Thursday, February 15, 2018

A female in her 60s who was lucky to get expert ECG interpretation

Submitted and written by Alex Bracey, with edits by Pendell Meyers and Steve Smith:

I was walking through the critical care section of the ED when I overheard a discussion about the following ECG. I had no history on the case and no prior ECG for comparison.

What do you think?




Here are inferior leads, and aVL, magnified:
A closer inspection of the inferior leads and aVL
Sinus bradycardia. 
The T-wave in lead III is slightly tall and broad (increased area under the curve) compared to its QRS complex. In isolation, this probably could not be called a hyperacute T-wave, but you may suspect it.   
There is T-wave inversion (TWI) in aVL.  

T-wave inversion in aVL: when is it abnormal?

There is no LVH or LBBB on which to blame the TWI (i.e., the QRS is normal). While T-wave inversion in aVL may be normal in the presence of a normal QRS, this is only true when the T-QRS angle is small. That is to say, when the T-axis and QRS axis are similar. In other words, if the QRS is negative, the T-wave may be negative. However, here QRS axis is about 35 degrees and the T-axis is about 85 degrees. Thus the T-QRS angle is 25 - 85 = (-60) degrees, which is abnormal. Any absolote value greater than 45 degrees is suspicious for T-wave inversion (however, this is very complex; see table posted at the bottom of this post.)

Now that we know the T-wave inversion in lead aVL following a normal QRS complex is abnormal, it helps to confirm that the T-wave in lead III is indeed hyperacute. The flattened T-wave in V2 suggests likely posterior involvement.

The cath lab was not activated based on this initial ECG. The patient was a female in her 60s with history of HTN and smoking who presented for chest pressure x1 hour. The initial ECG was taken at 0839. Based on the initial ECG and presenting complaint, the attending involved in the case opted to keep the patient in our critical care unit for close monitoring and serial ECGs.


She went on to describe her chest pain as a "buffalo sitting on my chest" and a "weird" sensation in her jaw for 1 hour prior to arrival, associated with lightheadedness and diaphoresis.


The patient was given fentanyl initially for chest pain with minimal effect and then vomited which was followed by zofran and famotidine. Initial troponin T from 0840 was less than 0.010 ng/mL (undetectable).


The following ECG was obtained at 0910:


Repeat ECG recorded 30 minutes after initial ECG. The patient still had chest pain.
Magnified:
Again, a close up of the interior leads and aVL





Sinus rhythm with borderline 1st degree AV block. There has been interval marked increase in the area under the ST-segment and T-wave in leads II, III, and aVF, with concomitant increase in the area above the inverted T-wave in aVL, all confirming that that these truly represent inferior hyperacute T-waves. The STE in the inferior leads is larger. There is now TWI and small STD in lead V2, highly suspicious for posterior MI. 


This ECG is diagnostic of an acute coronary occlusion of an artery supplying the inferior and posterior walls.


The cath lab was activated following this ECG and the cardiology fellow came to the bedside. The patient was given aspirin and ticagrelor and was scheduled for urgent cath.


In the cardiac cath holding area, a repeat troponin T was 0.01 ng/mL (positive). The following ECG as recorded at 1206:


Pre-cath right sided ECG. V1 and V2 are unchanged from the normal 12-lead sytem; V3-V6 are actually V3R-V6R.
The T-waves are even more hyperacute. Right sided leads (V3-V6 on this ECG correspond to V3R-V6R) have STE and hyperacute T-waves indicative of RV infarction.

Progression of Inferior leads and aVL

In this magnified arrangement you can see progression of subtle changes including the progressively increasing area underneath the hyperacute T-waves. Even at ~4 hours into her acute coronary occlusion there is barely any ST Elevation. 

Also notice that the ST segments in this example are concave, which is often erroneously mythologized as a non-ischemic pattern.  



Progression of V2 showing posterior involvement.



The patient was then taken to the cath lab an found to have a proximal RCA 100% thrombotic occlusion which was successfully stented.


100% occluded RCA with TIMI 0 flow

Post drug-eluting stent placement with TIMI 3 flow


While in the cath lab, she transiently developed complete heart block and became hypotensive requiring transvenous pacemaker placement and transient pressors. A right heart cath revealed increased right heart pressures and a similarly timed echo revealed mild right heart failure.

