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2013 STEMI Guidelines: EMS is Accountable

11 comments

On Monday, the American College of Cardiology Foundation and the American Heart Association released the 2013 Guidelines for the Management of ST-Elevation Myocardial Infarction. Their last updates to these guidelines were in 2004 and 2006, so this is an important milestone.

If you have been following our blog and podcast, most of the changes will not be earth shattering. We have long been advocates of evidence based STEMI care, which has put us at the bleeding edge as the guidelines take time to catch up. What does this mean for you, our readers?

Our readers have been ahead of the game! We're constantly impressed by your breadth and depth of knowledge.

The 2013 guidelines makes these changes, which we've covered before, to the identification of STEMI:

The honest answer is we probably would not have written a post about these guidelines if it were not for the following gem, buried on page 10 in the section on Regional Systems of Care (emphasis mine):

"For patients who call 9-1-1, direct care begins with FMC, defined as the time at which the EMS provider arrives at the patient’s side. EMS personnel should be accountable for obtaining a prehospital ECG, making the diagnosis, activating the system, and deciding whether to transport the patient to a PCI-capable or non–PCI capable hospital."

Folks, a joint task force of cardiologists has just placed the responsibility for the diagnosis and activation of a STEMI in the hands of EMS providers!

Many systems are already ahead of the game when it comes to STEMI care, but others lag behind.

We've taken responsibility for the care of cardiac arrest victims and now is the time we acknowledge the critical role we play in STEMI care.

  • Does your system acknowledege paramedic diagnosis of STEMI?
  • Are you ready to take on the responsibility of diagnosis and activation of STEMI?
Posted by on December 20, 2012 • Filed under: ems-topics, patient-management, Training • Tagged: , , , , , , , ,

64 year old female CC: Trouble Breathing – Conclusion

13 comments

Lots of great comments and it was good to see the depth of discussion on the appropriate treatment and transport for this patient!

This is the conclusion to 64 year old female CC: Trouble Breathing.

When we left off our crew was attending to an elderly female patient in respiratory extremis. Pulmonary edema was present and their initial 12-Lead was concerning.

Many readers correctly noted the normal sinus rhythm, a 1° AV Block, and a wide QRS. Other readers pointed out the apparent Left Bundle Branch Block due to a negative QS complex in V1. Only a few readers picked up on the abnormal presentation of the LBBB: lead I has an rS complex and there is right axis deviation! Right axis deviation is a very uncommon finding in LBBB [1].

Just as it is important to know what a normal 12-Lead looks like, we also need to know what our abnormal 12-Leads should normally look like. In the case of LBBB, we expect V1 to be negative and leads I/V6 to have broad, monomorphic R-waves.

We also expect the T-waves to be discordant with the dominant deflection of the QRS. A picture is worth a thousand words in this case:

In our case we have three troubling findings:

  1. An rS complex in Lead I with Right Axis Deviation, which is very uncommon in LBBB.
  2. Concordant ST-segments in leads V5 and V6.
  3. Excessive ST-segement elevation in leads V2 through V4.

Many readers stated that a Left Bundle Branch Block is a STEMI mimic and precludes an activation of a STEMI alert until an old 12-Lead is used in comparison. However, criteria exists to diagnose a STEMI in the face of a LBBB or Paced rhythm.

Additionally, this patient's 12-Lead does not show a normal LBBB, but rather a non-specific intraventricular conduction defect or IVCD. Dr. Garcia would encourage, "considering the company it keeps," [2] which includes acute myocardial infarction!

Sgarbossa's criteria (and its modifications) for diagnosing STEMI in the face of LBBB or a Paced Rhythm has been covered in depth before so we'll only cover the positive criteria found on our 12-Lead:

  1. Is there ST-segment elevation ≥1 mm that is concordant with the QRS complex? Yes.

  2. Is there ST-segment depression ≥1 mm in leads V1, V2, or V3? No.
     
  3. Is there ST-segment elevation ≥5 mm, or ≥20% the depth of the S-wave, that is discordant with the QRS complex? Yes.

With 2 of the 3 criteria met (only 1 is required), we can be very confident that we're looking at a STEMI. Additionally, any concordant ST-elevation present should always suggest a STEMI.

The paramedic in this case recognized the concordant ST-elevation and the abnormal LBBB, called in a STEMI alert, and transported the patient to the PCI capable center. The patient improved significantly on the non-rebreather and CPAP was not necessary. Prior to arrival a second 12-Lead ECG was acquired:

Enroute the patient proved to be difficult for IV access, and received external jugular access in the ED. Labs were drawn while they waited for the cath lab team to arrive.

