This cat’s heart rate is 200 bpm. When the paper speed is 50 mm/sec, calculate the heart rate by multiplying the number of QRS complexes (rounded to the closest whole number) in 15 cm (or 30 big boxes) by 20. At this speed, 30 boxes is 3 seconds. The cat in this example has 10 complexes in 15 cm, therefore:
20 x 10 = 200 beats per minute (bpm)
Note: At a paper speed of 25 mm/sec, there are 6 seconds per 15 cm/30 boxes. Count the beats in 30 boxes and multiply by 10 for beats per minute.
Can also obtain an instantaneous heart rate in a patient with a regular sinus rhythm by measuring the mm between a single R-R interval. If X is the R-R interval, then heart rate (HR) is:
At 25 mm/sec : 1500/X = HR (bpm)
At 50 mm/sec: 3000/X = HR (bpm)
In this cat, the R-R interval is 15 mm (15 small boxes), therefore:
3000/15 = 200 bpm
Here’s an example:
A resting heart rate in a cat is 180-220 bpm. This is slightly higher than original reported ranges because cats are most often slightly stressed at time of acquisition (i.e., at the vet hospital)
Images courtesy of Jen Mahon, DVM, DACVECC.
