Generally speaking, right bundle branch block does not mimic or obscure the ECG diagnosis of acute STEMI the way left bundle branch block does.
But how do we know what’s “normal” for right bundle branch block? One of the things we consider is the rule of appropriate T-wave discordance.
This concept usually comes up in the context of discussing left bundle branch block, but it’s also useful for right bundle branch block — with a caveat!
With right bundle branch block the T-wave should be deflected opposite the terminal deflection of the QRS complex.
In other words, when the terminal deflection of the QRS complex is positive, the T wave should be negative, and when the terminal deflection is negative, the T wave should be positive.
That’s a little bit different from left bundle branch block where we use the majority of the QRS complex as opposed to the terminal deflection.
The blue and red arrows show the expected relationship between the terminal deflection and the T wave with RBBB.
Consider the following case.
EMS is contacted for a 77 year old male complaining of chest pain. On arrival, you find the patient lying supine on the couch. He is ashen in color and diaphoretic with absent radial pulses. He responds sluggishly but appropriately and states that he is having severe sub-sternal chest pain.
His shirt is cut off and the combipads are applied, revealing the following heart rhythm.
It appears to be sinus rhythm with wide QRS complexes and occasional PVCs.
A 12-lead ECG is acquired.
Using the concept of “appropriate T wave discordance” is there anything about this ECG that bothers you?
Right bundle branch block: Part 2