The traditional teaching (and pre-2013 ACC/AHA guidelines) for a new left bundle branch block (LBBB) on EKG (shown above) is that it is a STEMI equivalent and the cath lab should be activated. However, recent evidence in the last several years have shown that a new LBBB in and of itself is not indicative of new coronary occlusion.

So when should you suspect a STEMI in the setting of a new LBBB? Steve Smith (1) says that a new LBBB with Sgarbossa criteria met deserves a call to the cath lab. Amal Mattu (2) adds that if the patient is unstable or has acute heart failure with a new LBBB, consider that a STEMI equivalent.

A review of Sgarbossa criteria (needs 3 points):
ST elevation > 1mm in same direction as QRS (concordant)–5 points
ST depression > 1mm in same direction as QRS in V1, V2, V3–3 points
ST elevation > 5mm in opposite direction as QRS (discordant)–this by itself does not meet criteria as it is 2 points

Sgarbossa EKG from Rebel EM:


Also a great review of LBBB on Life in the Fast Lane (3).

1) Dr. Smith’s Blog:

2) Amal Mattu’s LBBB lecture: