How To Read An ECG

The ECG paper is mostly standardised

• Each large square on the paper represents 0.2 seconds
• Each small square represents 0.04 seconds
• 5 large squares therefore = 1 second
• 300 large squares = 1 minute
• To calculate heart rate – count large squares within an R-R interval & divide 300 by this number

P-waves

• P-waves represent atrial depolarisation
• There should be a P-wave preceding each QRS complex

QRS complex

• The QRS-complex represents depolarisation of the ventricles
• It is seen as 3 closely related waves on the ECG (Q,R & S wave);
• The first downward deflection is the Q-wave
• Any upward deflection is an R-wave
• Downward deflections after an R-wave is called an S-wave
• It should be between 0.06-0.10 seconds

T-wave

• The T-wave represents ventricular re-polarisation
• It is seen as a small wave after the QRS complex

Source: facmedicine