Calculating Heart Rate on an ECG: Explained

Calculating rate

There are three main methods of calculating Heart rate on an ECG. There is no specific best method, and preference varies between clinicians. However, certain methods may be better suited for rhythms such bradyarrhythmia’s or tachyarrhythmias.

ECG Paper Calibration:

1. Standard ECG paper: 25 mm/sec.
2. Each small box: 1 mm = 0.04 seconds.
3. Each large box: 5 mm = 0.2 seconds.

1) Large square method

• Recall above those 300 large squares is equal to 1 minute at a paper speed of 25mm/sec
• We can thus calculate bpm by dividing 300 by the number of LARGE squares between each R-R interval (space between two consecutive R waves = one beat)
• For example, two large squares between each R-R interval implies a rate of 150 bpm, three implies a rate of 100 bpm and so forth:

• Useful as quick calculation for regular rhythms at regular rate

2) Small square method

• Similar to above, except 1500 is divided by the number of SMALL squares between consecutive R waves
• For example, 10 small squares between R-R interval implies a rate of 150 bpm, 15 implies a rate of 100 bpm, and so forth:

Small square method: Divide 1500 by number of small squares between R-R interval.

• Useful for very fast regular rhythms, as likely to provide more accurate rate than large square method

3) R wave method

• Rate = Number of R waves (rhythm strip) 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)
• Useful for slow and/or irregular rhythms

Comparison of three methods: The R wave method is often easiest as a quick calculation

How to Count Atrial and Ventricular Rate using the 6 Second Rule

Atrial Rate

1. Identify the p-waves
2. Beginning at the first p-wave start counting 30 large squares.
3. Then count how many p-waves are between the 30 large squares.
4. Take that number and multiple it by 10 and this is your heart rate.

Ventricular Rate

1. Identify the r-waves
2. Beginning at the first r-wave start counting 30 large squares.
3. Then count how many r-waves are between the 30 large squares.
4. Take that number and multiple it by 10 and this is your heart rate.

Important Considerations:

1. Ensure accurate measurement of RR interval.
2. Use a calibrated ECG paper.
3. Consider arrhythmias and irregular heart rhythms.
4. Verify heart rate with clinical assessment.

ECG Paper Calibration:

Interpretation (adults)

• Normal: 50 – 100 bpm
• Tachycardia: > 100 bpm
• Bradycardia: < 50 bpm

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

1. Accardi A, Miller R, Holmes J. Enhanced diagnosis of narrow complex tachycardias with increased electrocardiograph speed. J Emerg Med. 2002;22(2):123-126
2. Gaspar J, Body R. Best evidence topic report. Differential diagnosis of narrow complex tachycardias by increasing electrocardiograph speed. Emerg Med J. 2005;22(10):730-732.
3. Lin M. Trick of the Trade: Accardi A, Miller R, Holmes J. Enhanced diagnosis of narrow complex tachycardias with increased electrocardiograph speed. J Emerg Med. 2002;22(2):123-126
4. Mike Cadogan and Robert Buttner, Life in the Fastlane, ECG Rate Interpretation Retrieved from https://litfl.com/ecg-rate-interpretation/

Stories are the threads that bind us; through them, we understand each other, grow, and heal.

JOHN NOORD

Connect with “Nurses Lab Editorial Team”

I hope you found this information helpful. Do you have any questions or comments? Kindly write in comments section. Subscribe the Blog with your email so you can stay updated on upcoming events and the latest articles.