analyses to date show the need for more studies similar to the DOSE-VF RCT in order to clearly demonstrate benefit. ^10-13
  • It is additionally important to recognize that all of the shocks delivered in the DSED arm of this trial were intentionally performed sequentially with a short delay between shocks, as opposed to simultaneously. With the understanding that defibrillation is probabilistic – that is, defibrillation success increases with the amount of joules delivered – there is reason to believe that simultaneous shocks could be more effective at resolving arrhythmias. ^7,9 While the authors understandably included this delay in order to reduce the theoretical risk of device damage, it nonetheless represents a missed opportunity to evaluate this modality.^16,17 This is notable, as animal models suggest that some sequential time delays (50ms in particular) can actually result in worse outcomes by retriggering VF if the initial shock was successful.¹⁸

Battle of the Vectors

• • With respect to the rhythm analysis, the data does appear to support the author’s assertion that the difference in time in VF is secondary to the type of shock received. Although the decision to run this as a per-protocol study offers reduced protection against randomization, the baseline rhythms of each protocol were nearly identical, and remarkably few defibrillation files were lost given the size of the study. Likewise, there is a clear reduction in time spent in VF after intervention which is consistent from shock to shock, and although there are legitimate concerns regarding the external validity of DOSE-VF due to excellent EMS care, this is likely only to affect the magnitude of the impact, rather than the presence of it at all.
  • From a clinical standpoint, it is difficult not to notice the clear difference in times between the VC and DSED treatment arms, and a 15 second difference between the two feels like it could be relevant to patient outcomes. This study is unfortunately too underpowered to demonstrate statistical significance between the two, but personally, a trend here is more than enough to be practice changing and lead to DSED being used over VC.
  • In a resource-rich setting where obtaining a second defibrillator is easy, the potential upside is clear and the downsides are few, with just the (low) theoretical risk of damage to the defibrillator to consider16,17. For this reason and to minimize delays later in care, posterior pads should likely be applied during initial transfer onto the ED stretcher for any patient that was noted to be in VF prior to arrival.
    • Although there are case reports of defibrillator damage from simultaneous shocks, this risk appears to be relatively rare at a reported 0.4%, and it can be further reduced by ensuring a perpendicular angling of the shock vectors.¹⁶ Those who remained concerned, however, may be reassured that zero devices were damaged during the DOSE-VF trial, which used sequential defibrillation. Likewise, a retrospective review of over 1000 EMS cases revealed that 100% of device damage occurred during simultaneous, not sequential defibrillation attempts, indicating the risk is likely appreciably lower with intentional delay.¹⁷
  • Further studies, however, are certainly needed to justify two defibrillators being available in settings where this would be cost prohibitive, and device damage even more so. In these scenarios, VC defibrillation appears to be ideal, as both the survival benefit and the reduction in time spent in VF are still quite appreciable for the VC group . Although taking the time to re-orient the pads would decidedly prolong a pulse check and reduce chest compression fracture, it seems likely that this effort represents a net benefit for patients in refractory VF by more directly orienting shocks towards the ischemic left ventricle.

Future Directions

• • While the authors themselves touch on some aspects of this, there are multiple conclusions that can be drawn from reducing time in VF from 113 seconds to 83 seconds with DSED after shock #4. The most obvious of these is the suggestion that DSED should be employed as early as possible in VF, well before it could be considered refractory. Further studies are needed to mathematically back that decision (and are currently in progress), but earlier initiation of DSED is more than reasonable based on current data given the potential upside. 
  • If you fully buy into the idea that time in VF directly leads to worse outcomes, however, there is the more interesting implication that standard ACLS should be modified in refractory VF. With medical options being largely ineffective and 83 out of 120 seconds being VF, should we be less aggressively prioritizing chest compression fraction in favor of more frequent rhythm checks and shocks? Personally, the data here is not convincing enough to change clinical practices in this regard, but should remain a topic of conversation.