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.

**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

#### References

- Lin M. Trick of the Trade: Speed up ECG paper rate to differentiate tachycardias
- Larkin J. ECG of the Week – 20th August 2012
- Accardi A, Miller R, Holmes J. Enhanced diagnosis of narrow complex tachycardias with increased electrocardiograph speed.
*J Emerg Med*. 2002;22(2):123-126. [PMID 11858914] - 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. [PMC1726576]

#### 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

#### Advanced Reading

- Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
- Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
- Wagner GS. Marriott’s Practical Electrocardiography 12e
- Chan TC. ECG in Emergency Medicine and Acute Care
- Rawshani A. Clinical ECG Interpretation
- Mattu A. ECG’s for the Emergency Physician
- Hampton JR. The ECG In Practice, 6e

## ECG LIBRARY

Electrocardiogram