Friday, April 15, 2022

ECG Blog 298 — RBBB and Anything Else?

The patient is an elderly woman who presented to the ED (Emergency Department) with chest pain — and the ECG shown in Figure-1.  
  • There is RBBB (Right Bundle Branch Block). Is there anything else?

Figure-1: ECG from an elderly woman with chest pain (See text).

MY Initial Impression ( = the QuickVersion):

In the interest of conveying how fast we can arrive at a presumed diagnosis — Here is my “Quick Verson” assessment of today’s tracing:

  • The rhythm is sinus tachycardia at ~115/minute (ie, regular rhythm with upright sinus P waves in lead II).
  • The PR interval is normal — but the QRS is obviously prolonged (ie, clearly more than half a large box in duration = ≥0.11 second). BEST to “Stop!” one’s systematic approach as soon as QRS widening is recognized — in order to determine WHY the QRS is wide before proceeding further.
  • The typical RsR’ triphasic QRS complex in right-sided lead V1 with wide terminal S waves in lateral leads I and V6 is diagnostic of RBBB (Right Bundle Branch Block).
  • The predominantly negative QRS in each of the inferior leads is diagnostic of LAHB (Left Anterior HemiBlock).

NEXT: Now that we’ve determined WHY the QRS is wide in Figure-1 (ie, because of RBBB/LAHB) — I resumed my Rapid assessment:
  • Abnormal Q waves are seen in leads I and aVL (ie, these Q waves being clearly wider-than-they-should-be — given modest R wave amplitude in these leads).
  • Although the shape of the ST-T wave in lead V1 is typical for RBBB — it is definitely not typical in leads V2, V3 and V4. Instead — there is marked J point ST depression in leads V2, V3, V4 (which is maximal in lead V2) — followed by a distinctly abnormal straightening of the ST segment that rises slow (instead of initially descending, as it does for the ST-T wave in lead V1). This ST segment shape is characteristic of acute posterior OMI (Occlusion-based MI).

  • Looking at Other Leads: I do not see ST elevation in any leads. Instead — I see nonspecific ST-T wave flattening in most of the other leads.

  • IMPRESSION of ECG #1: Sinus tachycardia at ~115/minute. Bifascicular Block (ie, RBBB/LAHB). Abnormal high-lateral Q waves (in leads I, aVL). Acute posterior OMI until proven otherwise. The “culprit” artery with acute isolated posterior MI (or acute postero-lateral MI) — will most often be the LCx (Left Circumflex) coronary artery.



  • POINT #1: How do we know that the anterior ST depression in ECG #1 represents acute posterior MI — and is not simply from the RBBB?

ANSWER: the shape of ST depression that is normally seen in anterior leads with RBBB is slowly downsloping. It is not straightened, as seen in leads V2,V3,V4 of Figure-1
  • Even more specific to the diagnosis of posterior MI — ST depression from simple RBBB will decrease as you move from lead V1-to-V2-to-V3 — eventually disappearing as you move to more lateral chest leads. The depth of J-point ST segment depression should not increase as you move away from lead V1 — as it does in ECG #1 between lead V1 and lead V2. 
  • KEY Point: Acute posterior OMI is characterized by ST depression that is maximal in lead V2, V3 and/or V4 — just as is seen in ECG #1.


  • POINT #2: How do we know that the Q waves we see in leads I and aVL of ECG #1 are “pathologic” — and not simply normal septal q waves?

ANSWER: It is common to see small and narrow “normal septal q waves” in one or more lateral leads (ie, in leads I, aVL, V4,V5,V6). Complete RBBB does not eliminate these normal septal q waves.
  • Septal activation normally moves from the left-to-the-right side of the septum. Since the conduction defect with RBBB is on the right (not the left) side of the septum — the initial left-to-right vector of septal activation (during which time septal q waves are written) will remain intact with RBBB. 
  • How big is “too big” for a lateral q wave to be physiologic is hard to define. That said — in view of the acute situation for today’s case (ie, new chest pain in a patient with ongoing acute posterior OMI) — I interpreted the Q waves in both high-lateral leads (I, aVL) as being disproportionately tall and wide considering the very modest R wave amplitude in these leads. 
  • NOTE: It is common for the high-lateral wall to be involved with LCx lesions that cause acute posterior OMI.


  • POINT #3: How do we diagnose a Hemiblock when there is BBB (Bundle Branch Block)? 

