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65 year old male CC: Fall with injury – Conclusion

10 comments

This is the conclusion to 65 year old male CC: Fall with injury. You may wish to review the history and clinical presentation.

When we left off the patient was in severe heart failure with the following 12-lead ECG.

As we have mentioned before on several occasions, the most important thing when treating a patient with a tachycardia is to decide whether or not the tachycardia is causing the symptoms or the symptoms are causing the tachycardia.

In other words, you should try to rule out the possibility that it's a compensatory tachycardia. As this case clearly demonstrates, this can be very difficult! 

The crew felt that the differential diagnosis for this wide complex tachycardia (from most likely to least likely) was VT, 2:1 atrial flutter with LBBB, sinus tachycardia with LBBB, or some other SVT with aberrancy.

Due to the patient's instability, the treating paramedic felt there was little to lose and much to gain by attempting synchronized cardioversion. If the rhythm was VT or 2:1 flutter the patient's condition might improve dramatically. If it turned out to be sinus tachycardia with LBBB he'd be in the exact same position.

Attempt #1

Attempt #2

There appeared to be no change in the heart rhythm.

A report was given to online medical control and the patient was transported emergently to the hospital.

On arrival the patient was placed on BiPAP and started on a NTG drip.

Here was the 12-lead ECG on arrival.

The patient was given lopressor 5 mg slow IV push.

The conversion rhythm shows sinus rhythm at 92 bpm with left bundle branch block.

So, we now know that the patient probably had LBBB at baseline. However, without a heart rate histogram it's difficult to say whether or not this was 2:1 flutter that converted sinus rhythm or sinus tachycardia that was slowed down with the lopressor.

This is often overlooked in the emergency setting but in the inhospital setting it's very important to document the onset or termination of an arrhythmia for this very reason.

The patient's SpO2 came up above 90% and the patient became more alert and was attempting to communicate by the time EMS was done writing their report. No further information is available.

Posted by on July 2, 2012 • Filed under: ems-topics, patient-management • 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: , , , , , , , , , , , , ,

29 year old female: Unresponsive – Conclusion

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This is the conclusion to 29 year old female: Unresponsive.

To recap, our patient overdosed on an unknown quantity of unknown medications. She is hypotensive and firefighters are maintaining her airway with an OPA and assisting ventilations with a BVM. She has a history of suicide attempts and was found down in her grandmother's home, who recently passed away.

Before we cover our patient's rhythm, it is important that we ensure our patient's ABC's are being appropriately managed. In this case, given the patient is deeply unresponsive we should consider placement of an advanced airway. If transport time is short, consideration should be given to continuing BLS airway maintenance.

She is also hypotensive, so while our patient is being preoxygenated–which is not the same as hyperventilated–we can work to establish IV or IO access. Our crew in this case used this approach, establishing a large bore IV while the firefighters ventilated the patient. Shortly after access was acquired, her SaO2 had risen to 98% and she was intubated without diffuculty.

With her ABC's covered, we can take a look at her initial rhythm:

At a first look, the complexes are wide and this could be a fast irregular rhythm or even a bigeminal rhythm. Closer inspection reveals regular P-waves with a slightly prolonged PRi and a 1:1 association with the QRS complexes.

The QRS complexes are wide and we may have wide premature complexes following them. However, these apparent PVC's fall during the absolute refractory period and therefore must be T-waves. Hyperkalemia is a strong possibility. This is a normal sinus rhythm with a 1st Degree AV Block, a wide QRS, and a prolonged QTc.

If the rhythm strip did not have you taking a second look at the T-waves, the 12-Lead ECG certainly did. They tower over the QRS complexes and a symmetrical and peaked. A left bundle branch block is present and the axis is normal.

At this point we need to strongly consider what medications our patient may have ingested. Most field providers should be knowledgable with the common medications geriatric patients are prescribed, especially those being treated for depression. We should be concerned for an acute overdose of one or more of the following:

  • Narcotics
  • Tricyclic antidepressants
  • Antiarrhythmics (including beta and calcium channel blockers)
  • Diuretics
  • Oral hypoglycemics

As many readers pointed out, this case is likely a tricyclic overdose, but it does not have all of the classic ECG signs. Present are many of the sodium channel blocking effects, including a prolonged PRi, widened QRS, and prolonged QTc. However, missing are the rightward terminal axis and the anticholenergic-like tachycardia. Because of this combination, often times the presenting rhythm is a bizarre wide complex tachycardia.

