Early defibrillation is a key step in the management of cardiac arrest patients patients with VF/VT In many cases defibrillation does indeed revert the patient to a better rhythm, but not always. I find that there are two groups of patients that we struggle with. The first is the group whom I do not seem to be able to get out of a shockable rhythm. I defibrillate them, but it seems that they do not change rhythm, they just stay in VF/VT. The second group are the ones who I can get out of VF/VT into what looks like a perfusing rhythm, but who then keep reverting back to VF/VT after a period of time. Somewhat simplistically, I think of the solutions to these problems differently. Group 1 need more, or more effective joules. Group 2 need drugs. If we focus on the more/more effective joules then what strategies are available to us?
Defibrillation traditionally takes place with the chest pads in the antero-lateral (AL) position, but there are alternatives. Antero-posterior (AP) pad positions are commonly used as an alternative and in smaller children where it might be tricky to get the pads to be separated if an AL position is attempted. We recently reviewed a trial comparing AP and AL positions for cardioversion of AF which showed a benefit to the AL position, but there was a significant concern there as to whether we can translate that evidence to VF/VT management. That said, if I have a patient who appears to be difficult to defibrillate with pads in the AL position I have flipped them into an AP position in the hope that it will work, an anecdotally it has had limited success.
There is also the option of Dual-Sequence Defibrillation (DSD), where two defbrillators are used to increase the amount and direction of energy transmitted through the chest on the same patient, at the same time. It looks pretty wild to do in practice and I’ve only done this a handful of times. The evidence based for it has been weak and there have been concerns about whether it may damage defibrillators.
The bottom line is that until now we do not really know whether AL is better than AP, nor whether DSD is better than either. This week we have a trial in the NEJM that might help us answer that question. The abstract is below, but as always we strongly recommend you read the full paper yourself.
What kind of trial is this?
It’s a randomised controlled trial which is what we want to see when testing/comparing interventions. Ideally, we would want to see the interventions blinded to both participants and patients, but in this case that’s clearly impossible and so this is an open-label randomised controlled trial. Patients were randomised in clusters. What this means is that the four paramedic services involved all used one technique for a period of time, before then changing to one of the others for a period of time, nad then swapping again. So all services used the AL, AP and the DSD approach for a period of time during the study.
Tell me about the patients.
Patients were adults deemed to be in cardiac arrest with refractory VF rhythm as determined by the treating paramedics. Patients suffering a traumatic cardiac arrest, patients with pre-existing DNARs, and those suffering cardiac arrest secondary to drowning, hypothermia, hanging or suspected drug overdose were excluded.
Refractory VF was defined as someone who still requires defibrillation after three prior shocks. All prior shocks were given in the AL position. Depending on which cluster the paramedics were in they would then either stay AL, or change to AP or DSD.
Tell me about the interventions.
The positions of the pads are shown on the infographic. For DSD it’s important to note that these are sequential and not simultaneous shocks. In the past it has been suggested that in DSD the two defibs are fired at the same time. Performing the shocks sequentially is thought to have less chance of damaging the (other) defibrillator. In this study the shocks were given about a second apart. The authors refer to an AP position as a vector change (VC) in the paper.
Post ROSC care was not standardised and some have argued that this may influence the results, although as the patients were in the same health economies this is likely to be a relatively small effect.
What are the outcomes?
The main outcome was survival to hospital discharge. Secondary analyses included success of defibrillation and neurological outcomes (on the Rankin scale with a score of 2 or better. A score of 2 is defined as ‘slight disability’. In general we (St Emlyn’s) prefer neurological outcomes to be the main outcome measure, but survival is a reasonable alternative.
What are the main results.
405 patients were enrolled which was less than the intended 900 +. In terms of allocations, 136 (33.6%) were assigned to the standard group, 144 (35.6%) to the VC group, and 125 (30.9%) to the DSED group.
In terms of the main outcome (survival to hospital discharge) DSD performed best, and AP performed better than AL.
- Survival with DSD 30.4% (38/125 patients)
- Survival with AP 21.7% (31 of 143 patients)
- Survival with AL 13.3% (18 of 135 patients)
Both DSD and AP performed better than AL. DSD clearly has a larger effect but the confidence intervals when comparing it against AP overlap, so we we are a little less certain about the difference between these two techniques. The authors looked at the fragility index of these findings and found it to be 1 for the AP group and 9 for the DSD group.
