Heart Education Awareness Resource and Training through eLearning (HEARTe)


Electrical activity of the heart

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.

Page last reviewed: 20 May 2020