Left bundle branch block (LBBB) can be identified by changes in the electrocardiogram (ECG).


Features of LBBB:

(1) duration of QRS >= 0.12 seconds (120 milliseconds)

(2) V5 and V6 show

(2a) either a broad, monophasic R wave or an RS complex

(2b) absence of Q waves

(3) lead I shows a broad, monophasic R wave


Additional findings that may be present:

(1) left axis deviation

(2) poor R wave progression from V1 to V6

(3) displacement of ST segment and T wave in a direction opposite to the dominant deflection of the QRS complex (appropriate discordance)


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