Should we change practice?
This is the best evidence we have seen for alternative defibrillation strategies in refractory VF and the results are promising. It does seem that persisting with an AL position is the least beneficial and that changing positions, or using DSD may be beneficial.
There are a few issues with the trial. As @first10EM points out, this is not a blinded trial and so it is potentially possible that people tried harder, or for longer with the ‘new’ techniques, but that’s not something that we are likely to resolve any time soon. The trial was also stopped early which risks a type 1 error, or at least an overestimate of the treatment effect. That said, there is clear logic in doing something different if the initial strategy (AL pads) does not work. It makes sense that if AL has not worked for three shocks then it’s less likely to work for the 4th or subsequent shocks. This is important for those who might consider using AP or DSD as their initial choice. This paper clearly cannot tell us which to use first (although I’d quite like someone to do that trial), as it may well be that AL is in fact the best option initially, and that AP or DSD are ‘rescue techniques’ for when that fails.
There are some other challenges to institute DSD in practice. If you decide to do this then you will need to check whether it affects warranties and whether you can physically fit four pads onto the chest. Our current pads in Virchester are huge and I just don’t think it’s possible. Prehospitally, the defib pads are smaller and so definitely possible, but we usually use a LUCAS there and so dismantling that and placing a posterior pad will need some planning. You will also need to train and simulate these cases if you are planning on delivering these strategies.
For me I think this trial will encourage me to use a change in pad position/DSD as an early option for refractory VF. DSD seems to be the better option and this paper would justify that option in practice Having a published study will certainly help in the future as in the past I’ve been given a few rather odd looks when suggesting it!
The patients I think most likely to benefit are those in the group 1 that we discussed at the beginning of the article (those that do not come out of VF at all), but of course that is just my opinion rather than based on the evidence in the trial.
References & further reading
Defibrillation Strategies for Refractory Ventricular Fibrillation https://www.nejm.org/doi/pdf/10.1056/NEJMoa2207304
Double sequential external defibrillation for refractory ventricular fibrillation: The DOSE VF pilot randomized controlled trial. https://pubmed.ncbi.nlm.nih.gov/32084567/
Simon Carley, “JC: AP or AL position for cardioversion? St Emlyn’s,” in St.Emlyn’s, May 1, 2022, https://www.stemlynsblog.org/jc-ap-or-al-position-for-cardioversion-st-emlyns/.
Simon Carley, “Dual Axis Defibrillation & #ResusFriday at St.Emlyn’s,” in St.Emlyn’s, May 21, 2017, https://www.stemlynsblog.org/dual-axis-defibrillation-resusfriday-at-st-emlyns/.
Boehm K, Keyes D, Mader L, Moccia J. First Report of Survival in Refractory Ventricular Fibrillation After Dual-Axis Defibrillation and Esmolol Administration. West J Emerg Med. 2016;17(6):762-765. [PubMed]
Leacock B. Double simultaneous defibrillators for refractory ventricular fibrillation. J Emerg Med. 2014;46(4):472-474. [PubMed]
Hoch D, Batsford W, Greenberg S, et al. Double sequential external shocks for refractory ventricular fibrillation. J Am Coll Cardiol. 1994;23(5):1141-1145. [PubMed]
Cabañas J, Myers J, Williams J, De M, Bachman M. Double Sequential External Defibrillation in Out-of-Hospital Refractory Ventricular Fibrillation: A Report of Ten Cases. Prehosp Emerg Care. 2015;19(1):126-130. [PubMed]
Hoch DH, Batsford WP, Greenberg SM, et al. Double sequential external shocks for refractory ventricular fibrillation. Journal of the American College of Cardiology. 1994;23(5):1141-1145. doi: 10.1016/0735-1097(94)90602-5 [Source]
Lybeck AM, Moy HP, Tan DK. Double Sequential Defibrillation for Refractory Ventricular Fibrillation: A Case Report. Prehospital Emergency Care. 2015;19(4):554-557. doi: 10.3109/10903127.2015.1025155