ABSTRACT
Electrical impulses are required to synchronise the four pumping
chambers. The atria are electrically isolated from the ventricles by a
fibrous atrioventricular separation. The impulse originates in the sino-
atrial (SA) node, travels across the atrial musculature towards the
atrioventricular (AV) node, thence down through the bundle of His to
the ventricles via the right and left bundles and into the Purkinje
system (Figure 1). The SA node has an inherent rate of approximately
70 beats per minute and is under autonomic and chemical hormonal
influence. The inherent rate of the AV node is lower, at 60 beats per
minute, and the ventricles will beat in isolation at approximately 40
or less beats per minute. The electrical impulse, having reached the
ventricular musculature, then travels outwards from the endocardium
to the epicardial surface. The electrical current is produced by a
From the sinoatrial node across the atrial = sinoatrial atrioventricular node; H = bundle of His; RV = right ventricle; LV = left ventricle; RB = right = right atrium; LA = left atrium; SLB = superior left bundle; ILB = inferior left bundle.
