Know what a normal LBBB “looks” like
- QRS duration of > 120 ms
- Negative QRS Complex in V1
- Positive QRS Complex in lateral leads (I, aVL, V5-V6)
LBBB causes a repolarization abnormality
Consider a “repol” abnormality when there is a “general pattern of ST discordance”, meaning the ST segment opposite the QRS in nearly every lead (can be caused by LVH, LBBB, WPW, etc.).
In a LBBB there is normally ST elevation in leads with a negative QRS at baseline.
2013 AHA STEMI Guidelines
“New or presumably new LBBB has been considered a STEMI equivalent. Most cases of LBBB at time of presentation, however, are “not known to be old” because of prior electrocardiogram (ECG) is not available for comparison. New or presumably new LBBB at presentation occurs infrequently, may interfere with ST-elevation analysis, and should not be considered diagnostic of acute myocardial infarction (MI) in isolation”.
- New or presumed new LBBB does not predict an MI
- MI occurs at similar frequencies between patients with a new LBBB, an old LBBB, and patients without a LBBB
- Patients with a LBBB frequently have an unequivocal STEMI diagnosis go unrecognized because clinicians aren’t familiar with how to diagnose an MI in this setting
Criteria for diagnosing STEMI in a LBBB
Standard Sgarbossa Criteria
1) ST-segment elevation ≥1 mm concordant with the QRS complex in any lead (5 points)
2) ST-segment depression ≥1 mm in lead V1, V2, or V3 (3 points)
3) ST-segment elevation ≥5 mm discordant with the QRS complex in any lead (2 points)
Smith Modified Sgarbossa Criteria
Excessive Discordance in Patient with a Paced Rhythm
There’s obvious discordant ST elevation in the inferior leads (>50%). Although the computer cropped the S wave in V1, there’s probably excessive discordance and a “straight” ST segment indicating a probable right ventricular infarction.
Excessive Discordance in a LBBB
Again, obvious ST elevation this time noted in the anterior leads. Clearly excessively discordant and ST/S almost more than 50%. This was not appreciated the transporting Paramedic or ER Physician!
Time for the podcast!
Chang, A. M., Shofer, F. S., Tabas, J. A., Magid, D. J., McCusker, C. M., & Hollander, J. E. (2009). Lack of association between left bundle-branch block and acute myocardial infarction in symptomatic ED patients. The American Journal of Emergency Medicine, 27(8), 916–921. https://doi.org/10.1016/j.ajem.2008.07.007
Das, D., & McGrath, B. M. (2016). Sgarbossa criteria for acute myocardial infarction. CMAJ. https://doi.org/10.1503/cmaj.150195
Gregg, R. E., Helfenbein, E. D., & Babaeizadeh, S. (2013). New ST-segment elevation myocardial infarction criteria for left bundle branch block based on QRS area. Journal of Electrocardiology. https://doi.org/10.1016/j.jelectrocard.2013.07.001
Hanna, E. B., Lathia, V. N., Ali, M., & Deschamps, E. H. (2015). New or presumably new left bundle branch block in patients with suspected acute coronary syndrome: Clinical, echocardiographic, and electrocardiographic features from a single-center registry. Journal of Electrocardiology, 48(4), 505–511. https://doi.org/10.1016/j.jelectrocard.2015.04.011
Neeland, I. J., Kontos, M. C., & De Lemos, J. A. (2012). Evolving considerations in the management of patients with left bundle branch block and suspected myocardial infarction. Journal of the American College of Cardiology. https://doi.org/10.1016/j.jacc.2012.02.054
O’Gara, P. T., Kushner, F. G., Ascheim, D. D., Casey, D. E., Chung, M. K., De Lemos, J. A., … Zhao, D. X. (2013). 2013 ACCF/AHA guideline for the management of st-elevation myocardial infarction: A report of the American college of cardiology foundation/american heart association task force on practice guidelines. Journal of the American College of Cardiology. https://doi.org/10.1016/j.jacc.2012.11.019
Sefa, N., & Sawyer, K. N. (2016). Smith-Modified Sgarbossa Criteria and Paced Rhythms: A Case Report. Journal of Emergency Medicine, 51(5), 584–588. https://doi.org/10.1016/j.jemermed.2016.06.055
Sgarbossa, E. B., Pinski, S. L., Barbagelata, a, Underwood, D. a, Gates, K. B., Topol, E. J., … Wagner, G. S. (1996). Electrocardiographic diagnosis of evolving acute myocardial infarction in the presence of left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase and Tissue Plasminogen Activator for Occluded Coronary Arteries) Investigators. The New England Journal of Medicine, 334(8), 481–487. https://doi.org/10.1056/NEJM199602223340801
Sgarbossa, E. B., Pinski, S. L., Barbagelata, A., Underwood, D. A., Gates, K. B., Topol, E. J., … Wagner, G. S. (1996). Electrocardiographic Diagnosis of Evolving Acute Myocardial Infarction in the Presence of Left Bundle-Branch Block. New England Journal of Medicine, 334(8), 481–487. https://doi.org/10.1056/NEJM199602223340801
Smith, S. W., Dodd, K. W., Henry, T. D., Dvorak, D. M., & Pearce, L. A. (2012). Diagnosis of ST-elevation myocardial infarction in the presence of left bundle branch block with the ST-elevation to S-wave ratio in a modified sgarbossa rule. Annals of Emergency Medicine, 60(6), 766–776. https://doi.org/10.1016/j.annemergmed.2012.07.119
Tabas, J. A., Rodriguez, R. M., Seligman, H. K., & Goldschlager, N. F. (2008). Electrocardiographic Criteria for Detecting Acute Myocardial Infarction in Patients With Left Bundle Branch Block: A Meta-analysis. Annals of Emergency Medicine. https://doi.org/10.1016/j.annemergmed.2007.12.006