b'D R S A B C DDefibrillationElectrophysiology of the HeartThe heart has specialised cells that generate electrical impulses in the muscle fibre cells in the heart. These impulses transmit through the heart by conductive tissue and give the heart the ability to beat on its own.Heart rhythm is initiated by a group of pacemaker cells in the atrial wall (SA node) that discharge at regular intervals, normally 60 to 100 times per minute. The impulse is conducted along a pathway to another group of pacemaker cells (AV node), discharging at 40 to 60 times per minute. The impulse then travels along an intricate group of pathways (Bundle of His) and through the Purkinje Fibres, discharging in a coordinated manner (20 to 40 times per minute). This electrical activity stimulates mechanical activity in the form of muscle contraction producing a heartbeat. Repeated electrical activity of this type is known as sinus rhythm.Any interruption of the coronary circulation, trauma or disease can disrupt the creation or pathway of these electrical impulses. Rhythm disturbances can result and some of these can be fatal.Right LeftAtrium AtriumLeft VentricleRight VentricleBundle BranchesResuscitation 53'