 ## ECG Rate Interpretation

If a different paper speed is used, calculations will have to be modified appropriately.

##### A. The standard paper speed is 25mm/sec:
• 1mm (small square) = 0.04 sec (40ms)
• 5mm (large square) = 0.2 sec (200ms)

#### B. Paper speed: 50mm/sec

• 1mm (small square) = 0.02 sec (20ms)
• 5mm (large square) = 0.1 sec (100ms)
Show ECG measurements at 50 mm/sec

#### Why use 50 mm/second?

Doubling the standard rate can reveal subtle ECG findings hidden at the slower rates

#### C. Paper speed: 10mm/sec

• 1mm (small square) = 0.1 sec (100ms)
• 5mm (large square) = 0.5 sec (500ms)

### Estimate the rate

##### At a paper speed of 25 mm/second
• 1 SMALL square = 0.04 seconds
• 5 SMALL squares = 1 LARGE square = 0.2 seconds
• 5 LARGE squares = 1 second
• ECG rhythm strip:
• = 250 SMALL squares = 50 LARGE squares = 10 seconds
• To calculate beats per minute (bpm):
• 1500 SMALL squares = 300 LARGE squares = 1 minute
##### There are multiple methods to estimate the rate:

We can calculate the beats per minute (bpm) by dividing 1500 by the number of SMALL squares between two R waves (R-R interval = one beat)

We can calculate the beats per minute (bpm) by dividing 300 by the number of LARGE squares between two R waves (R-R interval = one beat)

REGULAR rhythms

• Rate = 300 / number of LARGE squares between consecutive R waves.

Very FAST rhythms:

• Rate = 1500 / number of SMALL squares between consecutive R waves.

SLOW or IRREGULAR rhythms:

• Rate = Number of R waves X 6
• The number of complexes (count R waves) on the rhythm strip gives the average rate over a ten-second period. This is multiplied by 6 (10 seconds x 6 = 1 minute) to give the average Beats per minute (bpm)

Example of 1500 (small squares) versus 300 (large square) method

Now adding the R wave (10 second rhythm strip)

Note:

• Calculate atrial and ventricular rates separately if they are different (e.g. complete heart block)
• The machine reading can also be used and is usually correct — however, it may occasionally be inaccurate in the presence of abnormal QRS/T-wave morphology, e.g. may count peaked T waves as QRS complexes or miss QRS complexes with reduced amplitude.

• Normal: 60–100 beats/min
• Tachycardia: >100 beats/min

Normal Heart Rates in Children

• Newborn: 110 – 150 bpm
• 2 years: 85 – 125 bpm
• 4 years: 75 – 115 bpm
• 6 years+: 60 – 100 bpm

#### References 