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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