Hello everyone,its me again,hope you are all doing well and i am too and without any delay we have to enter into learning process.
Today i came up with one important and interesting topic that is Calculating heart rate from ECG strip
Firstly, we should know what's the normal heart rate? NCBI said that its range from 60 to 100 beats per minute.
as per NCBI
- Heart rate less than 60 is called bradycardia
- Heart rate more than 100 is called tachycardia
To know how to calculate it, first of all we need to understand the ECG strip.
Lets see,
here you can see the ECG paper strip has many Square boxes on it and the waves you see on it are the representation of the electrical activity of heart(for every contraction
& relaxation).
Image source
It has "P" wave "QRS" complex and T wave.the "QRS" complex has "Q"wave,"R"wave and "S" wave.the "R" wave is the tallest one(sharp/spike).the distance between 2 "P"waves or 2 "R"waves is one single beat.
Now look at the ECG paper strip.the ECG paper strip moves at a speed of 25 mm/second .this speed is constant and the recordings of heart contraction on the ECG paper are taken when it moves.
The ECG paper has many number of small square boxes and you can notice it that i marked them.we need to know the dimensions of these small square boxes.each small square box is 1mm length in X-axis and 1mm in Y-axis.you can see i labelled it.
1 small square box = 1 mm
we know that ECG paper moves at a speed of 25 mm/sec.so, for 1 minute(60 seconds) the ECG paper paper moves 25×60=1500mm distance.now we have to know how many small boxes that it has covered in this 1500mm distance.
Each small square box length on X-axis is 1mm(1 small square box=1mm ).
so in 1500mm length,there are 1500 small boxes(1500mm=1500 small square boxes)
After understanding all these things,now we need to understand a bit further.we learnt that a single beat represents the distance between two successive "P" waves or two successive "R" waves.we can take any of the above two.for easy counting we take the interval between two "R" waves(as R waves are seen clearly).it represents 1 single beat.
1 beat = distance between 2 successive "R"waves
now calculate how many small square boxes are there between 2 successive "R" waves?.
Lets see the below ECG strip for this -
I labelled the small square boxes we have to take a single row in X-axis like in the image between 2 successive "R" waves
Image source
You can see there are 24 small square boxes between 2 successive "R" waves(single beat). it means for 24 small square boxes we got one single beat.Therefore,for 1500 small square boxes(which represents 1 minute/60 sec as we discussed above) how many beats are occuring? Lets now calculate -
24 small square boxes = 1 beat
1500 small square boxes(1min) = ?? beats
1500÷24 =62 beats/minute
So we get 62 beats per minute.that is the heart rate.
now we got the formula for calculating heart rate. the formula is
Heart rate= [1500÷number of small square boxes between two successive "R" waves]
References -
1)https://www.uptodate.com/contents/ecg-tutorial-basic-principles-of-ecg-analysis
2) Harrison's Principles of Internal Medicine 20th edition page number-1676
3) Ganong' review of Medical Physiology,26th edition page number-514
4) Rapid Interpretation of EKG's:Dr Dubin's Classic Simplified methodology for Understanding EKG's 6th edition page number - 27
In summary
Take a ECG paper strip that has recordings.
Find "R" waves
count number of small square boxes in a single row in between two successive "R" waves
Divide 1500 by the number of small square boxes that you got and you get the heart rate.
As it is important to know basics,i would like to give you some exercise for this.
i am sharing three ECG strips below and you please calculate heart rate of each ECG strip and put your answers in comment section.
1
2
3
Thanks for reading,
With regards
