Second degree AV block electrocardiogram
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]
Electrocardiogram
Electrocardiographic Findings
Type I Second Degree AV Block
- Also called the Wenckebach phenomenon or Mobitz type I block
- Intermittent failure of the supraventricular impulse to be conducted to the ventricles, not every P wave is followed by a QRS
- There is progressive prolongation of the PR interval until a P wave is blocked
- Progressive shortening of the RR interval until a P wave is blocked
- The RR interval containing the blocked P wave is shorter than the sum of 2 PP intervals
- The increase in the PR interval is longest in the second conducted beat after the pause
- These rules may not be followed because of fluctuation in vagal tone and secondary to sinus arrhythmia.
- In patients with normal QRS width, the block is usually located in the AV node
- there is progressive prolongation of the AH interval until the blocked P wave occurs
- When it is associated with bundle branch block, the block may occur in the AV node, His bundle or the contralateral bundle branch
- in 75% the block is in the AV node
- in 25% it is infranodal