This document discusses Wolff-Parkinson-White syndrome and different types of atrioventricular heart blocks. Wolff-Parkinson-White syndrome involves an accessory pathway that partially bypasses normal conduction between the atria and ventricles, leading to a wide QRS complex on EKG. There are different types of AV heart blocks including first, second (Mobitz types I and II), and third-degree blocks, classified based on conduction patterns and relationships between P waves and QRS complexes. Mobitz type I block shows progressive PR interval prolongation while type II shows sudden conduction failure. Third-degree block shows no conduction between atria and ventricles.

1. Wolff-Parkinson-White and
Atrioventricular (AV) Heart
Blocks
Chapters 12 and 17

2. Wolff-Parkinson-White
Chapter 12

3. Artrioventricular Bypass Tract
Accessory pathways form
and fail to disappear
during fetal development
Formed near the mitral
or tricuspid valves or
interventricular septum
An AV bypass tract is
sometimes referred to as
the bundle of Kent

4. Artrioventricular Bypass
Tract
From SA node directly to
AV node AND to
ventricular myocardium
Partially bypassing the
bundle of His and purkinje
fibers

5. Accessory Pathways

7. Wolff-White-Parkinson
Wide QRS
due to early depolarization
not due to a delay in
depolarization
Shortened PR interval
Upstroke QRS complex is slurred;
delta wave

12. Wolff-Parkinson-White
As a general rule: the initial QRS
complex (delta wave) vector will point
away from the area of the ventricles that
is first to be stimulated by the bypass
tract
F.Y.I.

13. Wolff-Parkinson-White
Bypass Tracts
Left Lateral
negative delta waves in I and/or aVL and positive in V1
Posterior
positive delta waves in most of the precordial (chest) leads
and negative in the inferior leads
Right
negative delta waves in V1 and V2 and positive in I and
V6
Anteroseptal (anterior)
negative delta waves in leads V1 and V2
F.Y.I.

14. WPW Significance
More prone to arrhythmias especially
SVT
Often mistaken for RBBB or LBBB or an
MI

15. AV Heart Block
Chapter 17
15

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

17. First Degree Block
note the prolonged PR interval

18. Second Degree AV Block
Mobitz type I or Winckebach
Mobitz type II

19. Second Degree AV Block
Type I or Wenckebach

20. Second Degree AV Block
Type I or Wenckebach
1.Progressive lengthening of the PR
interval from beat to beat until a beat is
dropped.
2.The PR interval after the nonconducted
P wave is shorter than the PR interval
before the nonconducted P wave.
3.May be grouping of QRS complexes

22. Second Degree AV Block
Type II
1. Sudden appearance of a single, non-
conducted sinus P wave...
2. ...without...
1. ...the progressive prolongation of the PR
intervals…
2. ...and the shortening of the PR interval in
the beat after the non-conducted P wave.

23. Second Degree AV Block
Type II

24. 2:1 AV Blocks
• Often are type II blocks
• look for slightly prolonged QRS
• But they can be type I blocks
• look at long rhythm strip
• Sometimes they are labeled a “second
degree block” only

25. Advanced Second-Degree AV Block
• Two or more consecutive non-conducted sinus P
waves
• Note the consistent PR intervals

26. Third-Degree (Complete) AV Block

27. Third-Degree (Complete) AV Block
1. P waves are present, with a regular atrial
rate faster than the ventricular rate
2. QRS complexes are present, with a slow
(usually fixed) ventricular rate
3. The P wave bears no relation to the QRS
complexes, and the PR intervals are
completely variable
4. (Some properly timed P waves may be
conducted)

28. Third-Degree (Complete) AV
Block
• QRS can be normal width or wide

29. AV Dissociation
• SA is pacing the atria
• AV is pacing the ventricles
• Ventricular rate is similar to atria rate
• No P wave, even if properly timed, will
be conducted.

30. AV Dissociation

31. AV Dissociation

32. Third-Degree (Complete) AV Block

33. 100 b/min
42 b/min
No
Complete heart block