Table 1: Criteria for Defining Left Bundle Branch Block.

Criteria	WHO (1985)[10]	Strauss Criteria (2011)[12]	ESC (2013)[13]	ACC/AHA/HRS (2018)[11]	ESC (2021)[13]
QRS duration	≥120 ms	≥140 ms (male), ≥130 ms (female)	≥120 ms	≥120 ms	≥120 ms
Lateral leads (I, aVL, V5 and V6)	Broad, notched or slurred R wave Absent Q wave in V5/V6	Broad notched or slurred R wave Broad notched or slurred mid-QRS ≥2 of leads V1, V2, V5, V6, I and aVL	Broad, notched or slurred R wave Absent Q wave in V5/V6	Broad notched or slurred R wave Absent Q wave in V5/V6	Notched or slurred mid-QRS in ≥2 of leads V1, V2, V5, V6, I and aVL Exclusive R-wave in I and aVL with negative asymmetrical T wave, slight ST depression and QS in aVR with positive T wave Unique R wave in V6 with negative T wave. When QRS is <140 ms, T wave may be positive
Precordial leads V1–V3		QS or rS in V1	QS or rS in V1	Small initial R waves	QS or rS in V1 with slightly elevated ST and positive asymmetrical T wave and unique R wave in V6 with negative T wave. When QRS is <140 ms, T wave may be positive
R peak time	≥60 ms in V5 or V6	-	-	≥60 ms in V5 or V6	-
ST segment and T wave	-	-	-	Positive concordance	ST segment is slightly opposed to the QRS polarity

ACC = American Heart Association; AHA = American College of Cardiology; ESC = European Society of Cardiology; HRS= Heart Rhythm Society.