Second Degree Type II AV Block

In second degree type II AV nodal block (a.k.a. Mobitz Type II AV block), the AV node becomes completely refractory to conduction on an intermittent basis.

For example, three consecutive P waves may be followed by a QRS complex giving the ECG a normal appearance, then the fourth P wave may suddenly NOT be followed by a QRS complex since it does not conduct through the AV node to the ventricles. The PR interval may be normal or prolonged, however it is constant in length unlike second degree AV block Mobitz Type I (Wenckebach) in which the PR interval progressively lengthens until a P wave is not conducted.