<P> Under normal conditions, electrical activity is spontaneously generated by the SA node, the cardiac pacemaker . This electrical impulse is propagated throughout the right atrium, and through Bachmann's bundle to the left atrium, stimulating the myocardium of the atria to contract . The conduction of the electrical impulses throughout the atria is seen on the ECG as the P wave . </P> <P> As the electrical activity is spreading throughout the atria, it travels via specialized pathways, known as internodal tracts, from the SA node to the AV node . </P> <P> The AV node functions as a critical delay in the conduction system . Without this delay, the atria and ventricles would contract at the same time, and blood wouldn't flow effectively from the atria to the ventricles . The delay in the AV node forms much of the PR segment on the ECG, and part of atrial repolarization can be represented by PR segment . </P> <P> The distal portion of the AV node is known as the bundle of His . The bundle of His splits into two branches in the interventricular septum: the left bundle branch and the right bundle branch . The left bundle branch activates the left ventricle, while the right bundle branch activates the right ventricle . </P>

Where is the av nodal delay represented in the ecg