3. The Law of Discordance
In a normal LBBB the ST segments should be isoelectric or go be in the
opposite (discordant) direction from the dominant part of the QRS
So typically in V1 the QRS is mainly negative and the ST segment in elevated.
This is normal for LBBB
In V6 the QRS is mainly positive and the ST segment is down. This is normal
for LBBB
4.
5. Modified Sgarbossa Criteria for diagnosing
STEMI in the presence of a LBBB
If there is concordant ST changes (ST segments in the
same direction as the dominant part of the QRS) or a
discordant ST elevation of greater than 1/4 of the
amplitude of the S wave.
A: Concordant STE ≥ 1mm (in any lead) = Most specific
for MI
B: Concordant STD ≥ 1mm in V1, V2, or V3 = Specific for
MI
C: Discordant STE > 0.25 S
