This document classifies and describes different types of atrioventricular heart block based on their conduction patterns. First degree block has a uniformly prolonged PR interval. Second degree block is divided into Mobitz type I, which has progressively prolonged PR intervals, and Mobitz type II, which has sudden conduction failure. Third degree block has no conduction between the atria and ventricles.

1. Atrioventricular (AV)
Heart Block
Chapter 17

2. Classification of AV
Heart Blocks
Degree AV Conduction Pattern
Uniformly prolonged PR
1 Degree Block
St
interval
Progressive PR interval
2nd Degree, Mobitz Type I
prolongation
2nd Degree, Mobitz Type II Sudden conduction failure
3rd Degree Block No AV conduction

3. First Degree Block
• prolonged PR interval

4. Second Degree AV
Block
• Mobitz type I or Winckebach
• Mobitz type II

5. Mobitz Type I

6. Mobitz Type I
• Progressive lengthening of the PR interval
from beat to beat until a beat is dropped.
• The PR interval after the nonconducted P
wave is shorter than the PR interval before
the nonconducted P wave.

7. Mobitz Type II

8. Mobitz Type II
• Sudden appearance of a single, non-
conducted sinus P wave...
• ...without...
• ...the progressive prolongation of the PR
intervals…
• ...and the shortening of the PR interval in
the beat after the nonconducted P wave.

9. Advanced Second-
Degree AV Block
Two or more consecutive nonconducted sinus P waves

10. Third-Degree
(Complete) AV Block

11. Third-Degree
(Complete) AV Block
• P waves are present, with a regular atrial
rate faster than the ventricular rate
• QRS complexes are present, with a flow
(usually fixed) ventricular rate
• The P wave bears no relation to the QRS
complexes, and the PR intervals are
completely variable