cardiolab logocardiolab

2nd Degree AV Block

caution
Lead II
25 mm/s10 mm/mV
Heart rate
72bpm
RR
833ms
QT
358ms
Type

2nd Degree Type II (Mobitz)

Intermittent failure of conduction below the AV node (at the bundle of His or bundle branches). Unlike Wenckebach, the PR interval is constant — beats drop without warning.

Mechanism

Intermittent failure of conduction below the AV node (at the bundle of His or bundle branches). Unlike Wenckebach, the PR interval is constant — beats drop without warning.

Findings· 3
  • Fixed PR interval for conducted beats.
  • Sudden dropped QRS without prior PR prolongation.
  • QRS is often wide (bundle branch block pattern).
Clinical Impact

Dangerous. High risk of progression to complete heart block without warning. Usually requires permanent pacemaker implantation regardless of symptoms.

Differential· 2
Mobitz Type I

Both drop QRS complexes. Mobitz I has progressive PR lengthening; Mobitz II has constant PR.

Complete Heart Block

Mobitz II can progress to complete block. Look for total AV dissociation in 3rd degree.