transcutaneous pacing??? questions from the curious and uneducated

[stoic]

what's up guys -

i've got a few random questions about transcutaneous pacing. this stuff is probably pretty simple to you guys, but i'm still a youngin'.... so humor me?

first of all, how much energy is used during each "shock"? 50 Joules? more? less?

next, is the electric shock conducted through the normal conduction pathways? or does it act diffusely and non-specifically?

(sort of a tie in with the previous question) are the atria and ventricles paced independantly? does this depend on the cause of the dysrythmia (IE only pacing the ventricle in the case of a severe branch block)?

is transcuatneous pacing a purely supportive measure or can it be used to restore a NSR? and if it can, how is this different than defibrilation?

alright, that's it for now. thanks for the knowledge.

S

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[leviathan]

what's up guys -

i've got a few random questions about transcutaneous pacing. this stuff is probably pretty simple to you guys, but i'm still a youngin'.... so humor me?

first of all, how much energy is used during each "shock"? 50 Joules? more? less?

next, is the electric shock conducted through the normal conduction pathways? or does it act diffusely and non-specifically?

(sort of a tie in with the previous question) are the atria and ventricles paced independantly? does this depend on the cause of the dysrythmia (IE only pacing the ventricle in the case of a severe branch block)?

is transcuatneous pacing a purely supportive measure or can it be used to restore a NSR? and if it can, how is this different than defibrilation?

alright, that's it for now. thanks for the knowledge.

S

Hey stoic,

This is a good question and I'm interested to know as well. I'm not sure if this is correct, but I think transcutaneous pacing is just going to be a diffuse depolarization, and there isn't going to be any ability to independently stimulate the atria or ventricles. The difference between defibrillation and TCP is that the former is to revert VF or PVT back to a functional rhyhtm, and the latter is to attempt a more stable rhythtm in someone who is bradycardic, or attempt to produce a perfusing rhythm during aystole.

 

[southerndoc]

The ACLS algorithm recommends that for patients with a pulse who are just bradycardic, you start at the lowest setting (1 mAmp) and increase until you get capture. Then increase by 10% more.

For patients without a pulse (i.e., asystole), the recommendation is to start at the highest level and then decrease it until you lose capture. Then increase it until you regain capture.

I can't say that I've seen any recommendations in joules.

 

[stoic]

The ACLS algorithm recommends that for patients with a pulse who are just bradycardic, you start at the lowest setting (1 mAmp) and increase until you get capture. Then increase by 10% more.

For patients without a pulse (i.e., asystole), the recommendation is to start at the highest level and then decrease it until you lose capture. Then increase it until you regain capture.

I can't say that I've seen any recommendations in joules.

what are the indications for TC pacing of a bradycardic patient as opposed to atropine? why is one better than the other?

 

[leviathan]

what are the indications for TC pacing of a bradycardic patient as opposed to atropine? why is one better than the other?

My guesses: If you max out on atropine, or it doesn't have an effect then you might want to pace. If the patient has a 3rd degree heart block, atropine won't have any effect as it works at the AV node, so there's another reason. I've done some ACLS, but that's about it, so this is all speculation.

 

[Seaglass]

What SouthernDoc and leviathan said. The energy is measured in milliamps (current) rather than joules (work).

It acts diffusely, you should see a wide QRS on the monitor

You cannot pace the atria and ventricles independantly by TC pacing

It is usually a supportive measure and is really only indicated in the bradycardia ACLS algorithm when atropine fails but I have seen it used in PEA quite a bit. Often you get electrical capture (QRS on the monitor) but no mechanical capture (no cardiac motion on US)

 

[OSUdoc08]

what are the indications for TC pacing of a bradycardic patient as opposed to atropine? why is one better than the other?

If the patient is unconscious or you don't have IV access and the patient is unstable, TCP is essential. If the patient is talking to you, Atropine is likely the way to go.

Also, Atropine may not work if the cause for Bradycardia is not related to Vagal stimulation.

As written above, pacing is in mA. There is no "shock" with voltage. The rate is set in a normal range.

In a pulseless, apneic patient found early in asystole, TCP is the intervention of choice before medication administration.

 

[southerndoc]

what are the indications for TC pacing of a bradycardic patient as opposed to atropine? why is one better than the other?

Transcutaneous pacing is a class I intervention in bradycardic patients. Atropine is a class IIa. TCP is ALWAYS indicated if you want to do it. It's always better than atropine. However, most people try atropine first since TCP can be quite painful, requires sedation, etc.

Atropine should NOT be used in 2nd degree type II or 3rd degree heart blocks. For those rhythms, it is best to go straight to TCP. For other bradycardias, a trial of atropine can be done or you can go straight to pacing.