Peak troponin T was 3.00 ng/mL (highly elevated).

Post-cath ECG with resolution of acute changes.


The transvenous pacemaker was removed the following day and pressors were not required again. She was discharged to home 2 days later without further complications.

Learning Points:

1) As we have previously demonstrated, aVL was once again the key initial clue to diagnosing subtle RCA occlusion.

2) Contemporary troponins only start to rise 4-6 hours after the onset of acute coronary occlusion. Relying on troponin elevation to diagnose acute coronary occlusion after at least 4 hours of infarction when the ECG can identify it immediately is poor choice.

3) STEMI criteria failed to identify this acute coronary occlusion, like many others. Only expert ECG interpretation combined with strong clinical suspicion were able to identify this case. Remember that some acute coronary occlusions will present with totally normal serial ECGs, and some patients with extremely concerning symptoms warrant emergent cath lab activation even without ECG findings.


Normal QRS-T angle

From this article: Ziegler R and Bloomfield DK.  A study of the normal QRS-T angle in the frontal plane.  Journal of Electrocardiology 3(2):161-167; 1970.  

Yes, there are valuable articles from 50 years ago! 

For each QRS angle on the left column, Ziegler and Bloomfield have found the normal range of T angles. You can see that, for a QRS angle of 25, as in our patient, the normal range of T angles would be 2-69. So our patient really does have an abnormal T axis at 85 degrees, and the "inverted," or negative, T-wave really is abnormal inversion. A negative T-wave in aVL must have an angle of greater than 60 degrees.


Sunday, February 11, 2018

Is there Wellens' syndrome in left bundle branch block? Or in inferior and lateral leads?

Written by Pendell Meyers, with edits by Steve Smith


A male in his 80s old had acute onset of chest pain.  Here is his first ECG, time zero:
What do you think?









Sinus rhythm with left bundle branch block. There is concordant STE in leads II, V5, and V6. It may not reach a full millimeter, but the QRS is so small that we should make an exception here. It is proportionally large concordant ST elevation!


The cath lab should be activated, but apparently it was not.  Instead, another ECG was recorded at time 46 minutes:
Now there is more than 1 mm of concordant ST elevation in leads II, V5, and V6.
In addition, there is now excessively proportionally discordant (more than 25% of preceding S-wave) in leads III, and aVF.
So there is a definite inferior and lateral MI.  There is no ST depression in lead I, which suggests a circumflex lesion as the culprit.

The cath lab was activated and a circumflex occlusion was opened and stented, with a door to balloon time of 3 hours.


Here are ECGs recorded after reperfusion:
ST deviation has resolved. There is already terminal T-wave inversion in leads III and aVF.




T-waves are inverting in the affected leads.
This is analogous "Wellens' waves" of the inferior and lateral leads, in the presence of LBBB!


As an explorative substudy of our validation of the modified Sgarbossa criteria, we studied T-wave inversion. We looked at serial ECGs on patients with acute coronary occlusion ACO) who underwent reperfusion and compared to serial ECG on patients without ACO. Unfortunately, as a result of our multisite study in which ACO came from many institutions and controls from one institution, only 6 of 45 patients with ACO and reperfusion had serial ECGs available, and all 245 patients without ACO had serial ECGs available.

When this pattern was retrospectively defined as being either 1) present in at least two
contiguous anterior or inferior leads in at least two consecutive ECGs prior to reversal or 2) deeper than 3 mm in two contiguous leads (requiring only one ECG), it was found to be predictive of reperfused ACO (either spontaneously prior to catheterization or with mechanical reperfusion) with derived sensitivity and specificity of 5 of 6 [83% (95% CI 36–99%)] and 241 of 245 [98% (95% CI 96–99%)]. This is preliminary low-level evidence which suggests that terminal T-wave inversion as a sign of reperfusion is sometimes still applicable in the setting of abnormal QRS such as LBBB and likely ventricular paced rhythm as well.


Meyers HP.  Jaffa E.  Smith SW.  Drake W. Limkakeng AT.  Evaluation of T-Wave Morphology in Patients With Left Bundle Branch Block and Suspected Acute Coronary Syndrome.  Journal of Emergency Medicine 51(3):229-237; September 2016.


