AV heart blocks can be caused by drug therapy, ischemic heart disease, degeneration due to age, aortic sclerosis, or cardiac surgery. First degree heart block involves slowed conduction through the AV node, prolonging the PR interval without dropped beats. Second degree heart block involves intermittent conduction, with Mobitz type I (Wenkebach) showing progressively prolonging PR intervals until a dropped beat, and Mobitz type II a constant PR interval with occasional dropped beats. Third degree heart block is a complete failure of AV node conduction, with dissociation between the P wave and QRS complex rates.

1. AV Heart Blocks
Rami AL-Khatib

2. AV Heart Blocks

3. Causes
• Drug therapy
• IHD (MI)
• Degeneration (age)
• Sclerosis (Aortic)
• Cardiac surgery

4. AV Node
• AV nodal conduction time is represented on
the ECG as the PR segment.
• P

5. First Degree Heart Block (1º)
• SA Node – normal
•Normal P wave
• AV Node conducts more slowly than
normal
•Prolonged constant PR Interval
• Rest of conduction is normal
•Normal QRS

6. First Degree Heart Block (1º)
• PR Interval > 0.2 seconds (5 small sq)
• Note – the PR Interval is constant

8. Significance
• Clinical significance
• None
• Treatment
• None
• Note – this can progress to 2º or 3º
heart block

9. Second Degree Heart Block (2º)
Types
• Mobitz Type I (Wenkebach)
• Mobitz Type II

10. Second Degree Heart Block (2º)
Mobitz Type I
(Wenkebach)
• Conduction through the AV Node –
progressively delayed until a drop beat
is seen
• Karl Wenkebach

11. Second Degree Heart Block (2º)
Mobitz Type I
(Wenkebach)
• PR Interval prolongs with each beat
until a dropped beat is seen.
• The PR Interval is NOT constant
• After each dropped beat, the PR
interval may be normal and the cycle
starts again.

12. Second Degree Heart Block (2º)
Mobitz Type I
(Wenkebach)
PR PR PR DROPPED BEAT

13. 2nd Degree AV block Mobitz 1

14. Significance
• Clinical Significance
•Slight symptoms
e.g. Lethargy, Confusion
• Treatment
•Pacemaker
• Note – this can progress to 3º Heart Block

15. Second Degree Heart Block
(2º)
Mobitz Type II
• Conduction through the AV node is
constant.
• PR interval is constant
• Occasionally more than one a dropped
beat is seen

16. Second Degree Heart Block
(2º)
Mobitz Type II
PR PR DROPPED BEAT PR

18. Significance
• Clinical significance – this is more
significant disease
• Treatment – pacemaker
• Note – this can progress to 3º Heart
Block

19. Third Degree Heart Block (3º)
(Complete)
• Complete failure of the AV Node
• No impulses from Sinus Node will pass
through to the ventricles
• Some part if the conducting system will
take over as pacemaker of the heart
(even a myocardial cell 10-15 bpm)

20. Third Degree Heart Block (3º)
(Complete)
• P wave rate – normal
• Ventricular rate – slow
• Ventricular complex may be broad
•Idioventricular rhythm
• Complete dissociation between P
waves & QRS

21. Third Degree Heart Block (3º)
(Complete)
P P P P P
QRS QRS

22. 3rd degree AV block

23. Significance
• clinical significance
•Symptoms LOC, Confusion,
Dizziness, Low BP
•Can lead to standstill, VT or VF
• Treatment - pacemaker

24. Summary
• 1º - prolongation of PR Interval & costant
• 2º - Mobitz I – Increasing PR Interval until dropped
beat is seen
• Mobitz II – Constant PR Interval with more P
waves to QRS
• 3º - Complete dissociation between P waves & QRS

25. References
• Hampton, J. R. (2013). The ECG made
easy. Elsevier Health Sciences.
• Hampton, J. R. (2013). 150 ECG problems.
Elsevier Health Sciences.
• O'Keefe Jr, J. H., Hammill, S. C., Freed,
M. S., & Pogwizd, S. M. (2010). The
complete guide to ECGs. Jones & Bartlett
Publishers.

26. Thank You