The rightward terminal axis in a TCA overdose manifests itself as slurred S-waves in multiple leads and a characteristic large R wave in aVR as seen in the figure below:

The crew in this case elected to treat for suspected tricyclic and potentially a concurrent narcotic overdose. They administered 2 L of normal saline, 1 mg naloxone, and 100 mEq of sodium bicarbonate. An OG tube was placed but not used. At the ED, a tox screen was positive for tricyclic antidepressants and barbiturates. Lab values were not available to the crew.

Polypharmacy overdose presents a challenge to both pre-hospital and hospital providers. Rapid intervention in the face of incomplete information is often necessary and the ECG can provide key information to guide treatments.

The ECG can neither unequivocally rule in nor rule out impending toxicity; recognizing these limitations, the emergency [providers] can use this bedside tool in combination with other clinical data during the assessment of the poisoned patient. -Harrigan and Brady
Posted by on October 10, 2011 • Filed under: ems-topics, patient-management • Tagged: , , , , , , ,

88 year old female CC: Chest pain – Conclusion

4 comments

This is the conclusion to 88 year old male CC: Chest pain.

Let's take another look at the 12-lead ECG.

This ECG shows acute STEMI in the presence of left bundle branch block.

It's also an excellent example of the value of using "excessive discordance" to identify acute STEMI in the presence of left bundle branch block.

For a more extensive discussion of this topic see:

Excessive discordance as a marker of acute STEMI in LBBB

First, let's see if we can make the case for acute STEMI using Sgarbossa's original criteria.

As a refresher, here are Sgarbossa's criteria to identify AMI in the presence of LBBB

1.) ≥ 1 mm of concordant ST-elevation (in the same direction as the majority of the QRS complex) in at least one lead
2.) ≥ 1 mm of ST-depression in lead V1, V2 or V3
3.) ≥ 5 mm of discordant ST-elevation (opposite the majority of the QRS complex) in at least one lead

According to the original scoring algorithm, the more of these criteria that are met, the higher the probability of AMI.

 

So, let's apply these criteria to this case.

Do we see ST-elevation that is concordant with the majority of the QRS complex in at least one lead?

This criterion appears to be met in lead II.

Do we see ST-depression in leads V1, V2 or V3?

Possibly. I bring up data quality so often on this blog that I probably sound like a broken record, but it's rare that I run a case study where we don't have to compensate for poor data quality in one way or another. In this case it appears that ST-depression may be present in lead V1.

How about discordant ST-elevation = or > 5 mm?

This finding is absent on this 12-lead ECG. However, it doesn't really matter because this finding is (by far) the least specific of Sgarbossa's criteria. It's the least specific because it doesn't take into account the depth of the S-wave (rule of proportionality).

In other words, the deeper the S-wave, the greater the ST-elevation, and this is normal.

That's why we use the modified criterion proposed by Stephen Smith, M.D. (Dr. Smith's ECG Blog).

Rather than look for ST-elevation that is = or > 5 mm, we look for ST-elevation that is > than 0.2 (or 1/5) the depth of the S-wave!

To put this in a quick "rule of thumb" for you, for every 5 mm of S-wave depth, we allow 1 mm of ST-elevation.

Or, you can break out the calipers and calculate the ST/QRS ratio.

Let's apply the modified criterion to this case.

Do we see any leads with a ST/QRS ratio > 0.2?

We certainly do (and it's not even close).

So, lead II meets one of Sgarbossa's original criteria (concordant ST-elevation = or > 1 mm) while leads III and aVF meet Smith's modified criterion (ST/QRS ratio > 0.2).

This is more than enough evidence to call this an acute inferior STEMI in the presence of LBBB.

But we aren't finished yet!

Smith et al. discovered that "excessive discordance" works for positive and negative QRS complexes!

