Written by Christian Gerhart
In non-ischemic right bundle branch block (RBBB) ECGs, we expect discordant ST depression and T wave inversions in leads V1-V3. ST segment elevation, or even an isoelectric ST segment, in these leads is abnormal and should make us concerned for ischemia. See below.
Be afraid of the RBBB
We continue to learn how the traditional STEMI paradigm fails to identify patients with occlusion myocardial infarction (OMI), thanks to the outstanding work of Drs. Steven Smith, Pendell Myers, and others. Interpreting EKGs in patients with abnormal conduction is challenging. We have previously learned that we can use the Smith-Modified Sgarbossa criteria for patients with left bundle branch block and ventricular-paced rhythms. But what about patients with RBBB?
This is a case of a patient with known coronary artery disease, a prior left anterior descending (LAD) artery drug-eluting stent, and a known RBBB who presented with chest pain. The ECG from the case is shown below. How would you manage this patient?
This ECG has ST elevation in leads V1-V3 (0.5 mm in V1, 1.5 mm in V2, and 1.0 mm in V3), which would not meet STEMI criteria. However, when this patient went to the cath lab, she was found to have in-stent restenosis of her LAD stent and an 85% occlusion of the first diagonal branch with TIMI-0 flow. Yikes!
Importantly, in RBBB, leads V1-V3 should have discordant (opposite the QRS) ST depression and T wave inversions. This is normal in RBBB. Any ST elevation in V1-V3 in RBBB, or even an isoelectric ST segment, in the setting of suspicious symptoms should raise concern for an LAD occlusion.
How will this change my practice?
I will be extremely vigilant when reading EKGs in symptomatic patients with RBBB. Findings of ischemia can be subtle and often do not meet STEMI criteria, even though patients may have an OMI.
Acute Coronary Occlusion in a Patient With Prior Known Right Bundle Branch Block: Another Chink in the Armor for the ST-Elevation Myocardial Infarction Criteria. Ann Emerg Med. 2023 Aug;82(2):219-221. doi: 10.1016/j.annemergmed.2022.12.006.