In the cath lab a 100% occlusion of the LAD was found and corrected with stenting.

For QA purposes an old ECG was retrieved after the call to compare to the field ECG:

Given this prior ECG, the new LBBB alone would likely cause a STEMI activation. However, in the absence of our more definitive changes this is a very weak criteria for activation [3].

Even without the prior ECG, we have an abnormal LBBB (most likely IVCD due to a peri-infarction block) with concordant ST-elevation and a patient presenting with signs of actue left sided heart failure: all of which point to an acute myocardial infarction!

This case highlights the importance of knowing what abnormal should normally look like and understanding that not every patient fits the protocol. We hope you enjoyed this case as much as we did, so be sure to continue the discussion below.

  1. Childers R, et al. Left bundle branch block and right axis deviation: a report of 36 cases. J Electrocardiol, 2000; 33 Suppl:93-102. [PubMed]
  2. The Art of Interpretation Series. http://www.12leadecg.com/
  3. Jain S, et al. Utility of left bundle branch block as a diagnostic criterion for acute myocardial infarction. Am J Cardiol, 2011; 107(8):1111-6. [PubMed]
Posted by on January 24, 2012 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , ,

80 year old male CC: Chest pain – Conclusion

22 comments

This is Part II of the conclusion to 80 year old male CC: Chest pain. For Part I see Excessive discordance as a marker of acute STEMI in LBBB.

First, let's take another look at the initial 12-lead ECG.

The first thing that catches my eye in this ECG is the strange morphology of the ST-segments and T-waves in the inferior leads (and lead aVL).

Could these be reciprocal changes to an acute anterior STEMI?

This ECG easily meets Sgarbossa's criterion of discordant ST-elevation > 5 mm, but is the ST-elevation excessively discordant when taking into account the depth of the S-wave?

Let's apply Dr. Smith's decision rule (that we learned about in the previous post). Do we see "excessive discordance" in this ECG?

Yes!

If this isn't evidence enough there are also significant changes in QRS voltage and ST/T morphology between the first and last 12-lead ECG.

Diagnosis: Acute anterior STEMI in the presence of LBBB.

See also:

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

Discordant ST-segment elevation in LBBB or paced rhythm

62 year old male CC: Chest pain

58 year old female CC: Chest pain

New left bundle branch block is a poor predictor of coronary occlusion (Dr. Smith's ECG Blog)

Posted by on December 29, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , , ,

Excessive discordance as a marker of acute STEMI in LBBB

17 comments

This is Part I of the conclusion to 80 year old male CC: Chest pain.

As we have discussed on numerous previous occasions, the expected relationship between the QRS complex and the ST-segment and T-wave in the setting of left bundle branch should be one of discordance.

This is sometimes referred to as the rule of appropriate T-wave discordance.

That means that in the setting of left bundle branch block, negatively deflected QRS complexes can be expected to show ST-elevation and upright T-waves.

Positively deflected QRS complexes can be expected to show ST-depression and inverted T-waves.

That's why left bundle branch block is an anterior STEMI mimic.

It is normal for the ST-segments to be deflected opposite the S-waves in the right precordial leads (V1-V3).

However, there is a limit to how much discordance is appropriate.

Sgarbossa's criteria requires at least 5 mm of discordant ST-elevation in order to be significant.

However, this criterion is problematic because it does not take into account the rule of proportionality.

That's why it's the weakest of Sgarbossa's critiera.

Discordant ST-elevation of 5 mm (as a stand-alone finding) only indicates a 50% probability of AMI according to Sgarbossa's original scoring algorithm.

 

This ECG from a previous case post demonstrates the dilemma.

 

The ST-elevation in leads V1-V3 is well over 5 mm but the S-waves are so deep that they are running off the bottom of the ECG paper.

This patient was not experiencing acute STEMI.

Stephen Smith, M.D. (of Dr. Smith's ECG Blog) uses a modified criterion which considers the ST/QRS ratio.

He has found that when the ST-segment is deviated more than 0.2 the QRS complex it is both a sensitive and specific marker for acute STEMI in the setting of left bundle branch block (and probably also paced rhythm).