With this in mind, do we see "excessive discordance" anywhere else in this ECG?

Yes we do! Lead aVL shows ST-depression that is "excessively discordant" with the QRS complex.

Is lead aVL reciprocal to leads II, III and aVF?

Yes it is.

Point, game and match.

BTW, I also made the calculations for lead V4 because it looked close to me.

It was close, but no cigar. So take a good look at lead V4! This shows close to the maximum ST-elevation that is permitted for a QRS complex of this size.

Once you train your eye it's much easier to spot excessive discordance!

See also:

80 year old male CC: Chest pain

58 year old female CC: Chest pain

Posted by on May 1, 2011 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , ,

An unusual case of left bundle branch block – Discussion

8 comments

This is a follow-up discussion to an usual case of left bundle branch block (60 year old male CC: Shortness of breath).

Let’s take another look at the 12-lead ECG.

It turns out this patient was experiencing a STEMI.

However, the 12-lead ECG doesn’t meet any of the typical criteria for acute STEMI in the presence of left bundle branch block (if indeed this is a left bundle branch block).

While it’s a supraventricular rhythm with a QRS duration > 120 ms and shows LBBB morphology in lead V1, there are S-waves in leads I and V6. Hence, you could argue that this is a nonspecific intraventricular conduction defect.

Having said that, there is something strange about the ST-segments in this ECG.

Normally when faced with a left bundle branch block I consider the “rule of T-wave discordance”.

With a left bundle branch block, that means that the T-wave (and ST-segment) should be deflected opposite the QRS complex.

But what about qR, rS or Rs complexes in the presence of left bundle branch block?

Should the ST/T-wave be deflected opposite the majority of the QRS complex or the terminal deflection?

Opinions are divided on this point but I use the terminal deflection.

Let’s look at lead aVR for this case.

You will note that the ST-segment and T-wave are deflected in the same direction as the terminal deflection of the QRS complex. That makes it concordant (bad).

Now let’s look at the inferior leads.

I would consider this to be concordant ST-depression.

How let’s look at leads V5 and V6.

Even though these are RS complexes and almost equiphasic, the ST-depression is in the same direction as the terminal deflection. Again, I would consider this to be concordant (bad).

So, we have ST-elevation in lead aVR and ST-depression in the inferior and lateral leads.

There also appears to be less ST-elevation than we would normally expect in the right precordial leads, but it’s hard to say definitively due to the wandering baseline and the fact that the S-waves are “cut off” in leads V2 and V3.

It reminds me a little bit of the previous case 63 year old male CC: Chest pain.

Let’s take a look at that 12-lead ECG.

Here the QRS duration is only 116 ms (not quite a bundle branch block) but there is ST-elevation in lead aVR and ST-depression in the inferior, lateral and anterior leads.

The patient was experiencing an acute left main coronary occlusion.

Again, this was a tough case, and I can’t say that it was diagnostic for acute STEMI, but it wasn’t “normal” looking either.

EMRAPTV Episode 68: aVR Gets No Respect!

Life in the Fast Lane … Another Widow Maker?

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 (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

Posted by on February 2, 2011 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , ,

An unusual case of left bundle branch block (60 year old male CC: Shortness of breath)

11 comments

Here’s a really interesting case submission from David Baumrind.

EMS is called out in a rain storm to evaluate a 60 year old male with a chief complaint of shortness of breath.

The patient was released from the rehab center 8 days prior after having experienced a stroke while having his “carotids done”.

He suffers from persistent left-sided hemiparesis.

For approximately 36 hours prior to contacting 9-1-1 the patient experienced increasing shortness of breath made worse by lying flat or with physical activity (paroxysmal nocturnal dyspnea and new exertional dyspnea).

The patient is found sitting in a living room chair. He is in no acute distress at the time of evaluation.

Skin is slightly “dusky” but warm and dry.

The patient denies chest discomfort. He admits to some nausea but has not vomited. He denies light-headedness and palpitations.