We (Meyers and Smith) also published a case of Wellens' syndrome (involving the LAD) in LBBB:

Dynamic T-wave inversions in the setting of left bundle branch block


As a very brief review for new readers, terminal T-wave inversion is an expected finding with reperfusion of acute coronary occlusion which is well established in the presence of normal QRS conduction (no LBBB, paced rhythm, etc). It was first described by Wellens and colleagues in the anterior leads in the setting of an acute proximal LAD stenosis, and later it was more fully understood as a transient phase of reperfusion soon after acute coronary occlusion. When it was first described, it was initially divided into "pattern A" and "pattern B", characterized by biphasic terminal T-wave inversions then full, symmetric T-wave inversions, respectively. In reality these are not separate presentations of the disease but simply two different time periods during the progression (see progression below).

Furthermore, though Wellens described this pattern only in LAD leads, it is clear that it occurs in inferior and lateral leads as well.
See this case of inferolateral Wellens' syndrome, with subsequent re-occlusion and pseudonormalization of T-waves.






See this post: Classic Evolution of Wellens' T-waves over 26 hours

See these posts for Pseudonormalization of Wellens' waves (re-occlusion):

This one is EXTREMELY subtle: 

A Middle-Age Male with Chest Pain that Recurs in the ED


Pseudonormalization of Wellens' Waves


Subtle LAD Occlusion with Pseudonormalization of Wellens' Waves.


This one shows why patients with Wellens' syndrome who do not go immediately to the cath lab need continuous 12-lead ST Segment monitoring:



Thursday, February 8, 2018

New paper by Smith: New Insights Into Use of the 12-Lead ECG for Diagnosing Acute MI in the Emergency Department


We just published this paper in the Canadian Journal of Cardiology.  The February 2018 issue is on "Advances and Controversies in Cardiac Emergency Care:"

New Insights Into the Use of the 12-Lead Electrocardiogram for Diagnosing Acute Myocardial Infarction in the Emergency Department


It is a very comprehensive update, concentrating on the ECG diagnosis of acute coronary occlusion and its look-alikes.

Unfortunately, it will be difficult for many to get full text.

https://www.sciencedirect.com/science/article/pii/S0828282X1731173X


Syncope and Prehospital Cath Lab Activation for Posterior STEMI

A middle-aged man had syncope.

This ECG was recorded prehospital; here are the limb leads:
What do you think?







Notice that there are inverted P-waves and a very short PR interval.  This is a junctional rhythm with retrograde P-waves that come slightly before the QRS.  Otherwise, it is unremarkable. 


Here are the Precordial leads:
What do you think?





Here is what the computer read:
Why did it read this?






The computer sees ST depression in V3 and V4, which normally is indeed nearly diagnostic of posterior STEMI.

Is it posterior STEMI?

The computer measures ST elevation or depression at the J-point, relative to the PQ junction.  There is indeed quite a bit of ST depression relative to the PQ junction, but the PQ junction is artificially elevated as an artifact of the P-wave, which is fused with the QRS:

The black arrow shows the PQ junction.  Note that the P-wave occurs just prior to the QRS and is fused with the QRS.  This artificially elevates the PQ junction.  The red arrow shows where the PQ junction really should be.  The blue arrow shows the J-point.
So there really is zero ST depression.



We saw this and de-activated the cath lab immediately.

Learning points:

1. When the patient does not have chest pain, scrutinize the ECG even more closely.  There should always be some suspicion for a false positive when syncope only is the presenting complaint.

2. Read the entire 12-lead ECG.  Our eyes always want to look for ischemia by looking at ST segments and T-waves.  But abnormalities, or apparent abnormalities, of repolarization may be entirely a result of abnormal rhythm or abnormal QRS.




Wednesday, February 7, 2018

ST Elevation after Stab Wound to the Heart

A young man presented after a stab wound to the chest.  Rapid ED diagnosis of cardiac penetrating trauma was made by ED ultrasound, and the patient went to the OR and had a wound to the right atrium repaired.  There was no laceration of any coronary vessel.  He did well.  Because of tachycardia, this ECG was recorded at day 3:

There is sinus tach with diffuse ST elevation, and a bit of ST depression in lead III.  There is PR depression, especially in leads II and V5.  QTc is 383 ms.
This diffuse ST elevation is clearly due to pericarditis, especially given the clinical scenario.  It is slightly unusual, though: The ST vector is directly lateral (highest STE in lead I, with some reciprocal ST depression in lead III).  

