In general, because LBBB alters the normal activation pattern of the left ventricle, it is said that you "can't interpret ischemia with a LBBB". But this is not quite correct. It is MORE difficult to do so, but if ischemic or infarction changes are present, they are likely real. In this EKG, there is ST elevation in leads 2 and F and a possible QS complex in these leads. Neither is 'normal' for a LBBB. In addition, T waves are in the same direction as the terminal deflections of the QRS in leads 2, 3,and F (and also V3-V6).
This is a PRIMARY repolarization abnormality suspicious for ischemia (remember that in BBB, the Tw axis should be opposite in direction from the main terminal deflection of the QRS. The Tw opposite to the terminal QRS is called secondary, because it is secondary to the BBB. Compare with a more typical LBBB.
The ST elevation in V1-V3 in today's EKG is typical for left bundle branch block and is NOT suggestive of ischemia (one reason why it is hard to read ischemia in LBBB). In short, this EKG is suspicious for an acute antero-inferior MI, despite the presence of the left bundle. NOTE: EKG's are for internal educational purposes of the University of Massachusetts Department of Family Medicine. Please do not forward without permission from Dr. Golding!