Past medical history: NIDDM, CABG x 4 years ago, myocardial infarction, left bundle branch block, ICD placement

Medications: Numerous but unavailable at the time of evaluation

Vital signs

RR: 22
Pulse: 96 and irregular
BP: 142/82
SpO2: 92 on RA

The cardiac monitor is attached.

A 12-lead ECG is captured.

Here is the computerized interpretive statement.

What do you think is going on with this patient?

Are you concerned about his 12-lead ECG?

You are 15 minutes from the local non-PCI hospital and the STEMI Receiving Center is 45 minutes in the opposite direction.

See also:

63 year old male CC: Chest pain

Posted by on January 28, 2011 • 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 male CC: Chest pain

20 comments

Here’s an interesting case sent in by a faithful reader who wishes to remain anonymous.

EMS is called to the residence of a 58 year old male complaining of chest discomfort.

On arrival the patient is found sitting on the edge of the bed. He is anxious but alert and oriented to person, place, time, and event.

He was awakened from sleep by chest discomfort.

Onset: 30 minutes ago while sleeping
Provoke: Nothing makes the pain feel better or worse
Quality: Severe pressure or “ache”
Radiate: The pain does not radiate
Severity: 10/10
Time: He has had chest pain before but “not this bad”

Past medical history: HTN, dyslipidemia

Medications: Lipitor, Norvasc, ASA

Vital signs are assessed.

RR: 24
Pulse: 136
NIBP: 160/98
SpO2: 94 on RA

Breath sounds: basilar rales

The patient admits to mild dyspnea. He states that he has “gained a little weight” recently and his doctor was getting ready to put him “on a water pill.”

Temp: 99.1
BGL: 138

The cardiac monitor is attached.

A 12-lead ECG is captured.

The patient is given 324 mg of aspirin, 0.4 mg NTG SL spray and placed on CPAP.

Another 12-lead ECG is captured.

The patient is loaded for transport and another rhythm strip is captured.

What do think is going on with this patient’s heart rhythm?

What do you think is wrong with this patient?

You are 15 minutes away from the local non-PCI hospital and 60 minutes away from a STEMI receiving center.

Where would you transport this patient and why?

*** UPDATE ***

This 12-lead ECG was captured en route to the hospital.

And finally this rhythm strip.

Does this shed any light on the mechanism behind the wide complexes?

Posted by on November 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: , , , , , , , , , , , , , , , , , , ,

79 year old male CC: Shortness of breath

19 comments

Here’s another interesting case submitted by Geoff Dayne.

79 y/o male c/o non-provoked SOB without CP.

Patient was found sitting upright, tripodding, 1 word dyspnea.

Lung sounds: extremely decreased tidal volume. EMS crew was unable to tell if there was rales or wheezing.

Past medical history: HTN, dyslipidemia, CHF, pacemaker (recently implanted within a week or so), diabetes, emphysema.

Drug allergies: Sulfa

Current meds: Glipizide, Omerprazole, Hydralizine, Lovastatin, Lasix, Albuterol

Vital signs:

B/P: 154/84
Pulse: 134 Strong/Irregular
Resp: 30
SpO2: 84 on RA

They treated w/ O2 and put him on the patient’s home BiPAP and transported.

A 12-lead ECG was captured.



And a rhythm strip.



I think this case is an excellent example of the real-life difficulties paramedics face in the field when it comes to the triage of possible ACS patients.

What would you do next as the treating paramedic?

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)

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 July 11, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , ,

Discordant ST-Segment Elevation in LBBB or Paced Rhythm

10 comments

If you’ve been following the Prehospital 12-Lead ECG blog for a while, you know that I’m advocate of using Sgarbossa’s criteria to help identify acute STEMI in the presence of left bundle branch block (LBBB) or paced rhythm.

According the Sgarbossa’s original criteria, 5 mm of discordant ST-segment elevation is required to identify AMI in the presence of LBBB.

Why 5 mm when normally we require only 1 or 2 mm of ST-elevation?

Because in the setting of left bundle branch block or paced rhythm, it’s normal for the ST-segment and T-wave to be defected opposite the main deflection of the QRS complex!

That’s why it’s necessary to consider the depth of the QRS complex when examining the amount of discordant ST-segment elevation. The deeper the S-wave, the greater the secondary ST-T wave abnormality in the opposite direction!

