Why We Do What We Do: Left Bundle-Branch Block

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A 73 year old female walked into the ER and reports that she has been increasingly out of breath and having chest pain. An EKG is performed and a LBBB is noted on the EKG. An old EKG is pulled from the files and identifies that she previously did not have a bundle branch block. What are we to do? Are we to interpret the LBBB as an ST elevation myocardial infarction equivalent? Do we get Cardiology involved? What are the guidelines? Check out this article and read the commentary below:

Lack of association between left bundle branch block and acute myocardial infarction in symptomatic ED patients – Chang et al – AJEM 2009

The American College of Cardiology/AHA Guidelines as well as ACEP Guidelines currently recommends treating LBBB as a class 1 fibrinolytic therapy recommendation. Thus, this woman described above is either going to the cath lab or you are pushing thrombolytics. What is interesting about these recommendations is that they are based on studies that do not specify RBBB vs LBBB. Patients with new LBBB represent a very small population within the world of myocardial infarction, so the data that is available is very limited. One element most studies seem to agree upon is that patients with LBBB tend to be older and have more cardiac risk factors than those who have regular intraventricular conduction. This particular study above looks at LBBB as an observational cohort study (or in other words, we are just going to track different groups of people and see what their outcomes are going to be). Three cohorts were created: new or presumed new LBBB, old LBBB or no LBBB. Of 7937 patients, only 55 had new or presumed new LBBB (so that makes it rare). When looking at the main outcome, the rate of AMI, there was no difference between the 3 cohorts. The secondary outcome addressed the rate of revascularization, which did show a difference. Patients with new LBB were more likely revascularized and were more likely to have documented coronary artery disease.

How would I handle a case after reading this article? Guidelines are guidelines…but the winds of change are coming. I would definitely get Cardiology involved early and repeat EKGs. An evolving MI may demonstrate some of the Sgarbossa criteria, which are highly specific for myocardial infarction and should make one move a little faster to get the patient into an interventionalist’s hands.
Sgarbossa Criteria:
1. ST segment elevation >=1mm and concordant with QRS complex (score=5)
2. ST segment depression >= 1 mm in leads V¬1, V2 or V3 (score=3)
3. ST segment elevation >5mm and discordant QRS complex (score=2)

The higher the score, the more likely an infarct. We do know that from Wong et al (2005) that patients with ST segment changes associated with their LBBB (especially Sgarbossa criteria 1 or 2) have a higher 30-day mortality than LBBB with no segment changes. Of note, the Sgarbossa criteria have very poor sensitivity. Knowing that there is no difference in outcome between a new LBBB and no LBBB, especially when there are no ST segment changes does make me hesitate about calling the cath lab. Get cardiology involved to participate in that decision. If I am alone in the boonies, however…guidelines are guidelines…push the thrombolytic or get them to cath until those guidelines change.

1. Chang et al., Lack of Association with between left bundle-branch block and acute myocardial infarction in symptomatic patients, American Journal of Emergency Medicine (2009) 27, 916-921.
2. Sgarbossa et al., Electrocardiographic Diagnosis of Evolving Acute Myocardial Infarction in the presence of Left Bundle-Branch Block, NEJM 1996;334:481-7.
3. Wong et al. Patients with Prolonged Ischemic Chest Pain and Presumed-New Left Bundle Branch Block Have Heterogenous Outcomes Depending on the Presence of ST-segment Changes, J Am Coll Cardiol 2005;46:29-38.

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