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Dx Wisely
ECG
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ECG
Level 1
Tutorial: Analyze the Waveforms
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Tutorial: Analyze the Waveforms
This module will teach the basic waveforms on ECG and a stepwise approach of how to analyze them. Practice each step and get feedback on your performance.
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Develop your skills by completing our
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Tutorial: Analyze the Waveforms
QRS Width
Lessons
42
Times Practiced
1284
Cases Completed
1h 24m
Total Time spent
1m 24s
Average Time
Progress
Accuracy
Efficiency
Accuracy
Efficiency
1
Anatomy
Anatomy
2
Waveform Identification
Waveform Identification
3
Waveform Identification #2
Waveform Identification #2
4
Determine the heart rate
Determine the heart rate
5
Do you have Rhythm?
Do you have Rhythm?
6
P waves! Where are you?
P waves! Where are you?
7
How many P waves?
How many P waves?
8
P wave Size and Shape
P wave Size and Shape
9
PR Interval
PR Interval
10
P conducted to QRS?
P conducted to QRS?
11
QRS Width
QRS Width
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Practice
Finish Module
Previous
Practice
QRS Width
The criterion to
differentiate wide vs. normal QRS is 120 ms
. which is
3 little squares
:
less than or equal to 120 ms is narrow, which is
normal
greater than 120 ms is wide
The width of any waveform on the ECG is dictated by
conduction speed
through the heart:
an electrical event that is
slow
will be spread out over more time and therefore will be
wide
an electrical event that is
fast
will be completed quickly and therefore will be
narrow
Remember that normal conduction through the ventricles starts with the Purkinje fibers, which are fast conducting fibers and when these fibers are used, the electrical signal is very rapidly spread through both ventricles and the QRS will be narrow.
Super important causes of slow conduction (wide QRS):
conduction from ventricular myocyte to myocyte is
much slower
compared to the purkinje fibers. This happens when an electrical signal
STARTS in the ventricle muscle
.
diseased conducting fibers, typically called
conduction delay
,
aberrancy
, or
bundle branch block.
For more details on bundle branch block and conduction delay, see the
Bundle Branch Block tutorial
. In brief, with
bundle branch block
one of the bundle branches is not conducting. Therefore, the electrical signal moves quickly down from the AV node through one bundle branch, but to get to the
other side of the heart
, the signal must be conducted from myocyte to myocyte, which is slow conduction. This requires extra time and causes the QRS to be wide.
Here is an example of narrow QRS:
The signal in this ECG travels through the fast purkinje fibers and rapidly depolarizes both ventricles. This occurs very quickly, so the QRS is narrow.
When you
apply calipers
, you can see that the QRS duration is less than 120 ms (3 little squares):
Here is an example of a wide QRS:
The calipers show the QRS duration to be 155 ms:
How about this ugly one?
That is very wide. It is virtually impossible to identify the start and finish of the QRS.
Try practicing the QRS width.
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Practice
Finish Module
Previous
Practice