In the original article I wrote on the topic, I showed this example 12-lead ECG to show why the 5 mm criterion is problematic.



As you can see, this 12-lead ECG shows sinus rhythm with left bundle branch block and > 5 mm of discordant (opposite the QRS complex) ST-elevation in leads V1, V2, and V3 (the right precordial leads). The T-wave are huge!

The problem is, this patient was not experiencing acute myocardial infarction. The ST-segments are elevated > 5 mm because the S-waves are extremely deep (off the bottom of the ECG paper for leads V2 and V3).

Had we used the modified criterion of discordant ST-elevation that is = or > to 0.2 the QRS complex (ST/QRS ratio) we would have seen that in lead V1 the S-wave is 50 mm deep. Thus, we would require at least 12.5 mm of ST-segment elevation to consider this finding positive for acute STEMI.

(Credit to Dr. Smith’s ECG Blog)

There’s another way the modified criterion can help you!

Consider this 12-lead ECG that shows a ventricular paced rhythm. It’s been in my collection for many years, and I regret that I no longer recall where it came from.



This ECG does not meet Sgarbossa’s criteria for diagnosing AMI in the presence of LBBB. With the exception of lead V6, the paced QRS complexes show appropriate T-wave discordance, and none of the ST-segments are elevated to 5 mm or more.

But wait! The ST-segments are elevated far greater than 0.25 the depth of the QRS complex in leads II, III, and aVF! This patient is experiencing acute inferior STEMI!

The intrinsic QRS complex in the right precordial leads also shows an > R/S ratio in lead V1 and V2 and ST-segment depression suggesting posterior extension, which clinches the diagnosis.

So remember, when using Sgarbossa’s criteria, huge QRS complexes can cause false positive and tiny QRS complexes can cause false negatives, unless you use the modified rule that considers ST-segment elevation as a percentage of the QRS complex!

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

“New” LBBB – What’s the big deal?

Sgarbossa’s Criteria – New Graphic

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)

STEMI best seen in PVC (Dr. Smith’s ECG Blog)

Posted by on January 27, 2010 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , ,

“New” LBBB – What’s the big deal?

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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

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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: , , , , , , , , , , , , , , , , , ,

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

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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: , , , , , , , , , , , , , , , , , , , , , , , ,

The Only Constant Is Change

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In this excellent article from the March 2007 Journal of the Emergency Medical Services, Tim Phalen discusses the importance of performing serial 12 lead ECGs.

Here are some of the highlights.

“Acute myocardial infarctions (AMIs) aren’t like broken bones and, therefore, ECGs aren’t static like X-rays. If an EMS crew were treating a hip fracture and could somehow perform the X-ray on scene, what would it show? A broken hip, of course. And if the X-ray wasn’t performed until the patient arrived at the emergency department (ED), would the broken hip still be visible?

Absolutely.

When dealing with a fracture, whether the X-ray is obtained immediately, in 10 minutes or in 10 hours, the interpretation and diagnosis usually won’t change. But what’s true for X-rays isn’t necessarily true for ECGs. In fact, an ECG can significantly change in a very sort period of time — as can the corresponding interpretation.”

“[I]t can be difficult to determine if the presence of LBBB on the ECG of a suspected AMI patient is preexisting or is a new onset. If the LBBB is infarct-induced, it has a high mortality rate — up to 60%. Therefore, the patients who may need reperfusion the most are the least likely to receive it. However, dynamic changes on serial ECGs shed light on the situation. A hallmark of infarct is change over time. If a patient has had an LBBB for the past 15 years, it’s not likely to change much during the next 15 minutes. But when changes occur in a short period of time, suspect AMI.”

Those are some excellent points.

It’s also helpful to understand the expected appearance of baseline abnormalities. For example, the rule of “appropriate T-wave discordance” states that with bundle branch blocks and paced rhythms, the T-wave should be deflected opposite the terminal deflection of the QRS complex. So LBBB is an abnormal finding, but discordant T-waves (and ST-segments) within the context of LBBB are a normal finding (to a point).

