Hi, welcome to our electrocardiogram video series.
In this one, we're going
to talk about sinus rhythm.
So far, we've covered the
components of the ECG paper
and broken down the cardiac cycle to see
how each phase is reflected as a wave.
We also went through the seven basic
steps to analyzing any ECG strip.
Now we're going to put that to the test.
ECGs come in many different forms
depending on the health of each patient.
By the end of this course, you'll
be able to identify most of them.
However, before you start diving
into the world of pathology,
you have to have a good grasp on the basics.
You can't recognize sick if you don't
know what healthy looks like first.
So let's take a look at a
normal sinus rhythm ECG strip.
Let's take another look at our beating
heart here and do a brief recap on the waves
and intervals of an ECG strip.
Remember, the electrical impulse
travels from the atria to the ventricles
and its pathway an influence on the heart
muscle is what's reflected on the ECG strip.
Now the impulse originates in
the sinus or the sinoatrial
or here's a third name, the SA
node - they all mean the same.
It travels from the SA node
through the left and right atria,
causing their contraction which is
reflected in the ECG as the p wave.
The impulse then heads through to the AV
node, but it doesn't just pass through.
It gets delayed or slowed down.
This delay is documented in the
ECG strip as the PR segment.
Next, we have the QRS complex, which
represents ventricular contraction.
This contraction is caused by the
impulse entering the ventricles
and dispersing through the Purkinje fibers.
The next wave is the T wave, which
is caused by the repolarization
or relaxation of the ventricles.
This period of time or interval between
ventricular depolarization and repolarization,
is represented as the ST segment in an ECG.
Finally, we have the U wave, which actually
may or may not be present on the ECG strip.
Although we don't exactly know what causes it,
it's believed to be the result of a delayed
repolarization of the Purkinje fibers.
So let's do a quick review
of how to analyze any strip.
Step one, you will analyze
the heart rate and rhythm.
Remember, you're making sure that
you have the same equal distance
between the R waves of the QRS, and the p waves.
So they should plot along equally,
p wave to p wave to p wave,
r wave to r wave to r wave.
The next step is to analyze the P waves.
You should have one P wave for every QRS.
They should all look the same and
they should measure out equally.
Third step is to measure the PR interval.
You measure from right where that P wave
starts to leave the isoelectric line
down to where it starts to dip down
again, that is the PR interval.
Now, step four is measure the QRS duration.
So you're going to measure how wide the QRS is.
Step five, take a look at the ST segment.
Step six. Look at the T wave, we want to
make sure that isn't depressed or elevated.
And then step seven, we're going
to measure the QT interval.
Now a normal P wave is the
atrial contraction precedes
every QRS complex in a normal sinus rhythm.
The rhythm is regular, but can vary slightly
during respirations, and
that is completely normal.
The rate ranges between 60 and 100.
Anything below 60 is sinus brady.
Anything above 100 is sinus tachycardia.
Now the P wave is positive in I and II.
Now it's little biphasic in lead V1.
But remember, there's a potential
of a patient is having problems,
we want to really good detailed look at
the electrical activity in the heart,
we'll use a 12-lead.
So those are just referring
to different types of leads.
If a patient is in the hospital, they're most
likely just on 5-leads for regular monitoring.
But if we do a 12-lead ECG, that's when we
suspect there might be a bigger problem.
So when we say the P wave is positive, that
means it's up above that isoelectric line
It is positive in lead I, lead
II and biphasic in lead V1.
So let's do it, let's dive in and hit
the seven steps with this ECG strip.
So first, let's assess the heart rate and rhythm.
Now if you count these up, we have a rate of 80.
Normal sinus rhythm is between
60 and 100, so we're spot on.
Look at the rhythm. Is it regular?
Well, measuring the distance
between the QRS complexes,
yeah, it plots right along, it's regular.
And you measure between the P waves.
Yeah, it's regular.
This is what we would expect
to see in a sinus rhythm.
So let me show you right where we looked here.
We're going to analyze the P waves in step two.
So see those blue boxes that have appeared?
That's to remind you of what the P waves are.
Now look, there is one P wave is present for
each of the QRSs, and they all look the same.
They don't just want to glance at that.
You really want to be disciplined
to look at each P wave,
make sure that it's there for every QRS.
Right, and then step back, and make
sure those P waves all look similar.
Step three, measure the PR interval.
Now take a look at the strip we've provided.
You're going to measure from where
the P wave starts to the R wave.
Now I'm going to pause and
let you try and measure that.
And then we'll show you the answer on
the screen for this particular strip.
Step four. Now we're going
to measure the QRS duration.
Now we have it marked for you here.
You want to measure it when that Q wave
dips down below that isoelectric line
up to the R and to the S.
What we're looking for is a normal value, so
that's less than 0.12 seconds
or 3 small squares.
Remember, each tiny square is worth .04
seconds, so 3 x .04 would be .12.
And that's the number you're looking
for, a QRS that is less than .12.
Step five is to look at the ST segment.
You want to make sure there's
no depression or elevation.
Remember, we're comparing
that to the isoelectric line.
Step six, examine the T wave.
Make sure that it's rounded
and not peaked or tall.
Now the seventh step we talked about,
we're looking for QT elongation.
Remember, greater than 50,
we're in really big trouble.
Normal is less than 0.46 in women,
and less than 0.45 seconds in men.
So you've done it all seven steps.
You've walked through this strip to analyze what
it looks like to have a normal sinus rhythm strip.
Now QT interval extends from
the beginning of the QRS complex
through the ST segment and
to the end of the T wave.
And within the cardiac cycle,
it represents the entire process
of ventricular depolarization and repolarization.
So let's review why this is normal sinus rhythm.
The heart rate is between 60 and 100.
The rhythm is regular.
There's a P wave before every
QRS and they look the same.
The PR interval falls between 0.12 to .20,
and the QRS is less than 0.12 seconds.