 Paper speed = 25 mm/s
 One large square = 0.2s
 One small square = 0.04s
 Amplitude = 10 mm/mV
Rate Calculation
 Assuming standard paper speed there are several methods to calculate the heart rate.
 Count number of large squares between consecutive R waves and divide into 300.
 Count number of small squares between consecutive R waves and divide into 1500.
 An ECG recoding captures10 seconds of activity, so you can multiple the number of complexes along the rhythm strip by 6 to estimate the rate, a useful method for irregular rhythms.
Normal Ranges
 PR Interval: 0.12  0.2s (35 small squares)
 QRS Duration: < 0.12s (3 small squares)
 QTc usually less than half the RR interval.
 Consider prolonged QTc either > 440ms or > 460ms for males and >470ms for females.
 Considered shortened QTc if < 330ms
Axis
 Normal: 30 degress to 90 degrees
 Left axis deviation: < 30 degrees
 Right axis deviation: > 90 degrees
 Extreme Axis: 180 degrees to 90 degrees
Hex Axial
QRS Nomenclature Examples
The QRS complex represents ventricular depolarisation, however, describing the QRS complex with these three letters is often an oversimplification. A QRS complex may not necessarily contain a Q wave, a R wave, or a S wave, and may contain more than one R wave.
The various deflections of the QRS wave can be notarised as follows:
Capitalisation
of the letter indicates tall or deep waves, with small waves notarised with
small letters.

Q wave –
any initial negative deflection

R wave –
any positive deflection

S wave –
any negative deflection after a R wave

R’ wave –
any positive deflection that follows an S wave

QS complex
– if there is only a single negative deflection
References
 Chan T, Brady W, Harrigan R, Ornato J, Rosen P (2005), ECG in Emergency Medicine and Acute Care, 1^{st} Edition, Elsevier Mosby.
 Hampton J (2003), The ECG in Practice, 4^{th}Edition, Churchill Livingstone.
 Surawicz B, Knilans T (2008), Chou’s Electrocardiography in Clinical Practice, 6^{th} Edition, Saunders Elsevier.
 Morris F, Edhouse J, Brady W, Camm J (2003), ABC of Clinical Electrocardiography, 1^{st} Edition, BMJ Books.