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Module title = Tutorial: Analyze the Waveforms

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Lesson title = Determine the heart rate

This is lesson 4 of 11 in this module

In this lesson, we will learn how to determine the heart rate.

**(Not so interesting) Math Facts:**ECG paper is measured in mm. A **little square** is 1 mm wide (and tall)

A **big square** is 5 little squares = 5 mm

ECG's are recorded at 25 mm/sec, which means:

1 sec = 25 mm = 5 big squares and

5 x 60 = 300 big squares = 1 minute

Now that was exciting. However, it is the logic behind the method below:

If we had

**one heartbeat with every big square**, then there would be 300 beats per minute (bpm).

If we had one heartbeat every 2 big squares, then the heart rate would be 150 bpm.

If we had one heartbeat every 3 big squares, then the heartrate would be 100 bpm.

Starting to see a pattern?

Simply put,

**Heart rate = 300 / (# of big squares between 2 QRS's)**Sometimes, the rhythm of the ECG is not regular (there will be faster and slower sections). If that is the case, then do your best to take an AVERAGE value for the heart rate. In truth, sometimes the heart rate is variable and changing from minute to minute and there is no single correct heart rate value.

The spacing here is 3 big squares, so 300/3 = 100 bpm

The spacing here is about 1.2 big squares, so the rate is 300/1.2 = 250 bpm (crazy fast!)

The spacing here is about 11 squares, so the rate is 300/11 = 27 bpm

A slightly different way of doing the math is to use small squares instead of big squares. There are 5 small squares in a big square, so the equation becomes (300 x 5) / (small squares) = 1500 / (small squares).

One challenge you will encounter is how to calculate the rate when the rate seems to be changing. For example, if the rhythm is not regular, the rate will apear to be always changing. There are 2 ways to deal with this. First, you can measure a few different QRS complexes and average it out.

The second method is to use a full page 12 lead ECG. A full page 12 lead ECG will have an ECG tracing for 50 big squares. There are 5 big squares in one second, so a full ECG tracing is 10 second long. If you multiply by 6, then you can calculate the rate in one minute.

**Summary:**- rate = 300 / (big squares)
- rate = 1500 / (small squares)
- rate = 6 x (# of QRS) on a full one page ECG

Now go practice your awesome heart rate skills!