(Note: This has since been revised to 0.25 the QRS (download PDF here). However, I still think it terms of allowing 1 mm of ST-elevation for every 5 mm of S-wave depth. When I do this, I round up. In other words, if the S-wave is 18 mm deep, I round up to 20, which means that I would allow up to 4 mm of ST-elevation in that lead.)

Let's examine each of these QRS complexes separately.

We'll start with the positively deflected QRS complex marked 'A'.

As you can see, the R-wave measures 10 mm. The J-point (relative to the PR segment) is depressed 3 mm. Therefore, the ST/QRS ratio is 0.3 (which is higher than 0.2). Hence, this finding would strongly suggest acute STEMI.

Now let's look at the negatively deflected QRS complex marked 'B'.

In this example the S-wave measures 10.5 mm. The J-point (relative to the PR segment) measures 3.5 mm. Therefore, the ST/QRS ratio is 0.33 (which is higher than 0.2). Hence, this finding, would strongly suggest acute STEMI.

In Part II we'll apply Dr. Smith's decision rule to the our recent case study.

See also:

80 year old male CC: Chest pain

80 year old male CC: Chest pain – Conclusion

Discordant ST-segment elevation in LBBB or paced rhythm

62 year old male CC: Chest pain

58 year old female CC: Chest pain

Posted by on December 29, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , , , ,

80 year old male CC: Chest pain

23 comments

Here’s a case submitted by a faithful reader who wishes to remain anonymous.

It’s a great case and destined to be one of my favorites!

EMS is called to evaluate a 80 year old male patient with a chief complaint of chest pain.

On arrival the patient is found sitting on his living room couch. He appears acutely ill and anxious.

Onset: 2 hours prior to EMS arrival
Provoke: Pain unrelieved after SL NTG x5
Quality: Severe substernal pressure
Radiate: The pain does not radiate
Severity: 8/10
Time: Several previous episodes but “never this bad”

Skin is cool, pale, and diaphoretic.

Breath sounds: clear

No JVD or peripheral edema noted.

Past medical history: CABG x3, CHF, angina, renal insufficiency, LBBB

Meds: Numerous but unavailable at the time of evaluation

Allergies: Penicillin

Vital signs:

RR: 20
Pulse: 108
BP: 150/80
SpO2: 99 on RA

The cardiac monitor is attached.

A 12-lead ECG is captured.

What is your impression?

*** UPDATE ***

Here are the serial 12-lead ECGs.

See also:

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

Discordant ST-segment elevation in LBBB or paced rhythm

62 year old male CC: Chest pain

58 year old female CC: Chest pain

Posted by on December 28, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , , , ,

58 year old female CC: Chest pain – Conclusion

9 comments

Here’s the conclusion to the 58 year old female with chest pain and left bundle branch block.

To refresh your memory here is the 12-lead ECG.

And for those of you who requested lead V4R.

This ECG meets all 3 of Sgarbossa’s criteria to identify acute STEMI in the presence of left bundle branch block.

Keep in mind, it only has to meet one criterion in one lead!

(Please note: One criterion has been modified from its original form. Instead of discordant ST-elevation > 5 mm we are looking for discordant ST-elevation > 0.2 the depth of the S-wave. This is known as the ST/QRS ratio. Credit to Dr. Smith of Dr. Smith’s ECG Blog.)

Angiography revealed 100% occlusion of the LCX and 99% occlusion of the RCA.

Thanks to everyone who commented on the case!

See also:

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

62 year old male CC: Chest pain (LBBB with ST-elevation > 0.2 the QRS complex)

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part I

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part II

“New” LBBB – What’s the big deal?

Discordant ST-segment elevation in LBBB or paced rhythm

Sgarbossa’s Criteria – New Graphic

Found on the Lifenet Receiving Station (LBBB with concordant ST-depression in leads V3 and V4)

Posted by on July 25, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , , ,

58 year old female CC: Chest pain

22 comments

Here’s another case study from an international reader who wishes to remain anonymous.

Presenting Complaint – Chest Pain

History of Present Complaint – 58 year old female, nil cardiac history, mild smoker, social drinker and overweight.

Complaining of acute central chest pain @ rest. Awoken by pain.

On Arrival – Sat upright on settee (Editor’s note: One of you Brits will have to interpret that for me!)

On examination:

Alert, orientated and communicable (GCS 15)
Pale, cool dry skin.