ANSWER: The diagnosis of either LAHB or LPHB does not make sense when there is LBBB. In contrast — with RBBB, there can also be either LAHB or LPHB (in which case there will be a Bifascicular Block)
  • By definition, when there is LBBB — there is non-conduction through the left bundle branch system. As a result — there is impaired conduction through both the left anterior and left posterior hemifascicles. To say there is “LBBB plus LAHB” is therefore redundant (because "LBBB" already implies there is both LAHB and LPHB). 
As discussed in the ECG Videos in the Addendum below — the shortcut to diagnosis of the Bifascicular Blocks — is to realize that there are only 3 possible situations:
  • i) RBBB + LAHB (ie, in addition to RBBB — the QRS will be predominantly negative in each of the inferior leads). This is precisely the situation in today's tracing!
  • ii) RBBB + LPHB (ie, in addition to RBBB — the QRS in lead I will display a very steep and very deep S wave descent).
  • iii) RBBB without any hemiblock (ie, if neither lead I nor the inferior leads manifest predominant negativity).


Unfortunately — I lack details regarding specific management of this case beyond knowing that positive troponin confirmed acute infarction.
  • Given the older age of today's patient (and the lack of a prior tracing for comparison) — it is unknown whether the high-lateral Q waves and the RBBB/LAHB are "new" (this bifascicular block combination is more common with acute LAD rather than LCx occlusion).
  • Regardless — the "Take-Home" Message is that in a patient with new symptoms, today's ECG is absolutely diagnostic of acute posterior OMI.

Acknowledgment: My appreciation to M Shah (from Srinagar, India) for the case and this tracing.




Related ECG Blog Posts to Today’s Case:

  • ECG Blog #205 — Reviews my Systematic Approach to 12-lead ECG Interpretation.

  • ECG Blog #193 — illustrates use of the Mirror Test to facilitate recognition of acute Posterior MI. This blog post reviews the basics for predicting the "culprit" artery. (NOTE: Figure-2 in the Addendum below illustrates the essentials for identifying an isolated posterior MI).

  • ECG Blog #246 — for another example of acute Posterior MI (with positive Mirror Test).
  • ECG Blog #80 — reviews prediction of the "culprit" artery (and provides another case illustrating the Mirror Test for diagnosis of acute Posterior MI).
  • ECG Blog #285 — Reviews another acute Posterior MI.

  • ECG Blog #258 — How to "Date" an Infarction based on the initial ECG.

  • ECG Blog #204 — Reviews the ECG diagnosis of the Bundle Branch Blocks (RBBB/LBBB/IVCD). 
  • ECG Blog #203 — Reviews ECG diagnosis of Axis and the Hemiblocks. For review of QRS morphology with the Bifascicular Blocks (RBBB/LAHB; RBBB/LPHB).

  • ECG Blog #221 — Reviews a case of RBBB in the context of HOW to diagnose acute MI when there is BBB.

ADDENDUM (4/12/2022): 

I've added below selected media material that reviews KEY concepts related to today's case.


Figure-2: KEY points in the recognition of isolated posterior MI (This figure is taken from ECG Blog #193 — in which I review the "Basics" for predicting the "culprit" artery).


NOTE: For those who want a user-friendly video review illustrating how to diagnose the Bundle Branch Blocks in less than 5 seconds:

    ECG Media Pearl #22 (13:15 minutes Video) — ECG Blog #204 — Reviews a user-friendly approach for how to diagnose Bundle Branch Blocks (RBBB/LBBB/IVCD) in a matter of seconds! — also ECG Blog #282 —

    • CLICK HERE — for FREE download PDF of this 26-page file on BBB (from my ECG-2014-ePub) — with review on the Basics for ECG diagnosis of the Bundle Branch Blocks (including diagnosis of acute MI & LVH with BBB).


    ECG Media Pearl #21 (12:00 minutes Video) — ECG Blog #203 — User-friendly approach to the Hemiblocks (LAHB/LPHB) and Bifascicular Blocks (RBBB/LAHB- RBBB/LPHB).


    Today’s ECG Media PEARL #38 (11:30 minutes Audio)  Reviews the ECG Diagnosis of Acute MI when there is BBB.


    1. Hi Ken, thank you for this interesting case.
      In III we can see a r-wave higher ten the one in D2, do you think that according to LAFB it means a inferior involvment too?


      1. IF I understand your question correctly — my answer would be No. First — You are completely correct that it may be difficult to distinguish between LAHB with vs without associated inferior infarction. This is because, especially in today’s tracing — the initial vector of ventricular depolarization is traveling over the left posterior hemifascicle (since the anterior hemifascicle and the right bundle branch are blocked — and this posterior hemifascicle moves in an rightward and inferior direction. However with inferior infarction — the initial vector of ventricular depolarization will move AWAY from the inferior leads. Therefore, always difficult to assess what’s going on when there are opposing (potentially canceling out) forces. That said — I no Q waves in the inferior leads — and I see no “Q wave equivalents” (ie, notching in the initial r wave or in the S wave downslope in any inferior leads) — so I don’t thing relative height of the initial r wave in the inferior leads is specific for determining if there has or has not been inferior infarction. Hope the above makes sense. THANKS for your question! — :)