Electrocardiograms Quiz

See The Conduction System. The atrioventricular (AV) node (E) slows the electrical impulse between the atria and ventricles. It lies in the lower part of the right atrium near the wall separating the atria. Slow conduction through the node gives atrial contraction time to contribute to ventricular filling before ventricular contraction begins. After this delay, the impulse enters the faster specialised pathways that distribute it through the ventricles. A useful way to remember the sequence is: the SA node starts the beat, the AV node delays it, and the His-Purkinje network distributes it.

The sinoatrial node (C) is the usual pacemaker and begins atrial activation. The bundle of His (B) carries the impulse onwards from the AV node into the ventricular conduction system. Purkinje fibres (A) spread the signal rapidly through the ventricular muscle, helping the ventricles contract in a coordinated way. The right bundle branch (D) is the route to the right ventricular conduction network, rather than the site of the normal AV delay.