Nil SOB, clear bi-lateral air entry – nil adventitious breath sounds
R/R 19, SpO2 99%

H/R 68 and irregular, BP 125/74

Temp 36.8
B.M 7.2 (Editor’s note: B.M. is BGL measured in millimoles. 1 mmol/L of glucose is equivalent to 18 mg/dL. Hence, this patient’s sugar is about 130).

C/O chest pain.

O – Acute. Awoken from sleep.
P – Nothing makes pain better. Not affected by breathing
Q – Non specific compressing type pain
R – Central chest pain radiating left arm
S – Pain score 6/10
T – 30 mins
I – No pain intervention sought.

Slight nausea, nil vomit

The cardiac monitor is attached.

A 12-lead ECG is captured.

How would you treat this patient?

See also:

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

62 year old male CC: Chest pain (LBBB with ST-elevation > 0.2 the QRS complex)

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part I

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part II

“New” LBBB – What’s the big deal?

Discordant ST-segment elevation in LBBB or paced rhythm

Sgarbossa’s Criteria – New Graphic

Found on the Lifenet Receiving Station (LBBB with concordant ST-depression in leads V3 and V4)

Posted by on July 23, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , ,

62 year old male CC: Chest pain

10 comments

62 year old male presents to the emergency department complaining of chest discomfort.

Past medical history is significant for dyslipidemia and ulcerative colitis. Also prior history of significant tobacco use.

Maternal history of CAD. Maternal and paternal history of CVA.

The patient’s only medication is Lipitor but he took an aspinin en route to the hospital.

Onset: Patient states the pain started that morning and became progressively worse since lunch time
Provoke: Nothing makes the pain better or worse
Quality: Sharp and nonpleuritic
Radiate: The pain radiates down the right arm to the bicep
Severity: 7/10
Time: Patient states he experienced a similar pain in his right upper chest several days prior while playing tennis. He stopped exercising and the pain resolved.

The pain makes the patient feel “a little clammy.” He denies shortness of breath. He states that he feels “a little dizzy” but denies palpitations. He had a negative stress test 3-4 years ago.

He has a known history of left bundle branch block.

The patient’s skin is warm and dry.

Breath sounds clear bilaterally. No JVD. Neuro exam normal.

Vital signs:

Resp: 18
Pulse: 60
BP: 140/72
SpO2: 98 on RA

A 12-lead ECG is captured and presented to the ED physician within 5 minutes of arrival.

An “old” ECG is pulled from the computer system for comparison.

What is your impression?

*** UPDATE ***

After oxygen and nitroglycerin the patient reports a significant decrease in pain.

An additional 12-lead ECG is captured.

There is now slightly less ST-elevation in leads V3 and V4.

Remember that a secondary ST-segment abnormality (as opposed to a primary ST-segment abnormality) should not “improve” with oxygen and nitroglycerin!

In other words, if this ST-elevation was caused just by the LBBB, it shouldn’t be “getting better”. Changing ST-segments suggest the dynamic supply vs. demand characteristics of ACS!

Now, let’s go back to the initial 12-lead ECG. Is the ST-elevation in the anterior leads cause for concern?

Go back and read Identifying AMI in the presence of left bundle branch block (or paced rhythm).

Remember, discordant ST-elevation = or > 5 mm is the least specific of Sgarbossa’s criteria! That’s why we use the modified rule that I learned from Dr. Stephen Smith of Dr. Smith’s ECG Blog.

That criterion states that discordant ST-elevation should not be more than 0.2 (or 20%) the depth of the S-wave in the setting of left bundle branch block (ST/QRS ratio).

Using that criterion, how does this ECG measure up? Let’s take a look.

The patient was ultimately cathed and angiography revealed 100% occlusion of the LAD.

Final thought:

Does it get any more difficult that that? If Dr. Smith’s decision rule works this great, shouldn’t we be shouting it from the rooftops?

See also:

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part I

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part II

Discordant ST-segment elevation in LBBB or paced rhythm

Found on the Lifenet Receiving Station (LBBB with concordant ST-depression in leads V3 and V4)

58 year old female CC: Chest pain

58 year old female CC: Chest pain – Conclusion (meets all 3 of Sgarbossa’s criteria)

Posted by on May 19, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , ,

“New” LBBB – What’s the big deal?

13 comments

In the January 2010 EMCast at EMedHome.com, Amal Mattu MD reviews Chang AM, Shofer FS, Tabas JA, et al. Lack of association between left bundle-branch block and acute myocardial infarction in symptomatic ED patients. Am J Emerg Med 2009;27:916-921.

