1.0 What is fibrillation?
Fibrillation is an
arrhythmia that affects either the atria as a pair, or the ventricles as a
pair, producing “a-fib”, or “v-fib”, respectively. Most
cardiac rhythms are organized – they’re regular in some way, producing some
sort of regular (as opposed to disorganized), rhythmic motion of the chambers,
hopefully producing a blood pressure. In fibrillation, the cardiac tissue of
the chambers involved wiggles about like (classic phrase) “a bag of worms”.
Does a chamber wiggling like a bag of worms pump any blood, produce a cardiac
output, eject any fraction of its contents? No, it does not!
As I always try to
point out, all the waves that you see on ECG strips actually represent some
kind of physical motion of one or the other set of cardiac chambers, and the
trick is to try to visualize what those chambers are doing in any given rhythm
situation. Let’s see if a quick review of some strips helps the visualization
process.
Here we are familiar Sinus rhythm on image 01. Organized, rhythmic, producing stable contraction of
the chambers – first the atria, then the ventricles. So nice orderly
motion, first above, then below.
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| Image 01 |
Next slide (Image ) atrial flutter. Still organized: the atria are
contracting rapidly, sure, at about 300 bpm, and the ventricles are responding
to every third or fourth impulse, slowly enough that the ventricular chambers
have time to fill up nicely between beats, fast enough to probably maintain a
good blood pressure. So I visualize the atria clipping along, with the
ventricles contracting every third or fourth time.
 |
| Image 02 |
This one? Well – is it organized? Actually it is: see
the pattern of doubles? It’s a little easier to figure out by looking at the
lower part of the strip – this is a sinus rhythm, and after every sinus beat
comes a PAC, followed by a compensatory pause. So yes, still organized.
“Regularly irregular”.
 | |
| Image 03 |
How about this one? , VT. Ugly, scary, but still organized, regular – the chambers (which ones?)
are moving in a steady manner. On your mental screen you should see the ventricular
walls contracting very rapidly – do they have time to fill? Should we shock
this rhythm? It depends…
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| Image 04 |
1-1: What is
atrial fibrillation?
How about this one?
Not organized? Should we shock this rhythm? A-fib for sure can be a shock able
rhythm, but look at the QRS rate – in the 70’s. What would have to be happening
to make this a shock able situation? What do you visualize here? Atria: bag of
worms. Ventricles – occasional, but normally conducted QRS’s. Are they too slow
or too fast to make a blood pressure? How do you tell?
 | |
| Image 05 |
1-2: What
is ventricular fibrillation?
Here’s an ugly one
- you probably recognize this one right off. Doesn’t look organized to me! What
rhythm is this? Visualize the ventricles – everybody see the worms? What should
we do?
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| Image 06 |
2- What is De-fibrillation?
So:
all set on organized, and not organized? The treatment for nasty arrhythmia is
often electrical, right? The point is: one type of treatment: cardioversion - is
for the organized kind of rhythm, and the other is, De-fibrillation
is for disorganized rhythms.
What
you want to do is to send a fixed amount of electrical energy along the normal
conduction path of the heart: along the Lead II pathway.
| Image 07 |
Here’s a diagram of
the normal lead II: the positive
electrode is down near the apex of the ventricles, the negative one is at the
atrial end. Everybody remembers that the normal direction that the cardiac
impulse takes is from the SA node at the northwest corner, up near Oregon, down
and towards the southeast in Florida, where the positive electrode lives? And
that the signal moves along the pathway as the cells depolarize, in sequence,
along that pathway?
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