Rate determination is the first step in the interpretation of any ECG. It is simple in regular rhythms. However, students may find it difficult for irregular rhythms. After reading through this article, you will be confident in calculating the rate of both regular and irregular rhythms.
Before starting, let me ask you which is the best lead to calculate heart rate in ECGs?
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Yes, you’re right! Lead-II is the standard lead for checking rate and rhythms. It is also known as the rhythm strip. In modern machines, this is printed automatically in the lower portion of a 12-lead ECG, but in older machines, you have to pull out a long strip of lead-II manually.
The rhythm strip by convention is 6 seconds long which means 30 large squares on ECG paper. This is important when we will discuss heart rate calculation in irregular rhythms. Now we are good to go!
Method 1
Step – 1: Find the Right R-wave 🙂
In a rhythm strip, try to find an R-wave that falls on the thick line of a large square.
Step – 2: Calculate squares till next R-wave
Calculate the number of large squares between it and the next R-wave. You can also calculate the number of small squares if you want to be more precise in the calculation.
Step – 3: Apply the Equation
You may now calculate the heart rate by simply applying these simple equations. The first one is for the calculated large square and the other one is for the calculated small squares between two consecutive R-waves.
Heart rate = 300 / Number of big squares
Heart rate = 1500 / Number of small squares
Method 2
Step – 1: Remember 300, 150, 100, 75, 60, 50 🙂
Try memorizing these numbers in same order! 300, 150, 100, 75, 60, 50. These are the numbers given to the big lines of large squares in descending order. The nearest big line that you are on will get 300, the next 150, the very next 100 and so on. But what line you shall be on? Let’s find in step 2.
Step – 2: Find the Right R-wave 🙂
As in the previous method, try to find an R-wave that falls on the thick line of a large square in the rhythm strip. This is the same line you are on we talked about in step-1 & now you are ready to calculate heart rate. Let’s proceed to step-3.
Step – 3: Calculate rate by application of 300, 150, 100 …
Apply the numbers you have just learned. If the next R-wave is falling on the very next big line, then the heart rate is 300 (practically 300/min heart rate is rare). If it is on the 2nd next, then heart rate is 150/min, and so on.
Method 3
Step – 1: Calculate the number of R-waves
Take the rhythm strip & calculate the number of R-waves present in 6 seconds (i.e., 5 large squares)
Step-2: Multiply by 10 😉 simple!
Now multiply the number of R-waves, you gained in 6 seconds, by 10 to get the heart rate. For example, if the number of R-waves in the 6-second strip was 10. 10 x 10 = 100/minutes
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