If There is a Complete Block Between the SA Node

Question

If there is a complete block between the SA node and the AV node, how would the ECG be affected?
A) The P-R interval will be shorter.
B) The QRS duration will be longer.
C) There will be much bigger P waves.
D) The ventricles will stop beating.
E) The rate of P waves will be faster than the rate of QRS complexes.

Accepted Answer

In the case of a complete block between the SA node and the AV node, the atria and ventricles beat independently of each other. The SA node continues to pace the atria, resulting in P waves at a normal rate, but the ventricles are paced by a lower pacemaker site (e.g., the AV node or Purkinje fibers) at a slower rate, leading to a slower rate of QRS complexes. This results in the rate of P waves being faster than the rate of QRS complexes.