On the other hand, while baseline abnormalities like LBBB or paced rhythm may cause a discordant shift of the ST-segment and T-wave, the ST-segment should not be moving! A moving ST-segment suggests dynamic changes in supply v. demand characteristics.

In other words, ischemia.

Posted by on October 27, 2008 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , ,

The problem of ST segment elevation

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The criterion seems quite simple.

In the absence of contraindications, reperfusion therapy should be administered to patients with symptom onset within the prior 12 hours and ST elevation greater than 0.1 mV (1 mm) in at least 2 contiguous precordial leads or at least 2 adjacent limb leads, or new or presumably new LBBB on the presenting ECG.

However, as I noted in the electrocardiogram section of the myocardial infarction article in the English Wikipedia (I used to edit the Wikipedia quite often, but I probably won’t anymore since I have a blog):

This criterion is problematic [...] acute myocardial infarction is not the most common cause of ST segment elevation in chest pain patients. Over 90% of healthy men have at least 1 mm (0.1 mV) of ST segment elevation in at least one precordial lead. The clinician must therefore be well versed in recognizing the so-called ECG mimics of acute myocardial infarction, which include left ventricular hypertrophy, left bundle branch block, paced rhythm, early repolarization, pericarditis, hyperkalemia, and ventricular aneurysm.

Brady et al. said it best in Electrocardiographic ST-segment elevation: correct identification of acute myocardial infarction (AMI) and non-AMI syndromes by emergency physicians (Acad Emerg Med 2001; 8(4):349-360):

“ST segment elevation is perhaps the “most demanding” of the electrocardiographic features seen in the chest pain patient; it is “demanding” in that its presence must be explained and, if the etiology involves AMI, urgent therapeutic decisions must be made. Unfortunately, STE is a not uncommon finding on the ECG of the chest pain patient; its cause infrequently involves AMI.”

Think about that. Its cause infrequently involves AMI.

How infrequently? In Cause of ST segment abnormality in ED chest pain patients (Am J Emerg Med 2001 Jan;19(1):25-8) Brady et al. performed a retrospective ECG review of adult chest pain patients in a university hospital emergency department (ED) over a 3-month period.

ST segment elevation was determined if the ST segment was elevated >1 mm in the limb leads or >2 mm in the precordial leads (in at least two anatomically contiguous leads).

902 patients were enrolled in the study. Of those, 202 patients (22.4%) had ST segment elevation on their initial 12 lead ECG. Of those, only 31 patients (15%) had a discharge diagnosis of STEMI. In other words, 171 patients (85%) had a non-AMI cause of ST segment elevation on their initial 12 lead ECG.

So what were the other causes of ST segment elevation?

Left ventricular hypertrophy (LVH) – 51 cases (25%)
Left bundle branch block (LBBB) – 31 cases (15%)
Benign early repolarization (BER) – 25 cases (12%)
Right bundle branch block (RBBB) – 10 cases (5%)
Nonspecific BBB – 10 cases (5%)
Ventricular Aneurysm – 5 cases (3%)
Pericarditis – 2 cases (1%)
Undefined or unknown cause – 35 cases (17%)

44 patients had AMI as the final diagnosis of whom 31 showed ST segment elevation on presentation to the ED. In 2 of 31 (6%) cases of STEMI, the ST segment waveform was atypical for acute infarction.

Their conclusion:

“AMI is not the most common cause of ST elevation in ED chest pain patients. LVH is most often responsible for electrocardiographic STE followed by AMI and LBBB which occur at equal frequencies.”

As a side note, I find it a bit unusual that paced rhythms are not mentioned (unless they fell into the nonspecific BBB category for some reason). It also seems strange that RBBB is listed as a cause of ST segment elevation. In my experience RBBB does not distort the ST segment the way LBBB does. That’s not to say that it’s always easy to identify STEMI in the setting of RBBB, just like it’s not always easy to identify STEMI in the absence of bundle branch block.