His comments confirm what I have suspected for a long time with regard to LBBB in the setting of suspected ACS.

“This is a really interesting and provocative article that may bust the traditional myth that we should be thrombolysing or cathing everybody with chest pain who presents with a new left bundle branch block.”

“They found that there was no significant difference in the rate of acute myocardial infarction between patients that were presenting with a new, or presumed new left bundle branch block pattern versus patients with a known old left bundle branch block pattern […] In other words, when patients presented with a new left bundle branch pattern, those patients did not rule-in at any greater increased frequency compared to the other patients, and based on this data the argument is certainly made that when patients have chest pain and they present with the left bundle branch block pattern, there’s not necessary a need purely based on the presence of a new left bundle to assume that that patient is having an acute MI, and therefore that patient needs to get thrombolytics or go immediately to the cath lab.”

“As I mentioned before, there is reasonable data to indicate that if the patient has a left bundle branch block – whether it’s new or old – and they demonstrate Sgarbossa criteria, then those patients do end up ruling-in for acute myocardial infarction […] Simple presence of a new left bundle branch block pattern does not appear to warrant immediate activation of the cath lab or immediate thrombolytics according to this study.”

Amal Mattu MD does add the caveat that the guidelines still state that patients with new LBBB are supposed to get reperfusion therapy.

See also:

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

58 year old female CC: Chest pain

58 year old female CC: Chest pain – Conclusion (meets all 3 of Sgarbossa’s criteria)

62 year old male CC: Chest pain (LBBB with ST-elevation > 0.2 the QRS complex)

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part I

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part II

Discordant ST-segment elevation in LBBB or paced rhythm

Sgarbossa’s Criteria – New Graphic

Found on the Lifenet Receiving Station (LBBB with concordant ST-depression in leads V3 and V4)

Posted by on January 11, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , ,

Sgarbossa’s Criteria – New Graphic

7 comments

Here is a graphic I created to help explain Sgarbossa’s criteria for identifying acute myocardial infarction (AMI) in the presence of left bundle branch block (LBBB) or paced rhythm.

In a previous article I showed this graphic which was created using PowerPoint.

Here is a similar graphic I created this morning by cropping actual ECGs that meet the criteria.


These are the features we should be looking for with LBBB and ventricular paced rhythms!

See also:

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part I

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part II

“New” LBBB – What’s the big deal?

Discordant ST-segment elevation in LBBB or paced rhythm

Found on the Lifenet Receiving Station (LBBB with concordant ST-depression in leads V3 and V4)

62 year old male CC: Chest pain (LBBB with ST-elevation > 0.2 the QRS complex)

58 year old female CC: Chest pain

58 year old female CC: Chest pain – Conclusion (meets all 3 of Sgarbossa’s criteria)

Posted by on January 3, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , ,

Found on the Lifenet Receiving Station

15 comments

Is there anything about this ECG (other than the poor data quality) that interests you?

The patient was a 90 year old male, fall with injury. Also complaining of pain between the shoulder blades.

*** UPDATE ***

This ECG caught my eye because it satisfies one of Sgarbossa’s criteria for the identification of AMI in the presence of LBBB. Specifically, the concordant ST-segment depression in lead V3 is a highly suspicious finding.

As a stand-alone finding, concordant ST-segment depression in a right precordial lead gives this ECG a score of 3 out of 10 (probability of AMI 66%).

I personally don’t think it’s necessary to score the ECG. As far as I’m concerned, an ECG that meets any of the criteria should be considered equivalent to an ECG showing acute STEMI, especially when you consider the depth of the S-wave in leads showing discordant ST-elevation (see previous posts on this issue).

So was this patient experiencing an acute STEMI? Here’s what I found out.

Patient (90 y.o.) arrived via EMS from XXXXXXXX after falling; there was no LOC, but did complain of back pain between the shoulder blades and diffuse abdominal pain. Extensive PMH: AAA, non-operable, HTN, CAD, CABG, LBBB, anemia, cardiomyopathy and dementia. The ED physician spoke to the daughter extensively who did not want her father worked up, but did consent to a thoracic x-ray and stated she only wanted him to receive pain medication and return transport to the XXXXXXXX and did not want any further diagnostics noting that his dementia worsens when he is out of his environment. He has a living will /advanced directive on file and with him a DNR order.

He was given pain medication in the ED, the thoracic film showed no acute injury and a prescription for Lortab was written and he was sent back to the nursing home. He did not have an EKG performed on this visit or any other diagnostics. The patient was here for an admission in 6/2009 and it appears that the EKGs are very similar.

