Email Address
Password
Remember me on this computer
Register New Account
Forgot your password?
Email Address
Please fill the email address you used for registration. An email with password reminder will be sent to you.
Back to sign in screen
Don't have an account?
An email has been sent to you with your password. please check your email inbox.
Back to sign in screen
Don't have an account?
Module title = Tutorial: Analyze the Waveforms
Lesson title = PR Interval
This is lesson 9 of 11 in this module
In this lesson, we will cover how to measure the PR interval. Remember that the PR interval starts at the
start
of the P wave and ends at the
start
of the QRS:
There are
2 questions
you must ask when you measure the PR interval:
how long is it?
is it changing?
One little square on the ECG is 0.04 seconds. The
normal PR interval
is
3-5 little squares
= 0.12-0.20 seconds
The PR interval options are:
normal
too short
too long, constant
too long, changing
not applicable (in other words, does not exist)
Not applicable??
if you have no P wave, you can have no PR interval
if you have no QRS, you can have no PR interval
if the P wave is ridiculously far away (or even after the QRS), then you have no PR interval
Please note:
the QRS complex does not always contain a Q, an R, and an S wave. Sometimes there is only a single deflection (which, if upward would be called an R and if downward would be called a Q). Regardless of the configuration of waveforms within the QRS complex, we still measure to the
start of ventricular depolarization
, even if it starts with an R wave instead of starting with a Q wave.
What it means when the PR interval is abnormal:
PR interval is
long
:
there is slow conduction through the AV node (called first degree heart block)
PR interval is
short
:
origin is the AV node (called "junctional" rhythm)
accessory pathway is present
In the
Rhythms Diagnostic Criteria tutorial
, we will cover in more detail about
first degree heart block
and
junctional rhythm
and we have super wicked animated videos to try to help explain all this stuff. Accessory pathways are rare and will be described in a more advanced tutorial later.
Examples:
for each ECG, indicate the length of the PR interval and if it is changing:
PR interval is
6 little squares
= 0.24 sec = long, and is constant
What about this one?
The PR interval is
changing
. It starts normal then is long. Then you can see a QRS is missing. Zoomed in, we are showing blue lines to indicate the 2 different PR intervals:
Here is a difficult one:
The PR interval in this example is different every time. Therefore, we cannot describe it. The PR interval in this example is "not applicable".
Here is another example where the PR interval is not applicable:
Practice PR interval analysis now.
Lesson 9 of 11
That was the last lesson!
