Second-Degree Atrioventricular (AV) Block Type II ECG Review

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.

2ndDegreeTypeIIAVBlockCriteria

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. A second-degree type II AV block indicates significant conduction disease in this His-Purkinje system and is irreversible (not subject to autonomic tone or AV blocking medications). This is a very important distinguishing factor compared to second-degree type I AV block. Because of this, a permament pacemaker is indicated in every patient with second-degree type II AV block.

ECG Examples:

References:

1. Surawicz B et al. ACC/AHA recommendations for the standardization and interpretation of the electrocardiogram. Circulation. 2009;119:e235-240.

2. Chou's Electrocardiography in Clinical Practice: Adult and Pediatric, 6e