Interesting!

When designing a STEMI program you have to make difficult choices when it comes to exclusion criteria like age, DNR status, and neurological status. Was this patient experiencing an acute thrombotic event in an epicardial coronary artery? I guess we’ll never know.

It’s possible this ECG finding was old and it’s possible it was secondary to aortic dissection or aneurysm.

See also:

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

58 year old female CC: Chest pain

58 year old female CC: Chest pain – Conclusion (meets all 3 of Sgarbossa’s criteria)

62 year old male CC: Chest pain (LBBB with ST-elevation > 0.2 the QRS complex)

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part I

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part II

“New” LBBB – What’s the big deal?

Discordant ST-segment elevation in LBBB or paced rhythm

Sgarbossa’s Criteria – New Graphic

Posted by on November 6, 2009 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , ,

Identifying STEMI in the presence of LBBB – Sgarbossa’s Criteria – Part II

9 comments

In Part I, we discussed Sgarbossa’s Criteria for identifying AMI in the presence of LBBB. We also talked about the “rule of appropriate T wave discordance” for bundle branch blocks and other forms of abnormal depolarization (like ventricular rhythms or paced rhythms).

You will recall that I drew a distinction between a QRS complex’s main deflection and its terminal deflection, even though they are one in the same for LBBB. I explained that it’s helpful to think in terms of the terminal deflection, because then you can apply the “rule of appropriate T wave discordance” to RBBB as well as LBBB.

And so you can!

Let’s look at an ECG.

This is from one of my “old” 12 lead ECG classes. In those days, I cropped the computer measurements and interpretive statements because I didn’t want the students to “cheat”. Nowadays, whether it’s EMS or firefighting, I’ve come to believe in reality-based training. In real life, for good or bad, you get an interpretive statement.

But, this ECG is a good example of an important concept.

So let’s look at this ECG. It’s a sinus rhythm. It has a normal axis. We know that for several reasons.

The QRS complex is smallest in lead aVL, so the perpendicular lead on the hexaxial reference system is lead II. Lead I is almost equiphasic so the perpendicular lead is aVF. The value of lead II is 60 degrees and the value of lead aVF is 90 degrees, so the frontal plane axis is somewhere between 60 and 90 degrees.

Or, to do it the “easy” way, lead I and lead aVF are both positively deflected, so we know we’re in the left inferior quadrant.

Or, because leads I, II, and III are all positive, so we know the axis is normal.

It really doesn’t matter what method you use. I use all three for every ECG.

The QRS duration is wide. When supraventricular rhythms are wide, we look at lead V1 to see if it shows RBBB or LBBB morphology. This ECG shows a terminal R wave in lead V1, which is RBBB morphology. Next we check lead I and look for a terminal S wave. We find one!

This is a simple RBBB.

You will notice that in many leads, the T wave is deflected the same direction as the QRS complex (II, III, aVR, aVF, V2, V3, V4, V5, and V6). In other leads, the T wave is deflected opposite the main deflection of the QRS complex (aVL, V1). I did not list lead I because the QRS complex is close to equiphasic.

So, how should these T waves be deflected?

The answer is, they should be deflected opposite the terminal deflection of the QRS complex, and so they are!

Look at the following image.

As you can see, when the terminal deflection of the QRS complex is negative, the T wave is positive. When the terminal deflection is positive, the T wave is negative. In other words, even if the main deflection of the QRS complex is positive, as long as the terminal deflection (or last deflection) is negative, the T wave is positive.

That’s why I’m encouraging you to always think in terms of the terminal deflection, even though for LBBB, the terminal deflection is also the main deflection.

There is method to this madness!

Although not part of Sgarbossa’s Criteria, the “rule of appropriate T wave discordance” can help you pick up on AMI in the setting of RBBB (or bifascicular block) because an inappropriately concordant ST segment and/or T wave can tip you off that something is wrong!

For example, this case from Dr. Smith’s ECG blog.

In the last lesson, we introduced Sgarbossa’s Criteria. Let’s take a look at a graphic that shows exactly what we’re looking for.

The first example shows > 1 mm of concordant ST segment elevation (and a concordant T wave). Both are abnormal for LBBB.

The second example shows > 5 mm of discordant ST segment elevation and a discordant T wave. Discordant ST segment elevation > 5 mm is abnormal for LBBB (with one very important caveat) but a discordant T wave is normal for LBBB!