[It is unusual to have any ST depression in percarditis, and, if the scenario is one of possible ACS, it would not be wise to assume that diffuse ST elevation is pericarditis without first considering high lateral MI.]

Other ECG factors also support pericarditis: short QTc, significant PR depression, and especially the high ST elevation to T-wave amplitude ratio (in other words, the T-waves are relatively flat, thus non-ischemic).  There is no Spodick's sign (downsloping TP segment).

2 weeks later, his ECG had evolved:
There is resolution of ST elevation, except in V1-V3, and there is now T-wave inversion in V1-V3.

This looks a lot like a common normal variant, and it may actually be, even if it is not seen on the 4 month ECG below.

4 months after the stab wound, it was all resolved:


2 months later (6 months after the stab wound), he again presented with pain typical of pericarditis:
This is more typical: inferolateral ST elevation (ST vector towards lead II), with no reciprocal ST depression.  PR depression is again present.

He was treated with colchicine and NSAIDs, and discharged.

Monday, February 5, 2018

Chest pain and a non-diagnostic ECG. No worries, right?

A middle-aged male complained of chest pain and called 911.  3 prehospital ECGs were recorded.


Here is the time zero ECG:
Just some non-diagnostic T-wave abnormalities  
T-wave inversion in V2 is a bit abnormal, and frequently seen in posterior MI, but not diagnostic. 
 There is tiny bit of ST depression in V3 and V4 which is nonspecific and could be normal.  
There is a large T-wave in lead II which is also nonspecific.  

Here is the repeat at t = 9 minutes:
Lots of artifact, but no apparent change


Here is the t = 25 minute ECG:
Again, no significant change except that the ST segments in V3 and V4, which previously showed some minimal ST depression, are no longer depressed.











The patient arrived in the ED and, before another ECG could be recorded, he had a V Fib arrest.

He was defibrillated, then taken to the cath lab and had a 100% circumflex occlusion.

He did well.

MI in the setting of a normal or nondiagnostic ECG:

This is very common.  Approximately 30% of MI have no diagnostic STE, STD, or T-wave inversion; in other words, they have no ECG findings specific for ischemia.  It is also true that  approximately 25-30% of complete occlusions do not have diagnostic ST elevation (but most have some evidence of ischemia!).

This is the reason we do not rely on the ECG to rule out MI!   Over the years, I have shown you many ECGs that show evidence of MI that might not be seen by everyone, or evidence of coronary occlusion that might not be seen by everyone.

This one has no clear evidence of occlusion, and no reliable evidence of MI at all (occlusive or non-occlusive).

Learning Point: patients can have MI with a normal or nondiagnostic ECG, and they can even have complete occlusion!

That said, I showed it to Vince DiGiulio and he wrote back:

Going into this I figured the ECG showed ischemia since you shared it, but I'm being honest that I didn't look at the outcome when I formulated my opinion (I sound like Ken). My thoughts were:
  • My pretest probability of ischemia is high since Steve Smith sent this. I consider it similar to the patient coming in with a good story and positive Levine sign.
  • There is slight ST-depression in V3 relative to the PR, but absolutely no ST-depression in V6. In my experience, when there is a decent pretest probability, that correlates highly with isolated posterior MI and is almost always due to LCx culprit. If the patient came in with belly pain I wouldn't pay it might mind, but typical CP and this ECG has me thinking LCx until proven otherwise.
I wasn't at all surprised to hear it was a 100% LCx.

The circumflex territory is the most "electrocardiographically silent" of the three epicardial arteries.  50% of circ occlusions do not show diagnostic ST elevation, but most do show some ST elevation less than 1 mm, or some ST depression.