*** Update 12/20/08: I recently saw an ECG with sinus tachycardia and RBBB that appeared to show ST segment elevation. The patient was emergently cathed and no culprit artery was found. The absence of a well defined TP segment as a baseline for comparison was a confounding factor. ***

Regardless, the message is clear. It’s not enough to discover ST segment elevation on the 12 lead ECG of a chest pain patient. A monkey could do that. We need to specifically discover the ST elevation of AMI.

Consider Sejersten et al. Comparison of the Ability of Paramedics With That of Cardiologists in Diagnosing ST-Segment Elevation Acute Myocardial Infarction in Patients With Acute Chest Pain (Am J Cardiol 2002 Nov 1;90(9):995-8):

“Paramedics diagnosed over half of patients as having ST elevation AMI, when in fact they did not. One reason for this may be that the paramedics were concerned about missing patients with this condition. The number of false-positive diagnoses may also have been increased due to the problem of differentiating ST elevation AMI from other electrocardiographic abnormalities that result in ST-segment elevation…”

“The paramedics’ diagnosis of ST elevation AMI was confirmed in 55 patients (45.5%) by acute angiography. In an additional 4 patients (3.5%) who did not undergo angiography due to high-risk assessment or other causes, the diagnosis was confirmed clinically by typical electrocardiographic changes in evolving ST elevation AMI accompanied by transient elevation of creatine kinase-MB. Thus, the paramedics’ true positive rate was 49% (n = 59). The paramedics’ decision was not confirmed in the 23 patients (19%) with no thrombus at angiography, and in the 38 (31%) who did not undergo coronary angiography because the attending cardiologist judged them not to have an evolving ST elevation AMI [...] The false-positive rate by paramedics was 51% (n = 62)…”

The authors also observe:

“The incidence of poor quality ECGs recorded by the paramedics was calculated to determine the paramedics’ performance in electrocardiographic acquisition. In 13 of 124 patients (10.5%), the ECGs were characterized as poor quality…“

Amazingly, they refer to this as “acceptable.” I guess their standards are low! They’re either satisfied with the care of 1 in 10 patients being compromised by poor data quality, or they think that’s all EMS is capable of.

Their conclusion?

“This study concludes that paramedics’ true-positive rate of ST elevation AMI diagnosis is high in patients presenting without confounding factors, but decreases when the ECG has confounding factors. This is in contrast to an experienced cardiologist whose true-positive rate was high and not affected by confounding factors. The results demonstrate that before implementation of electrocardiographic transmission directly to a cardiologist’s handheld device, there is a need to provide education and training to paramedics responsible for acquiring and interpreting prehospital ECGs, with special emphasis on confounders…“

To all the paramedics out there who feel offended that they’re being asked to transmit the 12 lead ECG to the emergency department for physician interpretation, do you know how to identify all of the mimics of acute myocardial infarction? Do you know how to identify acute myocardial infarction in the presence of baseline abnormalities?

We’ve been taught that identifying acute STEMI on the 12-lead ECG is easy! And so it is… to a point. Identifying ST segment elevation that is not STEMI… that’s the trick.

It’s false positives that cause the most problems!

Here’s a final thought from Otto and Aufderheide, Evaluation of ST segment elevation criteria for the prehospital electrocardiographic diagnosis fo acute myocardial infarction (Ann Emerg Med 1994 Jan;23(1):17-24):

“Fifty-one percent of patients whose prehospital 12-lead ECG met 1 mm or more ST segment elevation criteria had non-myocardial infarction diagnoses. ST segment elevation alone lacks the positive predictive value necessary for reliable prehospital myocardial infarction diagnosis. Inclusion of reciprocal changes in prehospital ECG myocardial infarction criteria improved the positive predictive value to more than 90% and included a significant majority (62% to 86%) of acute myocardial infarction patients with ST segment elevation who received thrombolytic therapy within five hours after hospital arrival. ST segment elevation criteria that include reciprocal changes identify patients who stand to benefit most from early interventional strategies.“

Thanks to ncline7 for reminding me that you can test your ability to identify the mimics of acute STEMI by taking the ACC-D2B ECG Challenge!

Posted by on October 26, 2008 • Filed under: ems-topics, patient-management • Tagged: , , , , , , , , , , , , , , , , , , , , , ,