ECG Rate Interpretation

The usual paper speed is 25mm/sec:

• 1mm (small square) = 0.04 sec
• 5mm (big square) = 0.2 sec

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

Calculate atrial and ventricular rates separately if they are different (e.g. complete heart block).

There are multiple methods to estimate the rate:

• For regular rhythms:  Rate = 300 / number of large squares in between each consecutive R wave.
• For very fast rhythms:  Rate = 1500 / number of small squares in between each consecutive R wave.
• For slow or irregular rhythms:  Rate = number of complexes on the rhythm strip x 6  (this gives the average rate over a ten-second period).

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. 

Interpretation (adults)

• 60–100 beats/min
  • Normal
• >100 beats/min
  • Tachycardia
• <60 beats/min
  • Bradycardia

Normal Heart Rates in Children

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

Further Reading

• ECG BASICS – Waves, Intervals, Segments and Clinical Interpretation
• ECG CLINICAL CASES – Your favourite ECG’s placed in clinical context with a challenging Q&A approach
• ECG and Cardiology Eponymous Syndromes – Cheats guide to eponymous emancipation
• ECG Reference Sites on the WEB – the best of the rest

Author Credits