This document discusses left bundle branch block (LBBB) in the context of acute myocardial infarction (AMI). It provides an overview of LBBB and challenges in diagnosing AMI when LBBB is present. Several criteria are discussed for identifying AMI in the setting of LBBB, including the original Sgarbossa criteria from 1996, modified Sgarbossa criteria from 2012, and the Barcelona algorithm from 2020. The Barcelona algorithm achieved the highest sensitivity while maintaining good specificity for diagnosing AMI when LBBB is present. An ECG example is also provided to demonstrate positive Sgarbossa criteria.

1. LEFT BUNDLE BRANCH BLOCK WITH
AMI

2. • Acute Myocardial Infarction (AMI) continues to be a
major cause of morbidity and mortality in Malaysia.
• With timely intervention and early reperfusion, the
cardiovascular outcomes have improved.
• The biggest challenge has been to reduce the total
ischaemic time, which is the time from onset of
chest pain till the time when the infarct related
artery is opened.
• A large portion of this delay has been the late
presentation of the patient with AMI to medical
attention (onset of chest pain to First Medical
Contact – FMC).
Despite this , in-hospital mortality remain high.
❏ Late presentation (lack of public awareness )
❏ Misdiagnosis (lack of our awareness )

4. STEMI EQUIVALENTS
Are those patients who do not present
with this classical ECG changes but
have acutely occluded coronary artery.
• They are often associated with poorer
outcome and worse prognosis.
• Benefit from timely intervention

5. 1- Wellens syndromes
2- de Winter syndrome
3- LBBB
4- ST elevation in lead AVR
5- Isolated posterior MI
Common STEMI EQUIVALENTS are :

6. 4.LBBB
Acute chest pain with LBBB can manifest in any of the
following 3 ways:
I. Commonest - LBBB but no pre-existing ECG.
II. LBBB and previous ECGs do not show LBBB.
III. LBBB and is known to have LBBB on old ECGs.
• New or presumably new LBBB has been considered a
STEMI equivalent (2004) until AHA guidelines 2013
• New LBBB should not be considered diagnostic of acute
MI in isolation

7. Left Bundle Branch Block LBBB
•Normally the septum is activated from left to right, producing small Q waves in the lateral
leads.
•In LBBB, the normal direction of septal depolarisation is reversed (becomes right to left), as the
impulse spreads first to the RV via the right bundle branch and then to the LV via the septum.
•This sequence of activation extends the QRS duration to > 120 ms and eliminates the
normal septal Q waves in the lateral leads.
•The overall direction of depolarisation (from right to left) produces tall R waves in the lateral
leads (I, V5-6) and deep S waves in the right precordial leads (V1-3), and usually leads to
left axis deviation.
•As the ventricles are activated sequentially (right, then left) rather than simultaneously, this
produces a broad or notched (‘M’-shaped) R wave in the lateral leads.

8. QRS Morphology Examples
•Lead aVL: ‘M’-shaped QRS complex
•Lead I: Notched R wave
•V6: Monophasic R wave
•V1: rS complex (tiny R wave, deep S wave) and
appropriate discordance (ST elevation and upright T wave)
•V5: RS complex
•V6: Monophasic R wave

9. CHALLENGING OF DIAGNOSING MI
IN LBBB
• Most cases of LBBB in suspected MI are not a result of focal infarction.
• Instead, extensive myocardial damage involving a large portion of the
distal conduction system is usually required to cause LBBB.
1. Septal Q waves indicative of an MI are absent as Left ventricular
activation is delayed in LBBB and the initial septal activation is from
right to left (opposite of the normal situation)
2. Secondary ST-T wave abnormalities that occur in LBBB obscure the
recognition of injury currents in ischemia and infarction.

10. In 1996 Sgarbossa et al : A total score of ≥ 3 is reported to have a specificity
of 90% for diagnosing myocardial infarction.
These criteria are specific, but not sensitive for myocardial infarction.
● 1. ST-elevation of ≥1 mm and concordant with the QRS complex (5
points).
● 2. ST-segment depression ≥1 mm in lead V1, V2, or V3 (3 points).
● 3. ST elevation ≥5 mm and discordant with the QRS complex (2
points).
In uncomplicated LBBB (without STEMI), the ST segment should be in the
opposite direction the majority of the QRS.
Any degree of ST segment elevation in a lead with a positive QRS
complex was a highly specific sign of acute myocardial infarction .
Leads V1-V3 always have predominantly negative QRS complexes, and
therefore ST segment depression should not be present, ST segment
depression ≥1 mm in just one of these leads is diagnostic of STEMI.

