JC: AP or AL position for cardioversion? St Emlyn’s

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Defibrillation is a core skill in emergency medicine. Traditionally we are taught that an anterior-lateral (AL) placement of pads is preferable, although an anterior-posterior (AP) position can be used if AL does not work. This probably arose because placing pads in the AL position is physically easier as if the goal is to transmit electricity across the heart then an AP position would (at first glance) seem to be more logical. It was also the case when I was training that defibrillation was much ‘dramatic’ than it is now. When I started training we were still using hand paddles and jelly applied to the paddles. The introduction of defib contact pads and now full hands-free pads is clearly an improvement in terms of safety and clinical outcome……., but the hand paddles and jelly was just more dramatic (although as the clip below shows, there are many things I don’t miss about the old ways). I’ve also noticed that Carter cannot pronounce Laryngoscope.

That said, there are many proponents of an AP position, especially in less urgent conditions such as the cardioversion of atrial fibrillation. This is an EM procedure, although we do it less these days following the publication of a randomised controlled trial that suggested that observing with pharmacological interventions up to 48 hours was acceptable. You can read more about that trial here.

If we do decide to proceed with a cardioversion though, should we go for an AP or AL approach? Fortunately there is a recently published trial that can help us answer this question. The abstract is below, and as always we recommend you read the full paper and come to your own conclusions.

What type of paper is this?

This is a randomised controlled trial, which is what we would like to see as this is a trial of a clinical intervention and an RCT gives us a reasonable chance of eliminating many biases that may impact the results.

What did they do?

This study looked at whether AP or AL paddle/pad positions made a difference. Patients were randomised in blocks and stratified by site. This is an important part of randomisation in many clinical trials, especially those using multiple sites. Block randomisation ensures that each site gets a fair chance of reasonably equal numbers of patients in each group. Stratification ensures that the trial gets roughly equal numbers of patients in each treatment group as related to severity/likelihood of success.

Who did they study?

In this study the focus was on patients undergoing elective cardioversion of AF. From an EM perspective this is not quite the group of patients that we see in the ED, and it’s clearly not the same as those we defibrillate for immediately life threatening conditions such as VF/VT. It’s also arguably not the same as EM cardioversion for AF as the patient characteristics and method of sedation/co-drug use may be different. This issue is a common problem in critical appraisal and it’s an important question for us to address as to whether these results are transferable to practice. Obviously there will be a degree of judgement here, but my view is that in the absence of other trials in the EM population then it’s probably the best evidence we will be able to get. 468 patients were randomised in this study.

Tell me about the outcomes.

Defining outcomes is an essential component of any clinical trial and in this paper it’s a pretty hard end point. The principal outcome was whether the patient cardioverted to sinus rhythm after the first shock and stayed in that rhythm at 1 min post shock. Secondary outcomes were whether they were in sinus 1min after the last shock (up to a max of 4 shocks). I think you can argue which of these is the more important outcome, but as both are reported it does not matter too much.

What were the interventions?

Patients were defibrillated in either the AP or AL paddle positions. All shocks were synchronised shocks and at escalating energy levels starting at 100J up to 360J as per current guidelines.

Was AP or AL best?

For the primary outcome in this study more patients 126/234 (54%) of patients in the AL group cardioverted as compared to 77/234 (33%) in the AP position. This is quite a large difference, an ARR of 22% and an Number needed to treat (NNT) of 4.5 which is remarkable.

For the secondary outcome of whether they were in sinus rhythm after up to 4 shocks then 93% were in sinus with AL as compared to 85% with AP. That’s an ARR of 8% and an NNT of 12.5 on my calcs (but 14 in the paper as I suspect they were using decimal places and I’m not). Still very impressive either way.

The AL position also resulted in fewer shocks required for patients who did achieve sinus rhythm.

What are the implications for EM practice?

This is a well designed trial with some robust results. As always there are issues we need to consider. The trial was not blinded to operators or patients and there are a number of exclusions in there. For EM clinicians we must be mindful that this is a different group of patients and we must be cautious about extrapolating this data to other conditions that we see such as VF/VT and different emergency patient groups. We must also point out that these are biphasic machines which are in common usage in the UK, but this may not be the case in low and middle income countries. The authors discuss past trials in the paper where an AP position appeared to be better for monophasic machines.

That said, for a procedure that is really a pathophysiological intervention that I imagine is mostly about the physics of energy flow then this paper reinforces my current practice of using AL pad positions for defibrillation in all cases. It probably also makes me less likely to consider changing pad positions as an early option in refractory VF/VT although I will retain that option for some cases.

The Bottom Line

For routine cardioversion the AL position should be used. For other forms of defibrillation the AL position is first choice, but the evidence for supporting this view is not as strong.

References

  1. Simon Carley, “JC: Should we rapidly cardiovert AF in the ED? St Emlyn’s,” in St.Emlyn’s, May 11, 2019, https://www.stemlynsblog.org/should-we-rapidly-cardiovert-af-in-the-ed-st-emlyns/.
  2. Pluymaekers NAHA, Dudink EAMP, Luermans JGLM, et al. Early or Delayed Cardioversion in Recent-Onset Atrial Fibrillation. N Engl J Med. April 2019:1499-1508. doi:10.1056/nejmoa1900353
  3. Anterior–Lateral Versus Anterior–Posterior Electrode Position for Cardioverting Atrial FibrillationAnders Sjørslev SchmidtKasper Glerup LauridsenDorthe Svenstrup MøllerPer Dahl ChristensenKaren Kaae DodtHans RickersBo Løfgren and Andi Eie Albertse https://www.ahajournals.org/doi/10.1161/CIRCULATIONAHA.121.056301
  4. Defibrillation pads and paddles https://litfl.com/defibrillation-pads-and-paddles/

3 thoughts on “JC: AP or AL position for cardioversion? St Emlyn’s”

  1. Great review Simon, thank you.

    A recent trial has shown starting with maximum energy levels to be superior to an escalating approach. This has now been included in the ESC guidelines from 2020.

    Do you think, given this trial was performed with escalating energy, this trial should be repeated? Interested to hear your thoughts on how using a fixed maximum protocol might affect the results.

  2. The reasoning for AP was that AP conducts current through the atria and is therefore more effective an AF. What could be an explanation that AL is superior to AP?

    1. Maybe that reasoning was just wrong. It’s very common for us to find that perfectly reasonable pathophysiological assumptions don’t work out in practice. This may just be another of those.

      S

Thanks so much for following. Viva la #FOAMed

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