For cardiac arrest patients, transcutaneous pacing is indicated EARLY in asystole. This doesn't mean intubate the patient, give an epi, give an atropine, give another epi, continue CPR, and then go "oh, let's try to pace the patient." That annoys the crap out of me. TCP is indicated IMMEDIATELY in asystole patients. Either try it early, or don't try it at all. In other words, try it before you intubate the patient!

 

[leviathan]

For cardiac arrest patients, transcutaneous pacing is indicated EARLY in asystole. This doesn't mean intubate the patient, give an epi, give an atropine, give another epi, continue CPR, and then go "oh, let's try to pace the patient." That annoys the crap out of me. TCP is indicated IMMEDIATELY in asystole patients. Either try it early, or don't try it at all. In other words, try it before you intubate the patient!

Nice. It's also indicated first in the asystole mnemonic "Check me in another lead, then let's have a cup of TEA" where T = transcutaneous pacing, followed by epi and atropine.

 

[Doczilla]

Transcutaneous pacing delivers the same DC shock as a monophasic defibrillator, but at about 1/1000th of the energy. With defibrillation, the point is to depolarize the entire myocardium simultaneously and allow the heart to restart itself in an organized fashion. TCP needs only to deliver enough energy to depolarize a couple of cells in the ventricles, at which point the depolarization will spread to adjacent cells and cause a contraction. It is usually a bridge to placement of a transvenous pacemaker and correction of the underlying cause of the heart block (ischemia, certain overdoses, etc.)

Many modern defibrillators are biphasic, meaning that the shock travels one direction and then the other. This is not similar to the shock delivered by the pacer.

Atropine should NOT be used in 2nd degree type II or 3rd degree heart blocks. For those rhythms, it is best to go straight to TCP. For other bradycardias, a trial of atropine can be done or you can go straight to pacing.

Atropine is indicated in 2nd or 3rd degree block caused by digoxin toxicity. Digoxin may cause bradycardia and heart block through a) stimulation of the vagus nerve, b) sensitization of baroreceptors, and c) fascilitation of muscarinic transmission at the AV node. These result in increased parasympathetic tone at the AV node which may be reversible with atropine. To complicate matters, transcutaneous pacing in dig toxicity is hazardous as it can cause arrhythmia.

Most episodes of AV block are not caused by dig toxicity, but I don't see any harm in giving a trial of atropine as you are setting up the pacer.

Pacing in bradycardia (with pulse) depends largely on clinical judgement. How symptomatic are they, and how well will they tolerate the atropine? TCP is extremely uncomfortable and will require sedation and analgesia. Atropine is easier to administer, and though not without side effects, is better tolerated than pacing.

Southerndoc is absolutely right about pacing early in cardiac arrest. Unfortunately, most people only think of it 20 minutes into the code. At that point, the ATP is used up in the heart muscle, so pacing won't help. The ideal situation for pacing in asystole is for witnessed asystole, such as which may result after a defibrillation. In that case, reach straight for the pacer controls.

'zilla
ACLS-EP-Inst

 

[southerndoc]

Atropine is indicated in 2nd or 3rd degree block caused by digoxin toxicity. Digoxin may cause bradycardia and heart block through a) stimulation of the vagus nerve, b) sensitization of baroreceptors, and c) fascilitation of muscarinic transmission at the AV node. These result in increased parasympathetic tone at the AV node which may be reversible with atropine. To complicate matters, transcutaneous pacing in dig toxicity is hazardous as it can cause arrhythmia.

Good point!

Most episodes of AV block are not caused by dig toxicity, but I don't see any harm in giving a trial of atropine as you are setting up the pacer.

In general, atropine is highly unlikely to work in 2nd degree type II and 3rd degree heart block because 2nd degree type II and 3rd degree heart block are AV dissociation problems and not vagal stimulation or sinoatrial nodal problems. In fact, many of these rhythms will have atrial rates in the 60-70 range, but ventricular rates that are profoundly bradycardic.

It is for this reason that TCP should be the primary treatment of these bradycardic rhythms. Atropine is unlikely to work, and although you say it won't hurt, I think your time could be better spent by administering sedation instead of atropine. There are some reports that atropine administration with high-degree heart blocks can be harmful.

While we are pointing out when not to use atropine, one should also remind us of what all of us already know: atropine is contraindicated in transplant patients with denervated hearts. Atropine can have a paradoxical response and induce asystole in denervated hearts.

 

[stoic]

hey guys -

thanks so much for the responses. i really appriciate it.

thanks again,
s