Once you’ve identified a RBBB on the 12 lead ECG, the next thing you want to do is determine whether or not you’re dealing with a normal RBBB or an abnormal RBBB (or new RBBB).
You may remember this graph from my previous post: Who benefits the most from reperfusion therapy?
It shows that patients with “new BBB” receive the most benefit in terms of lives saved per 1000 treated with fibrinolytics (based on the FTT Collaborate Group). We often here it claimed that patients with “new LBBB” receive the highest benefit from prompt reperfusion therapy, but it’s worth pointing out that the FTT Collaborative Group did not distinguish between LBBB and RBBB.
Generally speaking, RBBB does not mimic or obscure the ECG diagnosis of acute STEMI the way LBBB does. However, sometimes it can (remember the update to Funky Trouble-Looking RBBB with AMI).
So how do we know what’s “normal” for right bundle branch block? We use the concept of “appropriate T wave discordance”. This concept usually comes up in the context of discussing LBBB, but it’s also useful for RBBB (and paced rhythms, ventricular rhythms, non-specific IVCD, and so on).
For RBBB, the concept is that when the terminal deflection of the QRS complex is positive, the T wave should be negative. Likewise, when the terminal deflection is negative, the T wave should be positive.
You may recall this graph from my previous post: Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria – Part II.
Remember, the terminal deflection is the last deflection in the QRS complex.
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 combo-pads are applied, revealing the following heart rhythm.
A 12 lead ECG is captured.
Right bundle branch block – Part II