Electrical Conduction and ECG

Nodes of the heart

Sinoatrial SA node (pacemaker of heart, autorhythmic), atrioventricular AV node

Describe pathway of conduction through heart

Depolarisation occurs at SA node and sends action potential to left and right atriums, action potential spreads to AV node, action potential spreads down AV bundle or bundle of His, spreads down bundle branches to supply inner ventricular walls and travels superiorly via Purkinje fibres to supply outer ventricular walls

P wave on ECG

Depolarisation of atria

QRS wave complex on ECG

Depolarisation of ventricles, also includes repolarisation of atria but hidden

T wave on ECG

Repolarisation of ventricles

Depolarisation of SA node

Atrial depolarisation = atrial contraction = atrial systole = P wave

Depolarisation of AV node to depolarisation of Purkinje fibres

Ventricular depolarisation = ventricular contraction = ventricular systole = QRS wave

Also includes atrial repolarisation = atrial relaxation = atrial diastole

Repolarisation of ventricles

Ventricular relaxation = ventricular diastole = T wave

Lub vs Dub sound

Lub = closing of av valves closing, dub = closing of semilunar valves