[LuvbabiesRN]

Does anyone have an easy way to explain the basics of temporary epicardial pacing... As part of my new grad internship i just had an all day class about pacemakers.... and i still don't get it... I am mostly concerned with the temporary ones that they put in post -op open heart surgery patients... I think i understand the VVI, DDD, VOO, DVI stuff but what what i dont get is how you set thresholds.. like sensing thresh holds and pacing thresh hold... We had temporary pacermakers and we were playing with all the buttons and trying to set thresh holds and stuff but i just dont get it.... Anybodys easier explanations would be greatly appreciated!!! Thanks!!!

[Jill - Pa]

First try:
http://www.icufaqs.org/Pacemakers.doc

A lot of it becomes clear when you actually get your hands on one and can play with it while it is connected to an actual person.

A mneumonic I developed when trying to determine what wire goes where when in an emergency and need to connect someone's epicardial wires to a pulse generator:
BLS as in Basic Life Support.
The 'L'onger wire is the 'S'kin wire and goes into the 'B'lack port.

[RNMBA]

The easiest way to set thresholds is to start low and increase the MA until you get consistent capture.

Patients capture at different strengths due to individual differences as well as placement by the surgeon. You'll even occasionally get some that capture with reversed polarity and others that won't capture at all.

[LuvbabiesRN]

Hey thanks for your imput JIll-Pa.. that website was helpful!!!

[LuvbabiesRN]

OOPs that was supposed to say input..

[XIGRIS]

Here are some tricks or should I say some footnotes on epicardial pacers. Pacemakers are sometimes hard to understand but I tried to make it a little bit simple for my students. Here it goes.

I would just like to emphasize the two most common problems with any pacemakers well here lets just say epicardial pacers which we commonly see with CABG patients.

1. Failure to capture
2. Failure to sense


FAILURE TO CAPTURE.
Remember this, the higher the number example 10 or 15 ma, the higher the power or the more you capture. Most surgeons leave their ma to 10 so if you do not have capture meaning ....

if the pacer is on VVI mode... you do not have a QRS after the pacer spikes then you increase the number of your output. Go as high as you can until you get the QRS complex.
this is also true if the pacer is supposed to capture te Atrium like when it is in AAO mode. Meaning there should be a P wave after the pacer spike, if there is none then by all means go up on your output ( the ma) higher.

In the case of a trnascutaneous pacemaker, the one you have on your crash carts, the output is way higher than 20 ( 20 ma is mostly the highest output in a generator ), most of the time it is 60 or 70. Why? Because the current has to travel thru your skin and ribs in order for it to stimulate the heart.

FAILURE TO SENSE.
Just an example in VVI, the sensing chamber is the ventricle. Hence, the pacemaker should sense the ventricle before it fires.
If you see a spike somewhere near the P wave or after the ORS or even worst near the T wave, then you are not sensing. So what you need to do is....

Increase your sensitivity by ok remember this going down in your mv. So if it is set at 2.0, inorder to increase your sensitivity ( meaning in order for your pacemaker generator to be sensitive to the Ventricle in the case of VVI), you go dowm to 1.5. The lower the number in your sensitivity threshold the move sensitive you are.

This is the same as in AAO. the generatior shoild sense the P wave but if you see spikes all over like near the QRS, after the P wave or near the T wave, then you are not sensing right. Go down your number.

To recap...

1. THE HIGHER THE NUMBER IN YOUR OUTPUT THE MORE POWERFUL THE GENERATOR IS, HENCE THE MORE CAPTURE.

2. THE LOWER THE NUMBER IN YOUR SENSITIVITY THRESHOLD, THE MORE SENSITIVE YOU ARE.

FYI:

The most fatal between a. failure to capture and b. failure to sense?
Answer. B. Failure to sense.
Why? If your pacemaker is not sensing the right chamber, it will trhow spikes all over the place. And if it hits the Twave ( most vulnerable part in your cardiac cycle ) it can trigger R on T phenomenon which is the adoring, and I call it the ooohhh ohhh ohh rhythm ( because once you see it on your monitor you cant say its name instead you say ohooo ooohhh ohhhh and then you run in the room with a crash cart ) Torsades de Pointes.


Hope this help.

[XIGRIS]

I forgot to add this yesterday.

When two pacer wires come out of the patient, it does not matter which is (-) or (+). Just hooked them in your generator.
If only one pacer wire, the wire that comes out of the patient is the negative pole and then you have to find you a cable to be your positive pole ( ground ) and attach it to the skin. Any place in your body that has skin.

Just FYI. In case of emergency, when you need to hook your pacer wires to the generator and still you do not get adequate capture ( meaning no QRS or P wave depending on the pacer mode ) go to as high as 20ma. And if it still not capturing, flip the the wires and switch it to different poles.