Second degree heart block - Mobitz type 2

Most beats are conducted with a constant PR interval. Occasionally there is an atrial contraction without a subsequent ventricular contraction, i.e. there is intermittent blocking of conduction either through the AV node or, more commonly, the His-Purkinje system. Disease of the His-Purkinje system is most often associated with a prolonged QRS duration.


Features of this ECG:

• Sinus rhythm, 90 b.p.m., normal QRS axis
• Features of Mobitz type 2 AV block:
• The PR interval is constant
• The first and seventh P waves on the rhythm strip are not followed by a QRS complex

• Features of left ventricular hypertrophy:
• SV2 + RV5 > 35mm
• Widespread ST depression and T wave inversion

Clinical note:

• Permanent pacemaker inserted.

• Unlike Wenckebach, Mobitz type 2 is usually due to disease of His bundle rather than the AV node and if it progresses to CHB the escape rhythm tends to be slow with wide QRS complexes

Common causes of Mobitz type 2 AV block

• Degenerative disease of the conducting system
• Anteroseptal infarction