###### Calculation of heart rate from ECG

In my last post I have enumerated the points for studying an ECG.

The first step is to check the calibration and paper speed. Then comes the calculation of heart rate. There are various methods of calculating the heart rate from ECG. We will discuss about the most commonly used and authentic methods of calculation.

ALL THESE METHODS ARE APPLICABLE FOR PAPER SPEED OF 25MM/SEC.

No.1 and 2 are applicable for a regular heart rhythm. No.3 is applicable for irregular heart rhythm

No.1: Calculate the number of large boxes

Count the number of large boxes between two consecutive R-R waves. 300 divided by the number of large boxes between two consecutive R-R waves is the heart rate. In figure 1 there are 3 large boxes between two consecutive R-R waves, so the heart rate is 300/3 =100/minute.

No.2: Calculate the number of small boxes

Count the number of small boxes between two consecutive R-R waves. 1500 divided by the number of small boxes between two consecutive R-R waves is the heart rate. In figure 1 there are 16 small boxes between two consecutive R-R waves, so the heart rate is 1500/16 = 94/min. This method is more accurate than the previous method.

No.3: Calculate the total number of R-waves in the rhythm strip

This method is applicable when the heart rate is irregular e.g. in patients with atrial fibrillation, frequent VPCs etc. At a paper speed of 25 mm/sec the duration of a 12-lead ECG is 10 seconds. So count the total number of R-waves in the rhythm strip (the long lead II at the bottom of the ECG ) and multiply it by 6 to get the heart rate. In the example shown below there are frequent VPCs.

The total number of R-waves is 12. So the heart rate is 12×6 = 72/min

I suggest you practice all the methods in the beginning so that after sometime you will be well habituated to use a method as needed.

Next week we will discuss about analyzing rhythm from ECG.