Question

how the rate of heart beat determined from ECG

Answer 1

to go by RR or PP interval. If it is 1 big box (0.2 secs) then the rate is 60/0.2 = 300 bpm. The rest of the sequence would be as follows. Count the number of RR intervals between two Tick marks (6 seconds) in the rhythm strip and multiply by 10 to get the bpm

Answer 2

When the cardiac rhythm is regular, the heart rate can be determined by the interval between two successive QRS complexes. On standard paper with the most common tracing settings, the heart rate is calculated by dividing the number of large boxes (5 mm or 0.2 seconds) between two successive QRS complexes into 300. For example, if the interval between two QRS complexes is two large boxes, then the rate is 150 beats per minute (bpm) (300 ÷ 2 = 150 bpm).