Many circ occlusions result in only ST depression in leads V1-V4 [formerly known as isolated "posterior MI", but now the echo and MRI societies want to call them all lateral or inferior -- (a mistake if you ask me, but more on that later)].  If you do suspect occlusion but see no ST depression or elevation, try posterior leads V7-V9.  Remember that the voltage of the QRS and of the ST segment and T-wave are diminished by the impedance of the lungs between the posterior wall and the posterior leads.  Thus, data supports a cutoff of 0.5 mm of ST elevation (not 1 mm) when there is posterior ischemia.  Like all other distributions, millimeter cutoffs have very imperfect sensitivity and specificity, and do not capture the changes of ACO that can be seen by a skilled interpreter.

Also, posterior leads are not sensitive enough to rule out posterior MI; frequently patients with right precordial ST depression from acute posterior MI do NOT have any posterior ST elevation.  So if you make the diagnosis on the 12-lead, do not reverse your diagnosis based on absence of STE in posterior leads.

In any patient, if you strongly suspect ACS and the patient has continued, refractory pain, the European Society of Cardiology AND the ACC and AHA all recommend urgent (less than 2 hours) angiogram.  However, this makes it very easy to have false positives, as we know that many patients have ongoing noncardiac chest pain.  So this requires great clinical skills (or luck)!   A positive troponin, or stat echocardiogram, or continued serial ECGs (or a cardiac arrest!) may help to identify these patients.

It should be rare that you activate the lab in the absence of all of these!

Thursday, February 1, 2018

This ECG was shown to the doctor with no clinical information

Written by Pendell Meyers, with edits from Steve Smith



I was charting at my computer on a busy overnight shift when a triage ECG was placed between my face and computer screen, asking for my signature. Here it is:
What do you think?











--Sinus rhythm.
--There is a tiny amount of STE in the inferior leads, with lead III having possibly a large T-wave compared to its QRS complex.
--Lead aVL clinches the diagnosis with a very small normal QRS complex followed by minimal ST depression and a proportionally massively inverted T-wave.
--Lead I also shows reciprocal STD.
There is obvious STD in V2-V4 which indicates posterior involvement.
This ECG is diagnostic of acute coronary occlusion affecting the inferior and posterior walls.


Let's look at the magnified limb leads:
Now the findings are more clear


And the magnified precordial leads:
Note clear ST depression in V2, subtle in V3

Subtle ST depression in V4


I asked the triage nurse to bring him back into a room in my zone immediately, and to perform serial 15 minute ECGs as well as labs and cardiac monitor. Although these changes are clear to me, I knew this would be somewhat difficult to convince the cardiologists and I may have to get serial ECGs until more obvious findings are present.

I went to assess the patient. I found out the ECG belonged to a male in his 40s with hypertension who presented with chest pain that woke him from sleep. He stated he had similar chest pain last night which subsided, and he was able to go to sleep only to be awoken several hours later by recurrent pain.

Here is his previous ECG on file:
This further confirms that the findings in the presentation ECG are real and acute.


At this point I got a repeat ECG (approximately 20 minutes after arrival):
This shows increased STE in the inferior leads, increased STD in aVL, increased STD in V2-V4. All indicative of progression of acute coronary occlusion.

I activated the cath lab.

He was taken for emergent cath:
Patent RCA.

This is the so-called "spider view," in which you can see the clean bifurcation of the left main coronary artery into the LAD and the LCX. Soon after the LCX splits off, it quickly branches into two vessels. The larger caliber vessel shows complete proximal occlusion with TIMI-0 flow.  
This was diagnosed as a 100% thrombotic occlusion of the (very large) proximal segment of OM1.  PCI was performed and was able to reduce the stenosis to 50%.

The first troponin T returned highly elevated at 1.33 ng/mL. No more troponins were available.

This is a surprisingly high Troponin T.  It suggests that the patitent's infarct has been going on longer than one would have thought, or that the pain the patient had experienced earlier in the night had resulted in significant myocardial infarct (permanent injury).

Here is his ECG after cath:
ST segment and T-wave findings have almost all resolved.
There are new Q-waves, with T-wave inversion, in lead III.
The T-wave in aVL is now upright.

Learning Points:

1. Lead aVL once again holds the key to the interpretation of subtle findings in the inferior leads.

2. If you weren't convinced by limb leads (although you should be), ST depression in precordial leads make this even more certain -- they complete a pattern of coronary distribution.  Any artery that supplies the inferior wall (could be either RCA or Circumflex) also often supplies the posterior wall.

