ECG Blog #146 – (BBB – Primary ST-T Changes)

The ECG in Figure-1 was obtained from a patient with new-onset chest pain. It was interpreted as showing LBBB (Left Bundle Branch Block). As a result, the provider thought — “impossible to tell if anything acute is going on because there is LBBB”.

• Do you agree with that assessment?

Figure-1: 12-lead ECG from a patient with chest pain. How do you interpret this tracing?

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Clinical NOTE: In the past, it was thought that one could not diagnose an acute STEMI (ST Elevation Myocardial Infarction) in the presence of LBBB. This notion has been completely refuted. Although it will often be more difficult to diagnose acute ischemia/infarction in a patient with chest pain who presents in complete LBBB — in a surprising number of such patients, there will be at least strong suggestion on the initial ECG of acute STEMI despite the presence of underlying LBBB.

• When acute ECG changes in a patient with LBBB are subtle — diagnostic aids such as Smith-modified-Sgarbossa criteria may be helpful. At other times (such as for the ECG in Figure-1) — the diagnosis of acute STEMI is obvious without need to invoke modified Smith-Sgarbossa criteria. (NOTE: Search of Dr. Stephen Smith’s web site at the above link will provide numerous examples of how his criteria can be applied to clinical cases).

Interpretation of the ECG in Figure-1: The rhythm is sinus. The QRS complex is wide (≥0.12 second) — and QRS morphology is consistent with complete LBBB because there is a predominantly positive complex in lateral leads I and V6 — and, a predominantly negative QRS in lead V1. (For review of the Basics of BBB — Please see my ECG Blog #11). That said, there are a number of features that are distinctly atypical for simple LBBB. These include:

• i) The presence of septal Q waves in lateral leads I and aVL. Because the presence of LBBB alters the direction of initial septal activation (which can no longer proceed from left-to-right) — there should never normally be a septal q wave in a lateral lead when there is uncomplicated LBBB. The prominent Q waves in leads I and aVL of this tracing leave little doubt that infarction has occurred at some point in time.
• Beyond-the-Core: The presence of one or more lateral Q waves in association with LBBB do not indicate “lateral” infarction. Instead, they indicate septal and/or anteroseptal infarction — since the reason for their occurrence is that the LBBB has altered the direction of initial septal activation.
• ii) There is ST segment coving and primary ST elevation in lead aVL. This just shouldn’t be seen with typical LBBB. The most reliable way to recognize acute STEMI that occurs in association with LBBB is by the presence of frank ST elevation in a lead that should not show ST elevation. So, while it is admittedly challenging to determine if the anterior ST elevation that is seen in Figure-1 is a result of LBBB or acute anterior STEMI (because there is often some normal ST elevation in anterior leads with simple LBBB) — there should not be ST elevation in lateral or inferior leads.
• iii) There are reciprocal ST-T wave changes in each of the inferior leads. We know the inferior ST-T wave changes that are seen here are likely to be both real and acute — because these inferior ST-T wave changes are a “mirror-image” reflection of the ST-T wave in lead aVL. This reciprocal change picture shouldn’t be seen with uncomplicated LBBB.
• iv) The final abnormality occurs in the chest leads, and is indeed subtle — but it supports the above limb lead findings. That is, the ST segments in leads V5 and V6 are coved — and manifest a disproportionate amount of J-point ST depression (considering the modest amplitude of the R wave in these leads). This abnormal shape of the ST-T wave extends to lead V4. (We think there are also tiny-but-real q waves in lateral leads V5 and V6).

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Clinical Impression: In a patient with new-onset chest pain — the combination of the above findings should suggest an acute evolving STEMI until proven otherwise despite the presence of underlying LBBB.

• NOTE: Access to a prior ECG on this patient would clarify whether the LBBB in Figure-1 was new — and, would help to establish that the above noted changes are acute. But in the absence of a comparison tracing — the history (of new-onset chest pain) in this patient whose ECG shows LBBB with inappropriate lateral Q waves and primary ST-T wave changes despite the LBBB, should strongly suggest acute STEMI with need for immediate evaluation and reperfusion therapy until proven otherwise.

Follow-up: Unfortunately, the cardiac catheterization lab was not immediately activated for this patient. The patient coded in the hospital, and could not be resuscitated.

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Acknowledgment: My thanks to Casey Caldwell for allowing me to use this tracing and clinical case.

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Additional Material: For Review on ECG Diagnosis of the Bundle Branch Blocks — See my 17-minute ECG Video on this subject at www.bbbecg.com —

• Please note that if you click on SHOW MORE on the You-Tube page under where this video appears — You’ll see a detailed linked Contents that will allow you to immediately find whatever key points you are looking for in this video.