Shockable Rhythms

While on the topic, here's a question for the band:

What would happen if a defibrillation shock were given to a healthy, perfusing normal sinus rhythm?
 
Not to mention one sore and pissed off pt. when they came to again... ^_^
 
So what are we talking about here -- you'd lose a pulse with the first shock, then just restore it with another?

The reason this is a little confusing is because of the seeming conflict between two things we're taught --

1. Electricity through the heart (e.g. an accidental shock) can cause cardiac arrest, which is a problem

2. Defibrillation (i.e. electricity through the heart), when all goes well, causes the heart to stop beating and then spontaneously reset into a functioning rhythm

Why would the latter "reset" not occur after a shock to a normal rhythm?
 
It may happen that way but you could also shock them in to another rhythm. Also when you defib someone who is in VF/VT to "reset" the heart, it doesn't guarantee their heart will start again in a normal sinus rhythm and quite often it doesn't?
 
Brandon Oto said:
So what are we talking about here -- you'd lose a pulse with the first shock, then just restore it with another?

The reason this is a little confusing is because of the seeming conflict between two things we're taught --

1. Electricity through the heart (e.g. an accidental shock) can cause cardiac arrest, which is a problem

2. Defibrillation (i.e. electricity through the heart), when all goes well, causes the heart to stop beating and then spontaneously reset into a functioning rhythm

Why would the latter "reset" not occur after a shock to a normal rhythm?
Click to expand...
The problem with #1 is the possibility that you deliver electricity right on the T wave and you can put the heart right into VTach or VFib... both can be lethal arrythmias. If you delivery that shock just about any other time in the conduction cycle, all you do is cause the heart to depolarize or remain depolarized a little while longer. Normally the SA node will pick back up without too much of a problem... but it's that essentially R on T that you REALLY want to avoid.
 
Ahhh, thanks Akula.

So even in the case of an untimed shock through a healthy heart (oops, that cable was live?), arrest will only occur if you're unlucky enough that it hits you right during the T wave? Otherwise, no problem? (Although I guess with high enough voltage you might see significant trauma to the tissues anyway.)
 
Brandon Oto said:
Ahhh, thanks Akula.

So even in the case of an untimed shock through a healthy heart (oops, that cable was live?), arrest will only occur if you're unlucky enough that it hits you right during the T wave? Otherwise, no problem? (Although I guess with high enough voltage you might see significant trauma to the tissues anyway.)
Click to expand...
If you receive the shock that passed through the cardiac muscle basically beween the R wave and the 1st half of the T wave (absolute refractory period) you won't see another depolarization event... the cells can't fire again. It's at the beginning of the relative refractory period that you'd see that problem...

As to the other problem... it's not so much the voltage that causes tissue damage... it's the current. Think in terms of Watts... The higher voltage allows the energy to penetrate skin... but it's the amps that do the damage. The result is a pretty high wattage running through the body. You'll see the damage where the current flowed through the body...
 
How about if the shock lasts longer than a single cycle -- such as an accidental electrocution over a few seconds? Then are we sure to see an arrhythmia?
 
Brandon Oto said:
How about if the shock lasts longer than a single cycle -- such as an accidental electrocution over a few seconds? Then are we sure to see an arrhythmia?
Click to expand...
I would figure that the arrythmia would be one of 3... asystole, VTach, or VFib... in that scenario... assuming, of course, that the current passes through the heart in it's course from source to ground, and that the current seen by the heart is sufficient to cause depolarization. If it does, you'd see myocardial tetany until the current stops going through the body.
 
Brandon Oto said:
While on the topic, here's a question for the band:

What would happen if a defibrillation shock were given to a healthy, perfusing normal sinus rhythm?
Click to expand...

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=105x4640694

Some will remember of the idiot EMT that was playing around with the defib unit and shocked his partner killing her. He was convicted and now is serving prison time as her kids are without a mother.

So yes, electricity in the hands of unqualified people is dangerous.

R/r 911
 
Er... thanks Rid. I guess.
 
Ridryder911 said:
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=105x4640694

Some will remember of the idiot EMT that was playing around with the defib unit and shocked his partner killing her. He was convicted and now is serving prison time as her kids are without a mother.

So yes, electricity in the hands of unqualified people is dangerous.

R/r 911
Click to expand...

This is why basics shouldn't play with the monitor. I wonder how many joules he had it set to.

Jackass
 
Dominion said:
I'm curious about this, I've seen and heard different things. I've heard the above from an instructor during our cardiology/ACLS sections. I've seen other medics say it, I've seen cautions such as administer only if cardioversion is immediately available. I have also seen no cautions or warnings and have the "In presence of SVT, administer Adenocard unless patient is unstable or poor perfusion in which case perform immediate cardioversion."

What is the proper answer? Per protocol? My nursing drug reference, flip book, state protocols, epocrates, and drug packet do not even mention WPW.
Click to expand...

The problem with giving any medication that slows AV conduction (specifically a Calcium blocker like Cardizem) to someone with WPW is that you risk a paradoxical increase in conduction through the accessory pathway (WPW is, by definition, an accessory pathway conduction). When you slow the influx of calcium to the smooth muscle you cause vasidilation, the body then produces a sympathetic nervous response, which will follow the accessory pathway (which is the root of the original problem), thus increasing the rate of the tachycardia.

There is some controversy in using Adenocard for WPW in that any time you slow AV conduction while there is already an active accessory pathway, you make your accessory pathway all the more attractive. My personal take is that if syncronized cardioversion is available (which it will likely be, considering you have your patient on a monitor to diagnose the WPW), use it. If they patient isn't falling to pieces in front of your face (and is hemodynamically stable), give them an amnestic/anxiolytic first.

Linuss said:
And besides the fact that cardioverting already basically IS defibrillating, with minor differences (well... a few hundred joules minor :) )
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Remember, all defibrillations are cardioversions, not all cardioversions are defibrillations. Perhaps it's only a semantic difference, but it seems to be causing some confusion. What we term defibrillation is simply "unsyncronized cardioversion" and what's being referred to in this thread as cardioversion is "syncronized cardioversion". The number of joules is irrelevent. I can defibrillate a 25kg child at 50j or syncronized cardiovert a rapid a-fib at 50j. I can also defibrillate an adult at 200j or I can syncronized cardiovert them at 200j. One is a defibrillation, one is not.
 
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