How to read a Cardiac Rhythm Strip

Meghan Walter

NURS 609 Week 5

Cardiac rhythm strips although they look daunting are actually quite simple if you read them in a systematic manner. Once you know what's normal, it is easy to figure out what rhythm the patient is in. Let's follow some simple steps and figure them out together!

Download Heart ECG stock vector. Illustration of monitoring, science - 46354916

This is a diagram of the electrocardiograph. The waves and intervals are labeled in this picture.
Image Retrieved from: https://www.dreamstime.com/stock-illustration-heart-ecg-ekg-showing-major-intervals-created-adobe-illustrator-eps-image46354916

Now that we know the basic image we are trying to look at, we will follow a methodical step by step approach to figure out what rhythm we are looking at! On the ECG paper we usually print out a six second recording. Each small box is 0.04 seconds, each large box (5 small boxes) are 0.2 seconds. We need to know this for our interpretations.

1. Is the rhythm regular or irregular?

For this you want to measure the distance between the r-waves (also called the R-R interval). If the distance between consecutive r-waves is the same, the rhythm is regular. If the distance is NOT the same, then we consider this to be irregular.

Let's try it:

Would this rhythm be regular or irregular? (HINT: Check out the distance between the r-waves)

Answer: The distance between the r-waves is the same, this is a regular rhythm.
Image retrieved from: http://www.mauvila.com/ECG/ecg_fundamentals.htm

2. Is there a p-wave for every QRS Complex? Are they normal in appearance?

In a normal sinus rhythm the p-wave precedes the QRS complex. They should be in a 1:1 ratio.

Let's try it:

Does this strip have a p-wave for every QRS?

Answer: Yes. There is a 1:1 ratio between p-waves and QRS complexes. They are normal shape .
Image retrieved from: http://www.mauvila.com/ECG/ecg_fundamentals.htm

3. What is the length of the PR interval? (normal is 0.12-0.2(Diehl, n.d.))

Let's try it:

What is the PR interval?

Answer: The PR interval is approximately 0.16. The start of the p-wave to the r-wave is approximately 4 small boxes on the strip, so 4 x 0.04=0.16 seconds.
Image retrieved from: http://www.mauvila.com/ECG/ecg_fundamentals.htm

4. What is the QRS complex measured at? It should be narrow, wide QRS complexes can be scary! (Normal is 0.04-0.08 (Diehl, n.d.))

Let's try it:
What is the QRS complex measurement?

Answer: The QRS is approximately 1 small box. So, 1 x 0.04=0.4seconds.

Image retrieved from: http://www.mauvila.com/ECG/ecg_fundamentals.htm

5. What is the QT interval? (Normal is 0.36-0.44 (Diehl, n.d.))

Let's try it:
What is the QT interval?

Answer: The QT interval measures from the start of the QRS complex to the end of the T-wave. This is 8 small boxes, so 8 x 0.04 = 0.32. This is a short QT interval.

Image retrieved from: http://www.mauvila.com/ECG/ecg_fundamentals.htm

6. Is is fast or slow? (We are using adults. Normal heart rate is 60-100)

Let's try it:
Is this rhythm fast or slow?
(To do this you can use the "300 Method." Count the number of large boxes between 2 consecutive r-waves and divide 300 by the number of boxes. You could also use the "1500" method where you count the number of small boxes between 2 consecutive r-waves and divide 1500 by the number of boxes (Diehl, n.d.)

Answer: There are 4 large boxes. 300/4=75. So this is approximately 75 bpm. This is a normal rate.

Image retrieved from: http://www.mauvila.com/ECG/ecg_fundamentals.htm

Putting it ALL Together!

We have a normal rate and rhythm. There are p-wave for every QRS. The p-waves are upright and normal shape. The intervals are all within normal limits. Our QT interval is slightly short. This would be a normal sinus rhythm with a shortened QT interval.

TRY SOME ON YOUR OWN: