The Modified Sgarbossa Criteria: Diagnosing STEMI in the presence of the LBBB (or Pacemaker Rhythm)
The Acute STEMI can be recognized according to the Modified Sgarbossa Criteria as follows in the discussion below.
As a member of the STEMI team of your hospital you have been asked to interpret the ECG of Figure 1 of a 75 year old female with chest pain. Is this a STEMI? Would you mobilize the cardiac cath lab?
Figure 1 75 Year Old Female with Chest Pain
DISCUSSION
Analyzing this tracing with the acronym H*E*A*R*T will reveal an LBBB pattern. It is well known that the LBBB is fraught with S T-T changes that mimic/mask the acute MI/ischemia. We therefore must proceed with caution as we search for the elusive acute STEMI.
We have previously noted that the ST-T signals in the LBBB and RBBB conform to the following rule:
SECONDARY ST-T CHANGES (also known as DISCORDANT)
If the terminal portion of the QRS complex is negative →→→→→→→ ST segment is elevated/T-wave is upright or biphasic.
If the terminal protion of the QRS complex is positive →→→→→→→ ST segment is depressed/T-wave is inverted or biphasic.
This is referred to as secondary ST-T changes of the LBBB. It is important to emphasize that these ST-T changes are the norm (unless they are excessively discordant as described below) and DO NOT suggest infarction/ischemia!
PRIMARY ST-T CHANGES (also known as CONCORDANT)
During your dissection of the LBBB pattern you will occasionally encounter the following in some of the leads:
If the terminal portion of the QRS complex is negative →→→ ST segment is depressed/T-wave inverted or biphasic.
If the terminal portion of the QRS complex is positive →→→ ST segment is elevated/T -wave upright or biphasic.
This polarity is in stark contrast to those we have labeled as secondary ST-T changes.
This finding is consistent with myocardial infarction/ischemia and is described as primary ST-T changes of the LBBB.
A further refinement of the ST-T changes associated with infarction/ischemia of the LBBB is as follows:
DIAGNOSTIC CHANGES OF THE STEMI (IN PRESENCE OF LBBB; also applies to the pacemaker rhythm)
Although it is often challenging, please know that the acute STEMI can be diagnosed in the presence of the LBBB pattern.
The criteria is as follows: (as outlined by E.B. Sgarbossa et al. and S.W. Smith)
MODIFIED SGARBOSSA CRITERIA
You only need one lead to satisfy the following criteria of the Acute STEMI: *
*As per always you must correlate clinically and compare with the old tracing if available.
STEP Ι.
Only need one lead of the 12-leads (includes Lead avR) to demonstrate:
≥ 1 mm of concordant ST elevation (J-Point elevation)
Figure 2. Concordant ST Elevation.
OR
STEP ΙΙ.
≥ 1 mm concordant ST depression in Leads V1 or V2 or V3.
Figure 3. Concordant ST Depression in Leads V1 or V2 or V3.
OR
STEP ΙΙΙ.
≥ 1 mm excessively discordant ST elevation in any lead.
Figure 4. Excessively Discordant ST Elevation.
Excessively discordant is defined as ST-elevation that is ≥ 25% of the depth of S-wave i.e.
J / S ≥ 0.25 Excessively Discordant
Using the measurements from Figure 4, let us calculate the ratio of J/S.
Please realize that the ST-elevation in this tracing is not of concern per se, but it is the amount of elevation compared with the depth of the S-wave, ie the ST- elevation is secondary to the LBBB, but the question becomes.
Is it excessive compared to the depth of the S-wave?
To answer this, let us do the simple math. Measuring to the nearest 1/2 mm we get
J ≅ 25 mm
S ≅ 55 mm
now taking the ratio J/S = 25/55 ≅ 0.45
This clearly far exceeds 0.25 and if this were found in a given tracing →→→→ it is a STEMI.
Note:
- PR – segment serves as baseline. (some practitioners use the baseline as the TP-segment)
- ST-elevation (measured at J-point) is distance from J-point to baseline.
(Some practitioners measure ST segment elevation as distance from a point on the ST segment as measured 60 ms [1.5 mm] after J-point to the baseline.)
A SYSTEMATIC -ANALYTICAL APPROACH
When evaluating the ACS patient with an LBBB (or RV pacemaker Rhythm) you should analyze the tracing as follows (one step at a time):
STEP Ι.
Systematically scan all 12 leads (including avR) looking for any concordant ST elevation ≥ 1 mm. (it only takes one)
If present in any lead →→→ it is a STEMI.
If absent →→→ continue on as follows.
or
STEP ΙΙ.
Look at Leads V1,V2,V3 looking for concordant ST depression ≥ 1mm.
If present in any of V1V2V3 →→→ it is a STEMI.
If absent →→→ continue on as follows.
or
STEP ΙΙΙ.
Systematically scan all 12-leads looking for “excessively discordant ” ST elevation ≥ 1 mm, i.e. measure J on each lead with ST elevation, then measure the corresponding S-wave depth.
Calculate the quotient J/S.
This quotient should be < 0.25 (25 %)
If not (even in one lead) →→→ it is a STEMI.
If none of the above is found →→→ it is NOT a STEMI (At least not cardiographically speaking. Don’t forget about the possibility of false positives and false negatives.)
Please remember that many MI patients in the emergency unit will have only minimal non-specific ST-T changes. Serial tracings(as often as every 10 minutes), serial cardiac markers and clinical correlation will ultimately give the diagnosis.
That said, the Modified Sgarbossa Criteria possesses high specificity for the STEMI i.e. with these findings (if coinciding with your clinical suspicion), you should mobilize the cardiac cath team.
Now let us return to the tracing of Figure 1 and apply the Modified Sgarbossa Criteria to it.
Figure 1. 75 Year Old Female with Chest Pain.
STEP Ι.
Systematically scan all 12 Leads looking for ST-elevation ≥ 1 mm concordant with the QRS complex ….this is a eureka moment…
Please look at Lead III and note:
a…..The terminal portion of the QRS complex is positive.
b…..The J-point is elevated > 1mm (ST-segment is concave down)
Therefore, this is an Acute STEMI (concordant ST-elevation; concordant ST -elevation is also noted in Lead avF) .
No further analysis needed. You should mobilize the cardiac cath team if the clinical findings are consistent with ACS.
Now let us analyze one more LBBB as shown in Figure 2 below. The clinical setting is a 69 year old male with chest pain. No old tracing is available.
Does this represent an acute STEMI?
Figure 2 LBBB Tracing of 69 year old male with chest pain.
First when you apply the H*E*A*R*T acronym you will conclude that it is a LBBB pattern. We now know that we must decide that the tracing satisfies the Modified Sgarbossa Criteria or it does not.
If it does….it is a STEMI
If it does not….cardiographically speaking, it is not a STEMI
SYSTEMATIC ANALYSIS of this tracing
STEP Ι
Systematically look at all 12 Leads looking for concordant ST elevation ≥ 1 mm.
It is absent →→→ Therefore continue.
STEP ΙΙ
Look at V1,V2,V3 looking for concordant ST depression.
It is absent →→→ Therefore continue.
STEP ΙΙΙ
Now look at all 12 Leads looking for “excessively discordant” ST elevations ≥ 1 mm. ( this can be a laborious task since you must analyze each of the 12 leads – one at a time – measuring the ratio J/S).
We know that the term “excessively discordant” refers to the ratio of J/S and that this ratio should not be as large as 0.25 (25%).
If it is (only takes one lead)→→→ it is a STEMI
If it is not →→→ it is not a STEMI
Our task now is to calculate the J/S ratio of each lead with ST elevation. For illustrative purposes I have chosen to analyze Lead V3.
The approximate measurements (rounded off to the nearest 1/2 mm) are as follows:
J ≅ 4.5 mm
S ≅ 36.5 mm
Now calculate the ratio:
J/S ≅ 4.5/36.5 ≅ 0.123
This is well within the safety zone of < 0.25.
you can then proceed to analyze the next Lead, then the next, then the next, then the next (with ST elevation) and calculate its J/S ratio.
You will find that all the J/S s will be < 0.25 →→→ Therefore this tracing is not a STEMI.
The interpretation of this tracing is LBBB with secondary T-wave changes. The disposition plan of the patient would be determined by the clinical correlation, old tracing comparison, lab, x-ray etc. As always, we treat the patient – not the cardiogram!
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