intervals and waveforms

P wave

atrial depolarisation, begins when SA node fires

QRS complex

ventricular depolarisation, 0.04 to 0.10 secs

J point

where ventricular depolarisation stops, and ventricular repolarisation starts

T wave

ventricular repolarisation

U wave

repolarisation of the Bundle of His and Purkinje fibers

PR interval

beginning of atrial depolarisation to beginning of ventricular depolarisation

P-P interval

time between atrial depolarisation cycles

R-R interval

time between ventricular depolarisation cycles

QT interval

one complete ventricular cycle

PR segment

end of atrial contraction and beginning ventricular contraction

ST segment

early phase of ventricular repolarisation