If the AV Node was acting as the pacemaker what change would you see on EKG?

Answer 1

If the SA node and all other atrial pacemakers fail, or there is an electrical disconnect between the atria and the ventricles (AV block) and the AV node is acting as the primary pacemaker for the heart, you will notice several things.

The first thing you would notice is the rate. The normal rate for the Sinoatrial node is 80-100 bpm. For all the other atrial pacemakers, it is very close to that, but slightly slower. The intrinsic rate of depolarization for the AV node is slower, about 40-60 bpm. You would notice a heart rate in the 40-60 bpm range on the EKG or monitor.

The next thing you would notice is the lack of a P wave before every QRS, or if you did notice a P wave, you may notice it just before, during, or after the QRS, and it would look abnormal. This is because when the AV node depolarizes, the electrical signal sometimes transmits in a retrograde fashion up into the atria, resulting in an abnormal P wave that is typically inverted and in an abnormal location when compared to normal.

The third thing you would notice, if the signal is coming from the bundle of HIS or septal purkinje system is the presence of a bundle branch block, which is a widening of the QRS and what is typically referred to as a "bunny ear," or RsR' pattern. However, if the signal is coming from the AV node itself, the QRS will appear normal.