ECG Rate Interpretation
Understanding paper speeds
- Paper output speed is the rate at which the ECG machine produces a trace
- Standard output is 25mm per second
- If a different paper speed is used, standard rate calculations will have to be modified appropriately (see other examples below)
The standard paper speed is 25mm/sec:
- 1mm (small square) = 0.04 sec (40ms)
- 5mm (large square) = 0.2 sec (200ms)
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.
Interpretation (adults)
- Normal: 60–100 beats/min
- Tachycardia: >100 beats/min
- Bradycardia: <60 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
Other paper speeds: 50mm/sec
Doubling the standard rate will cause the ECG to appear drawn out or wider complex than 25mm/sec paper speeds
- 1mm (small square) = 0.02 sec (20ms)
- 5mm (large square) = 0.1 sec (100ms)
Why use 50 mm/second?
Doubling the standard rate can reveal subtle ECG findings hidden at the slower rates, in particular atrial flutter waves in a 2:1 block:
C. Paper speed: 10mm/sec
- 1mm (small square) = 0.1 sec (100ms)
- 5mm (large square) = 0.5 sec (500ms)
References
- Accardi A, Miller R, Holmes J. Enhanced diagnosis of narrow complex tachycardias with increased electrocardiograph speed. J Emerg Med. 2002;22(2):123-126
- 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.
- Lin M. Trick of the Trade: Speed up ECG paper rate to differentiate tachycardias
Advanced Reading
Online
- Wiesbauer F, Kühn P. ECG Yellow Belt online course: Become an ECG expert. Medmastery
- Wiesbauer F, Kühn P. ECG Blue Belt online course: Learn to diagnose any rhythm problem. Medmastery
- Rawshani A. Clinical ECG Interpretation ECG Waves
- Smith SW. Dr Smith’s ECG blog.
Textbooks
- Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
- Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
- Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
- Hampton J. The ECG Made Practical 7e, 2019
- Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography 1e, 2009
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
- Mattu A, Brady W. ECG’s for the Emergency Physician Part I 1e, 2003 and Part II
- Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004
LITFL Further Reading
- ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
- ECG A to Z by diagnosis – ECG interpretation in clinical context
- ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
- 100 ECG Quiz – Self-assessment tool for examination practice
- ECG Reference SITES and BOOKS – the best of the rest
ECG LIBRARY
Electrocardiogram
MBBS (UWA) CCPU Emergency Medicine Advanced Trainee based in Melbourne, Australia. Co-author of the LITFL ECG Library. Likes Ultrasound, Echo, ECGs, and anything and everything with caffeine. Part of the 2021 ANZCEN Clinician Educator Incubator Programme | @rob_buttner | ECG Library |
It was very effective. Thank you Doctor. Best regards.
it is very informative and easily understandable.
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Thank you for sharing your knowledge perfectly. This ECG Library is brilliant. That’s what I was looking for! I really enjoy the podcasts too, they are definitely useful. Yes, it is about Life. Congratulations for You and your Colleagues. I share this page with my colleagues and medical students. Greetings from Hungary 😉 Katalin
Ma il genere cosa si usa il 25mm o il 50mm?