Depolarisation and Repolarisation
The heart cannot pump unless there is electrical stimulus first. As these electrical impulses are initiated from the Sinoatrial node (SA) node and travel in wave form through the heart, a cyclic process of depolarisation and repolarisation occurs. Depolarization is considered to be the active state, and repolarisation is the resting state. During depolarisation and repolarisation, four main electrolytes (sodium, potassium, calcium, and chloride) move across the cardiac cell membrane. These actions are continuous and sequential, and generate the wave form of the ECG. This describes the electrical activity of the heart.
Activation of the atria
P-R interval: the portion of the electrocardiogram between the onset of the P wave (atrial depolarization and the QRS complex (ventricular depolarization)
Activation of the ventricles
QRS interval: the interval from the beginning of the Q wave to the termination of the S wave, representing the time for ventricular depolarization
Recovery wave
T wave: represents the repolarisation (or recovery ) of the ventricles
Ventricular depolarisation and repolarisation electrical activity
Q-T interval: the time from the beginning of the Q wave to the end of the T wave, representing the duration of ventricular electrical activity.
Pulse point
Further reading:
McGraw-Hill Professional: Basic principles of ECG interpretation [PDF]
Page last reviewed: 20 May 2020