Question

What happens in terms of atrium and ventricular contraction when the AV node is the pacemaker? What does this look like on an ECG?

Answer 1

When AV node act as a pacemaker, atrium and ventricle contract together at the same time. In contrast when the SA node work as the pacemaker, first the impulse will be passed to the atrium and cause atrial contraction. Then the impulse is passed to the AV node and cause ventricular contraction. This delay in contraction of ventricle helps in ventricular filling of blood by atrial contraction. This is the normal process and SA node is our normal pacemaker. When AV node take over this function, it causes the atrium and ventricle to contract together at the same time. This contraction disrupt the normal heart mechanism. In this contraction due to AV node pacemaker, P wave (represent atrial contraction) will be absent in the ECG reading because P wave will be masked or hidden in QRS complex (represent ventricular contraction) as the atrium and ventricle are contracted together.