In the last example, there is concordant ST segment depression in the right precordial leads, which is abnormal for LBBB, but a discordant T wave, which is normal for LBBB.

If you have a patient with signs and symptoms consistent with ACS and the ECG shows LBBB with concordant ST segment elevation, then chances are excellent that you are dealing with a STEMI.

Likewise, if you have a patient with signs and symptoms consistent with ACS and the ECG shows LBBB with concordant ST segment depression, especially in the right precordial leads, then chances are excellent that you are dealing with a STEMI.

The original criteria didn’t take into account the depth of the S wave, and as we know from other STE-mimics like LVH, the deeper the S wave, the higher the ST segment elevation. So a blanket statement that 5 mm of discordant ST segment elevation indicates acute STEMI in the setting of LBBB is not helpful in those situations where the S wave is > 50 mm deep like the example below.

Stephen Smith, M.D. of Dr. Smith’s ECG Blog has suggested that a more sensitive and specific marker is discordant ST-elevation > 0.2 the depth of the S wave (ST/QRS ratio).

See also:

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part I

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

“New” LBBB – What’s the big deal?

Sgarbossa’s Criteria – New Graphic

Discordant ST-segment elevation in LBBB or paced rhythm

Found on the Lifenet Receiving Station (LBBB with concordant ST-depression in leads V3 and V4)

62 year old male CC: Chest pain (LBBB with ST-elevation > 0.2 the QRS complex)

58 year old female CC: Chest pain

58 year old female CC: Chest pain – Conclusion (meets all 3 of Sgarbossa’s criteria)

Posted by on December 15, 2008 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , , , ,

Identifying STEMI in the presence of LBBB – Sgarbossa’s Criteria – Part I

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There has been a lot of discussion lately about identifying AMI in the presence of LBBB (see Dr. Bearemy’s “My Emergency Medicine Blog” here and a recent thread on the EKG Club). I’ve also been receiving a lot of emails offlist, so I think a full discussion is in order.

In my recent post Who benefits the most from reperfusion therapy? I posted a graph that demonstrates how patients with new bundle branch block benefit the most from reperfusion therapy.

*** Important Update ***

Recent evidence suggests that new (meaning previously undetected) LBBB patients do not “rule-in” for AMI at any greater rate than any other group of patients! That’s why it’s so important for health care practitioners to understand Sgarbossa’s criteria! Those are the patients who need immediate reperfusion therapy in the cardiac cath lab!

*** End Update ***

The problem is that in many prehospital 12 lead programs (and regional STEMI systems), patients with LBBB or a QRS duration > 0.12 sec (120 ms) are excluded! In other words, patients with wide QRS are taken to the local community hospital without interventional capability. Or, the cath lab is not activated while EMS is still in the field.

Why would you exclude the very patients who stand to benefit the most from prompt, expertly performed PCI at a cardiac center?

Simple.

It’s too difficult to figure out whether or not the BBB is new! The ECG diagnosis of STEMI can be difficult in the setting of BBB.

In False Positive Cardiac Cath Lab Activations I reviewed Larson, Menssen, Sharkey et all, False-Positive” Cardiac Catheterization Laboratory Activation Among Patients With Suspected ST-Segment Elevation Myocardial Infarction, JAMA 2007;298(23):2754-2760.

I quoted:

Patients with new or presumably new left bundle-branch block had an inordinately high prevalence of false positive catheterization laboratory activation (almost half did not have a culprit artery). Patients with a previous myocardial infarction or previous coronary bypass surgery had a significantly higher prevalence of no culprit artery, likely because of abnormal baseline ECG results.

This is obviously a big problem, and subjecting all patients with LBBB and signs and symptoms of ACS to an emergent cath or the risks associated with thrombolytic therapy is not the answer, as some authors have suggested.

If only there was some kind of algorithm that could help distinguish between patients with LBBB and acute STEMI from patients with LBBB who are not experiencing acute STEMI.

But there is such an algorithm! It’s been around for over 10 years!

The GUSTO investigators Sgarbossa et al., Electrocardiographic Diagnosis of Evolving Acute Myocardial Infarction in the Presence of Left Bundle-Branch Block. N Eng J Med 1996; 334(8):481-487 published an algorithm which has come to be known as “Sgarbossa’s Criteria”.

The criteria seems complicated but it’s really not. Like anything else, it’s a tool. A very important tool for a critical subset of patients.

