LBBB as a STEMI Mimic
Example: LBBB with Secondary T-wave Changes
We explicitly listed the criteria for the LBBB in the last topic. It was also noted that secondary T-wave changes are expected and we frequently will see T-wave inversion as a part and parcel of the LBBB pattern.
Looking at the above ECG tracing. It is important to note that another common finding in the LBBB pattern is ST-segment elevation (CONCAVE DOWN) in lead V1, V2, V3 as well as Q-waves in lead V1, V2, (not unlike our observation of the LVH pattern). One would ordinarily associate this with an acute MI; but, in the case of the LBBB, it simply represents the expected waveshape.
The important point to remember here is that in the setting of the LBBB, the ST-segment is so distorted that it is extremely difficult to make the diagnosis of the acute MI (and in fact CANNOT be made with certainty; except with utilization of the Sgarbossa Criteria – discussion upcoming).
With this in mind, it is advised that if the diagnosis of LBBB is made, you should ONLY comment on secondary or primary T-wave changes. Otherwise, you should NOT attempt to analyze the ST-T changes any further as regards infarction or ischemia (except when looking for the STEMI).*
This misinterpretation of the pseudoinfarction pattern of the LBBB is one of the most common pitfalls of electrocardiography as well as is the pseudoinfarction pattern associated with the LVH pattern.
*The student must know that this discussion and conclusion does NOT hold true for the RBBB. In particular, the acute MI MIGHT BE seen as ST-segment elevation in the Associated leads and depression in the Reciprocal leads in the setting of the RBBB.
For a discussion on the Modified Sgarbossa Criteria and diagnosing STEMI in the presence of the LBBB….
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