12. • ST-segment concordance with the QRS complex has a
specificity approaching 98% but with limited sensitivity (~20%)
Thus, the Sgarbossa criteria are informative if present
but not reassuring if absent and cannot be used to
exclude MI.
• In order to improve diagnostic accuracy, Smith et al. developed
the "modified Sgarbossa criteria," in which the original absolute
5 mm criterion is replaced with a proportion: ST elevation/S-
wave amplitude of ≤ -0.25).
• The authors reported improved diagnostic sensitivity from 52
to 91% in identifying angiographically proven MI but with
reduced specificity compared with the original Sgarbossa
criteria (90 vs. 98%).

14. CONCLUSION
• Less than half of all patients with suspected MI and LBBB ultimately will be diagnosed with an
MI.

15. 2012 – SW Smith modified the third component of the original criteria
from absolute (>5mm discordant ST elevation) to proportional (any ST segment
to S-wave ratio less than -0.25, with at least 1 mm ST elevation)
•≥ 1 lead with ≥1 mm of concordant ST elevation
•≥ 1 lead of V1-V3 with ≥ 1 mm of concordant ST depression
•≥ 1 lead anywhere with ≥ 1 mm STE and proportionally excessive discordant
STE, as defined by ≥ 25% of the depth of the preceding S-wave.
‘Replacement of the absolute ST-elevation measurement of greater than or
equal to 5 mm in the third component of the Sgarbossa rule with an ST/S ratio
less than -0.25 greatly improves diagnostic utility of the rule for STEMI.

16. Smith Modified Sgarbossa Criteria
The ST elevation/S wave amplitude ≤−0.25 (ST elevation ≥ 25% of the depth of
the preceding S wave).
In leads with a
predominantly
positive QRS
complex, this
criterion also
applies to ST
depression / R
wave amplitude
ratio.

17. PCI for LBBB in 3
situations:
1) Unstable patient
(hypotension,
pulmonary edema,
electrical instability)
2) The Sgarbossa
criteria satisfied (
score ≥ 3 points)
3) Smith Modified
Sgarbossa Criteria
Satisfied
Cai et al. diagnosis and triage algorithm

18. Proposed diagnosis and
treatment algorithm for
suspected myocardial
infarction and new left
bundle branch block with
results of retrospective
analysis of our database.
This hierarchical algorithm
approach yielded a high
sensitivity (97%) for the
identification of a culprit
coronary artery lesion,
although specificity (48%)

21. 2020: BARCELONA algorithm was introduced to improve the diagnostic sensitivity of ECG in patients with
LBBB and suspected AMI
• Sgarbossa rule of concordant ST depression in leads V1 to V3 was extended to any other lead
• The presence of an appreciable (≥1 mm or 0.1 mV) discordant ST deviation in low‐voltage QRS
complexes as in the absence of ischemia, these complexes usually show isoelectric ST‐segment
potentials and low‐voltage QRS are a frequent finding in patients with LBBB and AMI

23. ECG from a patient with acute myocardial infarction and culprit lesion in the right coronary artery,
showing ST‐segment depression ≥1 mm (0.1 mV) concordant with negative QRS polarity in lead V5.

24. ECG from a patient with acute myocardial infarction and culprit lesion in the left circumflex artery, showing
discordant ST deviation ≥1 mm (0.1 mV) in 2 leads with a QRS voltage ≤6 mm (0.6 mV).

25. ECG from a patient with acute myocardial infarction and culprit artery in the left main.Discordant ST deviation ≥1 mm
(0.1 mV) in leads with max (R|S) voltage ≤6 mm (0.6 mV) is present in leads III, aVR, and aVL.

26. CONCLUSION
The BARCELONA algorithm attained the highest sensitivity (95%), higher than Sgarbossa and
Modified Sgarbossa rules, while maintaining 89% specificity

27. ECG EXAMPLE

28. ● There is 1mm concordant ST elevation in aVL (= 5 points).
● Other features on this ECG that are abnormal in the context of LBBB (but not considered “positive”
Sgarbossa criteria) are the pathological Q wave in lead I and the concordant ST depression in the inferior
leads III and aVF.

29. Positive Sgarbossa criteria in a patient with LBBB and troponin-positive myocardial infarction:
•This patient presented with chest pain and had elevated cardiac enzymes.
•Baseline ECG showed typical LBBB.
•There is 1mm concordant ST elevation in aVL (= 5 points).
•Other features on this ECG that are abnormal in the context of LBBB (but not considered “positive”
Sgarbossa criteria) are the pathological Q wave in lead I and the concordant ST depression in the
inferior leads III and aVF.
•This constellation of abnormalities suggests to me that the patient was having a high lateral infarction.

30. REFERENCES
1. Dr. Smith’s ECG blog
2. Life In The Fast Lane ,Sgarbossa Criteria by Dr Mike Cadogan, last update
May 22, 2019
3. https://epmonthly.com/article/stemi-in-the-presence-of-lbbb/
4. LBBB in Patients With Suspected MI: An Evolving Paradigm
https://www.acc.org/latest-in-cardiology/articles/2017/02/28/14/10/lbbb-in-
patients-with-suspected-mi

31. THANK YOU