00:01
Thad Wilson: Now let's talk a little bit about atrial
systole.
00:04
We kind of ended on it being the last little
kick of
volume into the left ventricle.
00:11
It's initiated by the p wave from the ECG.
00:15
It occurs again right at the end of
ventricular
diastole. We talked about it also
producing a little bit of pressure on its
own.
00:27
The pressure that it induces involves
squeezing in on the blood that's there
right at the end. And that, again, normally
pushes about 10%
into the left ventricle to cause the full
filling.
00:41
So someone really doesn't need to have a lot
of atrial
systole under most circumstances.
00:49
In fact, you could have a cardiac arrhythmia
known
as atrial fibrillation, in which the atrium
really don't contribute
much to ventricular filling.
01:01
And you could be walking around and you
might not even know that person has this
arrhythmia. On time, though, when atrial
systole becomes very
important, aren't things like during
exercise, where you have large volumes of
blood coming back to the heart?
And the top part can help squeeze that blood
into the left ventricle
so that you can get a better contraction
out.
01:24
Because that way you can utilize the
frank-starling mechanism to push
more fluid out per stroke without utilizing
any more energy.
01:34
Atrial diastole occurs after atrial systole.
01:39
Remember that this atrial kick is what
creates the A wave.
01:44
However, during the distal portion of the
atria these are phases
two through seven.
01:50
There are two other waves we need to be
concerned about.
01:53
The first of these is known as the C wave.
01:57
The C wave occurs during the contraction of
the ventricles.
02:01
This is actually a pressure reverberation
that occurs.
02:06
It either occurs during phase two, as shown
in the graph,
or sometimes even a little bit into phase
three.
02:14
The other way we need to be concerned about
is the v wave.
02:18
The v wave occurs after you start to get
blood filling the
atria. It continues to fill the atria until
suddenly the
AV valves open and there is a sudden
pressure fall
that's known as the V wave.
02:35
So in terms of the atrial filling pressures
and the atrial
contraction pressures, we can look at a C
and V being those
items that we want to make sure we have a
good feeling for why they are occurring.