C o m p e t e n c e i n E C G D i a g n o s e s

Lesson VI - ECG Conduction Abnormalities
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Wenckebach) and Type II AV block.
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In "classic" Type I (Wenckebach) AV block the PR interval gets longer (by
shorter increments) until a nonconducted P wave occurs. The RR interval of
the pause is less than the two preceding RR intervals, and the RR interval after
the pause is greater than the RR interval before the pause. These are the
classic rules of Wenckebach (atypical forms can occur). In Type II (Mobitz)
AV block the PR intervals are constant until a nonconducted P wave occurs.
There must be two consecutive constant PR intervals to diagnose Type II AV
block (i.e., if there is 2:1 AV block we can't be sure if its type I or II). The RR
interval of the pause is equal to the two preceding RR intervals.
Type I (Wenckebach) AV block (note the RR intervals in ms duration):
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Type I AV block is almost always located in the AV node,
which means that the QRS duration is usually narrow, unless
there is preexisting bundle branch disease.
Type II (Mobitz) AV block(note there are two consecutive constant PR
intervals before the blocked P wave):
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