Teaching Medicine - Tutorial: Analyze the Waveforms

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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Tutorial: Analyze the Waveforms QRS Width

Lessons

Times Practiced

1284

Cases Completed

1h 24m

Total Time spent

1m 24s

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	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

Practice

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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):
Using calipers

Here is an example of a wide QRS:

The calipers show the QRS duration to be 155 ms:
QRS duration is 155 msec

How about this ugly one?
Very wide QRS

That is very wide. It is virtually impossible to identify the start and finish of the QRS.

Try practicing the QRS width.