• RR interval: Is the RR-interval equal? Variations must be <3mm (3 small box) between QRS complex
  • PP interval: Is the PP interval equal?
  • Identify overall rhythm (normal, irregular (bradycardic or tachycardic)
  • Normal Sinus Rhythm (NSR) – 60 to 100bpm
  • Bradycardic (Slow) – Lower than 60bpm
  • Tachycardic (Fast) with narrow QRS (< 0.12s QRS duration); faster than 100bpm
  • Tachycardic (Fast) with wide QRS (> 0.12s QRS duration); faster than 100bpm
  • Identify the heart rate – noting the rate (bpm); If the rhythm is irregular, then compares the ECG’s heart rate with the manual rate identification method.
P Wave & PR Interval Check
  • One (1) P-wave before every QRS complex; each P-wave is identical in size, shape, & position
  • Positive in Lead II mostly (other leads are Leads III, & aVF but variate)
  • Small & rounded
  • Amplitude 0.5 – 2.5mm
  • Duration < 0.10s
PR Interval:
  • 0.12 – 0.20s (3 to 5 small box)
QRS Complex Check
  • QRS after each P-wave
  • QRS duration 0.08 – 0.10s (2 to 2.5 small box)
  • Normal R-wave progression in V1 to V6?
  • Cardiac axis (Normal or deviated
    • LAD: Left Axis Deviation
    • RAD: Right Axis Deviation
    • EAD: Extreme Axis Deviation
  • Search for abnormal QRS complex
  • Q-waves > 0.03s &/or QRS amplitude is > 25% of R-wave amplitude in same leads AND;
  • Appear in 2 contiguous leads
ST Segment Check
  • Flat & isoelectric unless upsloping into a T-wave
  • ST deviation measured from J-point must be < 1mm maximum (< 0.5mm is ideal)
T-Wave Check
  • Above isoelectric line
  • Each T-wave identical in size & shape (rounded & slight asymmetric) – Repeat every QRS Complex
  • Duration 0.10 – 0.25s
  • Normal T-wave progression as per R-wave progression
  • Amplitude < 5mm and highest in Lead II, & V2-V3
  • QT duration is 0.35 – 0.43s


College of Pre-Hospital Care. (2015). 12-Lead ECG Analysis: Self-Directed Learning Package. Version 3. St John Ambulance Ltd.  

Curtis, K., & Ramsden, C. (2016). Emergency and trauma care for Nurses and Paramedics (2nd ed.). Elsevier Australia.

DeLaune, S. C., Ladner, P. K., McTier, L., Tollefson, J., & Lawrence, J. (2016). Australian and New Zealand fundamentals of nursing (1st ed.). Cengage Learning Australia Pty Limited.

ECG & ECHO Learning. (2020). Clinical ECG Interpretation. https://ecgwaves.com/topic/ecg-normal-p-wave-qrs-complex-st-segment-t-wave-j-point/

Life in the Fast Lane. (2020). ECG Library. https://litfl.com/ecg-library/

St John WA Ltd. (2017). Electrocardiography (ECG). Clinical Resources. https://clinical.stjohnwa.com.au/clinical-skills/assessment/vital-signs/electrocardiography-(ecg)

WikiEM. 2020. The Global Emergency Medicine Wiki. https://www.wikem.org

Page contributors:

60825Thanh Bui, AP60825
Event Medic, Emergency Medical Technician &
Volunteer Development Officer



Andrew Moffat, AP16790
Volunteer Training Manager & Volunteer Development Officer

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