Conduction delay:


AV block:


·     1st: all get through (↑PR interval)

·     2nd: some get through

o   Mobitz 1: progressive ↑PR then dropped QRS (Wenckebach)

o   Mobitz 2: dropped QRS at regular interval

o   2:1 block – could be Mobitz 1 or 2 (repeat the ECG)

·     3rd: none get through (a.k.a. complete heart block)

o   Junctional escape: narrow complex, rate 40-60

o   Ventricular escape: very wide complex, 20-40 (a.k.a. idioventricular)

o   P waves “marching through”


·     1st degree: only if very long

·     2nd degree Mobitz 1: if 3:1 or higher

o   Usually AV node problem (better)

·     2nd degree Mobitz 2: always

o   Usually His-Purkinje problem (worse)

·     3rd degree: always


Bundle branch block:

The fascicles

1.      Right bundle branch

2.      Left anterior fascicle       } Left bundle

3.      Left posterior fascicle     } branch

4.      AV node (only if trifascicular


·     LAFB: left axis deviation + qR laterally + rS inferiorly

·     LPFB: right axis deviation + rS laterally + qR inferiorly

Bundle branch block

·     LBBB: wide QRS, STEMI-like V1, ST depression + T inversion laterally

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·     RBBB: wide QRS, bunny ears, V1 (wide second ear)

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·     If unsure: the latter part of QRS is positive on the diseased side

o   LBBB: V6

o   RBBB: V1

Bifascicular block

·     RBBB + LAFB (look for it if left axis)

·     RBBB + LPFB (look for it if right axis)

Trifascicular block

·     AV block + RBBB + LAFB or LPFB

o   Incomplete: AV block 1st or 2nd degree

o   Complete: AV block 3rd degree


·     RBBB + LAFB + LPFB (a.k.a. complete heart block)


·     RBBB: often normal

·     LBBB: almost always abnormal

·     New LBBB = STEMI

·     Hemiblock: usually abnormal

·     Bifascicular block: PPM if syncope

·     Incomplete trifascicular block: PPM if syncope

·     Complete trifascicular block: PPM always