# Anterior Lateral vs Anterior Posterior Pacer Pads



## wanderingmedic (Aug 21, 2014)

Anyone ever find that anterior posterior positioning for transcutaneous pacing pads works better than the anterior lateral position? In school I was taught to use the anterior posterior position, but my current protocols do not specify pacer pad positioning. 

Does anyone use the anterior posterior positioning as their first choice for defibrillation?


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## Jason (Aug 21, 2014)

I use anterior/posterior pad placement, for pacing, cardioverting, and defibrilation.  Key about pad placement is to have the heart between the pads, as in a straight line from pad to pad with the heart on the line between the pads.  Sounds easy, but many times this is not done properly.  Also, the anterior/posterior placements give maximum conduction and shortest distance, for cardiac treatment (in most patients).


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## Christopher (Aug 21, 2014)

That video does not feature capture. They've also placed the wrong pad on the anterior aspect.


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## Jason (Aug 21, 2014)

The video also shows poor pad placement for optimal treatment.  For pacing or defribrilating the anterior pad should be more over the apex of the heart. In the video it looks more over the base.


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## OnceAnEMT (Aug 21, 2014)

The manufacturer's instructions on the pads we use in the ED I am at recommend anterior-posterior placement for pacing, but it works either way.

Placement in this video is definitely awkward. The pictures on the pads and packaging are there for a reason. Personally I put the anterior pad somewhere between sternum and just offset the sternum, as far left as the anatomy will allow. Then the posterior pad is just offset left of the spine, slightly off the inferior aspect of the scapula.


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## sdadam (Aug 30, 2014)

I'm pasting a response I wrote long ago to a post on Dextrocardia as the discussion of pad placement is obviously applicable in these patients. TL;DR would be we should all be using anterior / posterior placement unless there is a physical reason or it would significantly delay electrical intervention. Let me know if you have any questions. 
___________________________________

Dextrocardia can be one of a few types...

Dextrocardia (dextroposition) alone means that the heart is more on the right side of the thorax than the left, but does not necessarily mean that it is anatomically reversed.

Dextrocardia Situs Inversus, on the other hand means a true mirrored reversal of the normal anatomical position of the heart. Identified on an EKG most commonly as an extreme right axis deviation, positive deflection of the QRS in aVR, and reversed precordial QRS amplitude progression. 

Two best differentials: limb lead reversal (LLR) or Dextrocardia (which do you think is more common). In Dextrocardia you will have inverse R waves, not so much with LLR, also Dextrocardia will have loss of voltage across the myocardium, LLR will not.

Finally it is worth mentioning Dextrocardia Situs Inversus Totalis in which all of the major organs of are in mirrored positions.

I think most of that was talked about in the article that you referenced, so about your questions.

If you have a PT which you are certain is a Dextrocardia Situs Inversus PT, then yes, you should both reverse your ECG leads and defibrillation pads.

This question really comes down to the much debated question of "How important is pad placement". And most research shows that it is actually quite important.

When defibrillating a PT, only a fraction of the energy delivered to the body actually transverses the myocardium. Ideal placement of electrodes for defibrillation and pacing is the anterior/posterior model (not the more commonly used upper right, lower left anterior model) this has to do with the fact that defibrillation is not accomplished with Joules.

I know, I know, we set Joules and then press shock. The truth of it is defibrillation is accomplished with CURRENT. An adequate amount of current must pass through the actual myocardium depolarizing a critical mass of it.

Energy (in Joules (J)) = Voltage * Current * Time

And 

Voltage = Current / Impedance

Modern defibrillators Lifepack and Zoll, both are able to read impedance of the patient in order to deliver the most effective energy amount possible, they cannot however direct the current through the myocardium, that is up to YOUR pad placement!

Soooooo, we can see that there is no real way to decide the energy (J) delivered since we have no control over the impedance presented by the PT, The monitor makes it's best guess, usually rated +/- 5%, up to 50 Ohms of impedance (for Zoll).

Taking this all back to your PT with Dextrocardia, if you don't switch the pads can defibrillation still work?

Of course, you are just decreasing the CURRENT across the myocardium, so it is beneficial to mirror your pad placement. 

You might even decrease impedance with poor pad placement but send the current through more non-cardiac tissue than you will with proper pad placement. Our goal is not Joules delivered to the PT, but Current across myocardium. 

Note we don't SWITCH pad placement we mirror it, meaning you should have a pad on the left mid-clavicular and a pad on the right mid or anterior axilla, NOT the positive pad on the bottom and the negative pad on the top (Really you should stick with anterior/posterior placement, and just move to the right side of the chest and back instead of the left, but for some reason no one does this unless pacing, at least in San Diego)

Long story short, mirroring your pad placement in a patient with Dextrocardia will allow you to maximize CURRENT that actually transverses the myocardium, which is your money when it comes to being successful in restoring an organized rhythm.

HOWEVER, if you have a patient in vTach or vFib, there is no criteria for defining Dextrocardia. So if you don't know you don't know, no big deal.

Hope that helped clear things up for you brother!

Adam

P.S. There is some small observational research out there which suggests that in difficult to defibrillate vTach or vFib, which persists in a "viable" manner (i.e. not super fine vFib) reversal of the pads can sometimes prove effective in restoring an organized rhythm. (NOTE now I'm talking about switching the positive and negative electrodes, not mirroring placement from left to right).

The idea being that when shocking the heart TIME was just as important as voltage and current in the above equation. Research identified that 10ms was the best time, with defibrillation threshold initially dropping and then increasing after passing the 10ms mark. Zoll monitors are biphasic and shock from one direction for 6ms, then reverse to the opposite direction for the last 4ms. So you are changing the nature of the waveform by reversing the pads. (I don't know about the Lifepack waveform but I'd bet it's the same)

I'm not saying it will work, but if you are a few 360j shocks in and keep getting vTach, you need to try something different, at least try moving your pads to maximize current across the myocardium, and try reversing them.

Doing the exact same thing over and over again expecting something different is crazy right!?

So now you can do it, and if anyone asks just start talking to them about current across critical mass of myocardium, and they will stop listening and let you do whatever you want.

Hope that was interesting too!


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