The original paper contains a flow chart from which the patient receives a score. I’m not going to publish the flow chart, because it’s not something you need to memorize.

Here is the criteria. A patient is presumed to be experiencing an evolving AMI if any of the following are present.

  1. ST segment elevation = or > 1 mm that is concordant with the QRS complex.
  2. ST segment depression = or > 1 mm in leads V1, V2, or V3.
  3. ST segment elevation = or > 5 mm that is discordant with the QRS complex.

It is the last criterion that has caused the most controversy and requires qualification.

However, before we address the third criterion, we have to dispose of a common misunderstanding.

What do we mean by concordant and discordant? The short answer is, concordant means “the same direction” and discordant means “the opposite direction”.

The rule of appropriate T wave discordance

In the presence of abnormal ventricular depolarization (left bundle branch block, right bundle branch block, paced rhythm, ventricular rhythms) the T wave should be deflected opposite the terminal deflection of the QRS complex (appropriate T wave discordance).

What is the terminal deflection?

The terminal deflection is the last deflection, or wave, of a QRS complex.

Please take the time to learn this! It is extremely important!

Take a look at the following image.

You will notice that each of these QRS complexes is labeled according to the waves are present. If the wave is large, it gets a capital letter. If the wave is comparatively small, it gets a lowercase letter.

I could talk about this image for a long time, but for now, I just want you to notice that an Rs complex is positively deflected while an rS complex is negatively deflected, even though both of them contain only an R and an S wave. But the terminal deflection of each is negative, because they both end in an S wave!

Why is this important?

When teaching Sgarbossa’s Criteria, students always get confused as to whether or not the ST segments and T waves should be deflected opposite the main deflection of the QRS complex or opposite the terminal deflection.

Well, guess what?

With LBBB, the terminal deflection is the main deflection!

So why are we splitting hairs?

Because if you learn to think in terms of the terminal deflection, you can use the rule of appropriate T wave discordance for RBBB, too!

Let’s start by looking at a patient with a normal LBBB.

I have no idea why the GE-Marquette 12SL interpretive algorithm is giving the “data quality prohibits interpretation” message for this ECG. There’s a little bit of artifact in the inferior leads, but it’s not that bad!

This is a normal looking LBBB. We know the frontal plane axis is around 0 degrees, because the QRS complex is isoelectric in lead aVF. Therefore, the perpendicular lead in the hexaxial reference system is lead I. Since lead I is positively deflected, we can place the frontal plane axis at 0 degrees. A physiological left axis deviation (0 to -30) is normal for left bundle branch block.

To put it another way, a negative QRS complex in lead III is normal for LBBB, but it should be upright and monomorphic in lead I.

Now, let’s look at the QRS complexes and the T waves.

You will notice that in every lead, the T wave is deflected opposite the QRS complex! This is “appropriate T wave discordance” in the presence of left bundle branch block.

To help illustrate this point, consider the following graphic.

The blue arrow shows the direction of the terminal deflection of the QRS complex (which is also the main deflection in the setting of LBBB). The red arrows shows the direction of the ST segment and the T wave.

This is what we mean by “appropriate T wave (and ST segment) discordance” with LBBB. Note that with RBBB, the T wave should be discordant, but the ST segment should remain isoelectric. This is why RBBB is usually not listed as a STE-mimic.

With LBBB, there is also a discordant shift of the ST segment, which is why it’s one of the most common STE-mimics! ST segment elevation in the right precordial leads (V1-V3) is a normal finding for LBBB!

In Part II, we’ll look at the “rule of appropriate T wave discordance” as it applies to RBBB and talk more about Sgarbossa’s Criteria.

See also:

Identifying AMI in the presence of LBBB – Sgarbossa’s Criteria Part II

80 year old male CC: Chest pain

Excessive discordance as a marker of acute STEMI in LBBB

80 year old male CC: Chest pain – Conclusion

“New” LBBB – What’s the big deal?

Sgarbossa’s Criteria – New Graphic

Discordant ST-segment elevation in LBBB or paced rhythm

Found on the Lifenet Receiving Station (LBBB with concordant ST-depression in leads V3 and V4)

62 year old male CC: Chest pain (LBBB with ST-elevation > 0.2 the QRS complex)

58 year old female CC: Chest pain

58 year old female CC: Chest pain – Conclusion (meets all 3 of Sgarbossa’s criteria)

Posted by on December 13, 2008 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , , , , , , , ,