Question

Determine rates and measure intervals and complexes related to EKGs.

Answer 1

The rate of paper (i.e. of recording of the EKG) is 25 mV/s which results in:

1 mm = 0.04 sec (or each individual block)
5 mm = 0.2 sec (or between 2 dark vertical lines)
Distance between Tick marks = 3 seconds (in the rhythm strip)

The voltage recorded from the leads is also standardized on the paper where 1 mm = 1 mV (or between each individual block vertically) This results in:

1 mm = 0.1 mV
5 mm = 0.5 mV (or between 2 dark horizontal lines)
10 mm = 1.0 mV

Heart rate calculation:

Normal range at rest is between 60-100 beats per minute (bpm).

The basic way to calculate the rate is quite simple. You take the duration between two identical points of consecutive EKG waveforms such as the R-R duration. Take this duration and divide it into 60. The resulting equation would be:

Rate = 60/(R-R interval)

A quicker way to obtain an approximate rate is

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.

1 big box = 300 beats/min (duration = 0.2 sec)
2 big boxes = 150 beats/min (duration = 0.4 sec)
3 big boxes = 100 beats/min (duration = 0.6 sec)
4 big boxes = 75 beats/min (duration = 0.8 sec)
5 big boxes = 60 beats/min (duration = 1.0 sec)

Count the number of RR intervals between two Tick marks (6 seconds) in the rhythm strip and multiply by 10 to get the bpm. This method is more effective when the rhythm is irregular.