Without evidence of benefit, an intervention should not be presumed to be beneficial or safe.

- Rogue Medic

Dead VT vs Not Quite Dead, Yet VT.

 

In my post The Three Flavors of VT (VT = Ventricular Tachycardia),[1] I described some of the problems we have when assessing death.

The heart can be beating so quickly that no palpable pulse is produced,, or it can be beating so slowly that no pulse is produced or it might not be beating at all.

The heart that is beating too quickly or beating too slowly is not stopped. This heart is producing so little output that the person assessing for a pulse is not able to feel a pulse.

The carotid artery is the place to assess for death.

So, there’s dead and there’s dead?

Let’s go back to ACLS class and listen in on some more bad teaching .

Are we going to take the Wayback Machine?

No.

During a scenario the student is presented with an unstable VT patient.
 

Student – I want to give this unstable VT patient some epinephrine.

Instructor – You killed him!

 

Gee. That’s one way to make sure they remember.

Depends on what you want them to remember and it is bad science.

What do you mean “bad science?”

Do you know of any controlled studies of patients being treated with epinephrine vs. placebo for unstable VT?

No.

Then how would you be able to say with any certainty what the result of such treatment would be?

Well, it is a good guess.

It may be a good guess, but it is not science and it is very bad teaching.

Why is it bad teaching?

It teaches that we know what will happen to the patient when we give a treatment.

We don’t.

But there are some treatments that we know will produce certain effects when we give them.

Even that is wrong. Most of the time the medication may produce the expected response, but not always.

To suggest otherwise is very bad medicine.

We have a good idea of what will happen when we give epinephrine to a patient with unstable VT.

Based on what?

Everyone knows that epi –

Stop! Sentences that start with “Everybody knows” often end with the speaker looking like a fool. When they do not, it may be because the audience is even more foolish than the speaker.

But epinephrine will cause the heart to beat too fast, and overstimulate the heart, and maybe cause the rhythm to change to V Fib (Ventricular Fibrillation).

Maybe it will overstimulate the heart.

Then you would be wrong to give epinephrine to VT.

What about when the pulse can no longer be felt?

Then you give epinephrine!

But the rhythm is still VT, just pulseless instead of unstable.

There is a big difference between a living patient with VT and a dead patient with VT.

The difference can be really very subtle.

With unstable VT someone is able to feel a pulse, so we know there is cardiac output.

With pulseless VT, someone is not able to feel a pulse, so we think that the cardiac output is much less.

What do you mean think? Pulseless means NO cardiac output.

No.

The heart can be beating, there is probably blood that is circulating due to the heart beating, but the amount circulating is so little that there is no palpable pulse.

The heart normally beats slowly enough that the ventricles fill completely before each beat. When the heart accelerates, the cardiac output increases, but only as long as the heart is able to keep filling up. Eventually the heart is beating so quickly that the heart does not have time to fill when the next contraction of the ventricles occurs. Since the heart is not full, the amount that leaves is less. The blood pressure will start to fall if this continues. If the heart keeps accelerating, eventually the blood pressure, or the work of the heart, or the filling of the coronary arteries, or something else will catch up with the patient and they will exhibit signs of being unstable. If the heart is beating even faster the pulse may disappear.

What was that about the coronary arteries?

They fill between heart beats, so as the heart beats faster – even though the heart is working harder – the ability of the heart to supply blood to itself decreases.

Ouch!

Do you remember our criteria for unstable tachycardias?

What were those criteria, again?

Acute altered mental status (not their normal level of consciousness).

Ongoing severe ischemic chest pain (not mild CP or palpitations).

Congestive heart failure (not just a previous diagnosis, but something that is causing real problems right now).

Hypotension (if hypotension is the only problem and they seem otherwise stable, I am not as aggressive as with the other criteria).

Or other signs of shock (not everything fits neatly into a list, this refers to things that activate the pucker factor).[2],[3]

 

But the pulseless patient is not like that – the pulseless patient is dead!

So the first category – acute altered mental status would not apply?

Yes, but this person is unresponsive.

Usually – and unresponsive is probably not their normal level of consciousness.

And the other categories do not apply.

Well the chest pain probably does not, but do you think the patient is hypotensive?

They don’t have a blood pressure!

No. The patient does not have a palpable pulse – that just means that the blood pressure is too low for the person attempting to measure the pulse to be able to feel enough evidence of the pulse.

But they aren’t showing signs of shock.

You’ve been watching too much TV. The signs of shock do not go away just because you can no longer feel a pulse.

OK. Let me see if I understand this. The patient just has less cardiac output when pulseless than when unstable. Isn’t that what I said before?

If the same person is attempting to feel the pulse, yes. You were generalizing that all pulseless patients would have lower blood pressures than all unstable patients. There is too much variability among patients to make any such broad statement.

Give me an example.

A well conditioned athlete may tolerate a heart rate of 200 for an extended period and never show signs of instability. Someone with heart problems may be pulseless with a rate of 200 showing on the heart monitor. One patient is exercising and the other is assessed as dead.

Or a person with a blood pressure of 70/38 may be stable, while another patient is unstable even with a much higher blood pressure.

But the dead guy with VT needs to get epinephrine to help his heart start beating again.

His heart appears to be beating – just much to quickly to produce a pulse.

Then epinephrine would not be a good idea?

Well, if the biggest difference between the two might be the ability of the person assessing for the presence of a pulse to feel a pulse, then we aren’t really treating a difference in the patients, but our ability to assess our patients.

How did Schroedinger’s Cat get in this conversation?

Why don’t we just leave the cat in a state of uncertainty, for now.

So, his heart is beating, just too quickly?

Probably. The heart may not be contracting at all, but still producing a VT-looking rhythm on the heart monitor.

But if his heart is beating, just much too quickly, how is this different from the unstable patient the instructor said would be killed with epinephrine?

Not very different at all. Depending on who is assessing the patient, it could be the same patient.

Then epinephrine could be the worst thing we could give the patient.

It could be.

Was the point of this to drive me crazy?

No, just to point out another reason why epinephrine in cardiac arrest[4] may not be such a great idea.

And the part where you drive me crazy is just a bonus?

🙂
 
See also –

Epinephrine in Cardiac Arrest

More on Epinephrine in Cardiac Arrest.

Footnotes:

[1] The Three Flavors of VT
Thu, 03 Apr 2008
Rogue Medic
Article

[2] Cardioversion – I’m not doing that, you do it!
Mon, 24 Mar 2008
Rogue Medic
Article

[3] Initial Evaluation and Treatment of Tachyarrhythmias
2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care
Part 7.3: Management of Symptomatic Bradycardia and Tachycardia
Tachycardia
Free Full Text from Circulation

[4] Epinephrine in Cardiac Arrest
Sun, 06 Apr 2008
Rogue Medic
Article

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Comments

  1. thanks for the mental cartwheels. . .one more cup of coffee and it will all make sense, i’m sure. Certainly a bit different perspective than the one I got yesterday in my ACLS recert class.

  2. It is my opinion that a better understanding of what is going on and where treatment might take the patient is essential to medical care.Too often we give drugs without considering the full effect the drug may have on the patient, the interactions with other drugs the patient may be using, the possible interference with longer term care in the hospital.Better numbers to write in the vital signs column does not necessarily mean a better outcome for the patient.Our whole reason for treating the patient is to improve the outcome for the patient.

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