February 2023

Clinical Question

AP or AL for transcutaneous pacing?

Title of Paper

Anteroposterior pacer pad position is better than anterolateral for transcutaneous cardiac pacing

Journal and Year

Resuscitation, 2022

Lead Author

Siamak Moayedi

Background

• You may be experiencing Deja Vu. In June 2022 we covered a paper comparing AP to AL placement for cardioversion of AF (spoiler alert, AL was superior)
• But no, this is looking at patients requiring pacing
• You’ll all have played with this in ALS scenarios. We use TCP for unstable bradycardia (when we can’t nurse them through it on drugs like isoprenaline) and as a bridge to transvenous pacing (either temporary or PPM)
• TCP can hurt, and unless your patient is unconscious I’m sure they’d appreciate being dealt the lowest energy necessary to get the job done
• Reported energy needed ranges from 40-130mA, average 80mA. If you were wondering.

Study Design

• Prospective crossover study

Patients Studied

• Patients undergoing elective cardioversion for atrial flutter or fibrillation

What They Did

• Immediately post cardioversion (200J sync shock)
• Pads removed and two new pacer pads placed (AP and AL)
• Randomly started with AP or AL depending on odd or even participant number
• Pacer set to 120% of patient’s resting rate
• Started at 40mA then increased 5mA per second until capture (sats probe HR same as set rate for 10 seconds)
• Repeat for other pad placement
• Record energy needed for each.
• Record amount of chest wall muscle contraction for each.

Outcomes

• Primary: capture threshold in the two positions
• Secondary: severity of muscle contractions (scale of 0-5 where 0 is none and 5 is both pecs dancing)

Summary of Results

• 20 participants enrolled,
  • 3 incomplete data (anaesthetist chickened out before second pacing position)
  • 4 didn’t capture
  • That left 13 with data to analyse

Primary: AP superior

• Mean AP capture 93mA
• Mean AL capture 126mA
• Difference 33mA favouring AP (p=0.0001, 95% CI 20-45)

Secondary: AL made chests twitchier – as you would expect with higher mAs

• AP chest wall contraction severity 3 [2-3] vs 4 [3-4]
• p<0.005

Authors Conclusion

The AP position requires, on average, 33mA less output to achieve pacing that the AL position for TCP. At least 20% of patients may not capture in either pacer pad position. Chest wall contractions are less severe when the pads are placed in an AP position compared to the AL position. Major resuscitation guidelines may consider favouring the AP position for transcutaneous cardiac pacing.

Clinical Bottom Line

Some limitations to consider:

• They were capturing elective patients who were in sinus rhythm, so not our unstable, bradycardic cohort with their variety of reasons for being slow
• Patients had just had a 200J shock, so what’s that done to the pacing threshold of the myocardium?

That being said, I can’t see a significant reason not to try AP in the first instance, unless you struggle to get the posterior pad on in an unstable patient.

Lower capture energy = less muscle contraction = more tolerable for the patient.

Note that 1/5 didn’t capture at all. That might be because they were in their own sinus rhythm, but it’s also a limitation of TCP in general. Pacing wire anyone?

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Clincial question

Where should we keep the BP in someone who has ROSC after cardiac arrest

Authors

Kjaergaar et al NEJM 2022

Background – we look after a lot of cardiac arrest patients. If you’ve made it to ROSC then the usual reason they end up dying is because of a poor neuro outcome. It’s hard to know what’s happening with cerebral autoregulation post cardiac arrest adn there was a thought that maybe we should treat them like TBI type patients where we typically target a higher MAP to account for high ICP. – these guys tested a fairly bacsic pragmatic question as to whether a higher MAP target resulted in better outcomes

Methods

– two centres in Denmark. randomised trial

– included adults who had ROSC but remained comatose after cardiac arrest with a presumed cardiac cause

– actually part of a complex trial called the BOX trial where they actually tested two things. This trial is the BP trial, the other one was a saturation target trial – they used fairly standard TTM at 36 degrees

– the cool bit about this trial is that they managed to blind it to everyone involved. They effectively hacked a bunch of philips monitors to display a BP that was either 10% lower or 10% higher than the actual BP. Clinicians in the trial where then told to target a MAP of 70 without knowing they were actually getting a MAP of 63 or in the other arm a MAP of 77

– outcome here was death of any cause mixed with CPC. Now this seems like a fudge having a composite but basically it’s not far off the beloved mRS that is used in all the stroke trials.

– powered to look for a 10% absolute motality difference. They seems to have neutral prior bias in that they didn’t have a clear stance on which they thought would be better – the higher or the lower BP Results

– 800 pts which met their target enrolment – they achieved lovely separation between the two BP graphs

– they ended up finding 34% vs 32% mortality favouring the lower BP group which is right in the middle of expected mortality and of course the tiny 2% difference here is more likely noise than true difference.

– they have a nice forest plot of all the outcomes and they all have CI that straddle either side of the line of the no effect Thoughts – chose this largely because of the blinding. I thought it was well done and eliminates any claims of bias that you might make.

– in this large very pragmatic population of all comers it makes no difference so i’ll probably stick to my 60-65. – But like all these large pragmatic trials you may find patients yuo might want to pursue higher targets in and no doubt there are sub groups that are still worth studying.

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