Great example by Dawn of RBBB with ECG signs of recent acute MI. I'll add several points to Dawn's description:

    Although it is more difficult to assess acute ischemia/infarction in the setting of QRS widening from BBB (Bundle Branch Block) - it will nevertheless be possible to do so in many cases. It is definitely easier to assess ischemia/infarction with RBBB than with LBBB. This has an anatomic & physiologic basis.

• The initial part of the ventricles to be activation is the LEFT SIDE of the SEPTUM. Septal activation normally goes left-to-right. When there is LBBB - this direction of initial septal activation is altered (since the left bundle goes down the left side of the septum). Consequently - septal activation has to go from right-to-left when there is LBBB. You are therefore CHANGING the direction of the INITIAL ventricular activation with LBBB. Since Q waves are written during this initial ventricular activation period - detection of Q waves is far more difficult when there is LBBB ...
• In contrast - the direction of initial ventricular activation is UNCHANGED when there is RBBB. This is because the right bundle branch goes down the right side of the septum. RBBB does not affect inital septal depolarization that still moves from left-to-right. As a result - you usually CAN see infarction Q waves with RBBB.
• So it is with this tracing. We see large anterior Q waves (in V1,2,3) despite the RBBB. We have lost the rSR' in V1 (replaced with a QR) - but as per Dawn, we still recognize RBBB by QRS widening, the QR in V1 and the wide terminal S waves in lateral leads.
• Had I not known the history in this patient - I would have interpreted this tracing as, "Sinus rhythm; RBBB; Anterior MI of uncertain age - possibly acute". The ST-T wave in lead V1 is consistent with RBBB and not particularly suspicious of acute infarction. But in addition to ST segment coving in leads V2,V3 - there IS suggestion of ST elevation in these leads (esp. in view of the fact that the ST segment should be BELOW the baseline slanting downwards if the only thing occurring was RBBB).
• ST-T wave appearance is also distinctly abnormal in lead V4 - with coving and suggestion of recent injury (consistent with the ST-T waves in V2,V3).