3. Serial ECGs are always helpful.

4. Acute coronary occlusion frequently does not manifest the classic STEMI criteria.








Tuesday, January 30, 2018

Bizarre (Hyperacute??) T-waves

Thanks to one our great HCMC nurses, Ryan Burch.  He figured this one out.

A dialysis patient presented with dyspnea.  He was a bit fluid overloaded and not hyperkalemic.

 This ECG was recorded:
This was sent to me in a text that woke me from sleep, but not simultaneous with patient care.
Truly bizarre T-waves in I, aVL, III, aVF, aVR
Lead II is unremarkable, and leads V3-V6 are also slightly bizarre.

What do you think?
















My answer, as I looked with bleary eyes at my phone: "I have to say I've never seen this one before."

Later, I looked into the chart and found an ECG from a few days before:
I texted back:
"Those T-waves were gone 5 minutes later.  Artifact!"






Ryan Burch, RN, was the nurse caring for the patient, later sent me the same ECG, stating the following:

"This ECG had people stumped and concerned but I read an article in www.ecgmedicaltraining.com (see below) about an artifact a few weeks prior which I thought looked similar and the suggestion was that a lead had been placed over an artery.  I switched lead placement and this ECG was recorded 5 minutes later:"

He found that the left arm electrode had been placed near the patient's left arm dialysis fistula, which was pulsating with a palpable thrill.

This resulted in the following:
Wandering Artifact only



Explanation

All leads are derived from 3 bipolar electrodes and one unipolar electrode.
Leads I, II, and III depend on bipolar leads voltage differences:
--Lead I uses the right and left arm
--Lead II uses the right arm and the leg
--Lead III uses the left arm and the leg.
--The Wilson (or Goldberger) Central Terminal is used to produce the augmented (a) leads:
aVR, aVL, aVF.
  • The voltages are calculated as follows (thanks to Ken Grauer for sending these):
  • I = L - R
  • II = F - R
  • III = F - L
  • aVR = R - (L + F/2)
  • aVL = L - (R + F/2)
  • aVF = F - (R + L/2)
As you can see, the only lead that does not use the left arm electrode is lead II.  Since lead II is the only normal lead in this ECG, the left arm electrode must be the affected electrode.  Indeed, the patients dialysis fistula was on the left arm and was pulsating with each heart beat, moving the electrode and causing artifact.

Arterial pulse tapping artifact

https://www.aclsmedicaltraining.com/blog/guide-to-understanding-ecg-artifact/

This online article references the article below by Emre Aslanger, a great guy who occasionally corresponds with me about ECGs.

Aslanger E, Yalin K. Electromechanical association: a subtle electrocardiogram artifact. Journal of Electrocardiology. 2012;45(1):15-17. doi:10.1016/j.jelectrocard.2010.12.162.

Incredibly, this case was just published in Circulation on January 22, 2018 (thanks to Brooks Walsh for finding this!) 
Asymptomatic ST-Segment–Elevation ECG in Patient With Kidney Failure.   https://doi.org/10.1161/CIRCULATIONAHA.117.032657.  Circulation. Originally published January 22, 2018

Here is a case from Circulation year 2000 that was misdiagnosed as due to pancreatitis.  But you can tell from the normal lead III that this was a right arm electrode problem:
http://circ.ahajournals.org/content/101/25/2989.full

It is full text!! 

Why is there also artifact in precordial leads?
Aslanger explains:
“[O]ne may expect that the leads not connected to the electrode affected by the source of disturbance would be free of distortion; but this is not the case. When one of the limb electrodes is affected by a source of disturbance, it distorts not only the corresponding derivation but also [the others] which are all calculated by mathematical equations…”
“…precordial leads [are also affected] because the Wilson central terminal, which constitutes the negative pole of the unipolar leads, is produced by connecting 3 limb electrodes via a simple, resistive network to give an average potential across the body.”

Sunday, January 28, 2018

Is this ECG diagnostic of coronary occlusion? Also: Inferior de Winter's T-waves on prehospital ECG??

This post was written by one of our fantastic Hennepin County Medical Center Emergency Medicine interns who is an ECG whiz, Daniel Lee.

A man is his late 50’s presents to the ED with 1 hour of post exertional chest pressure associated with diaphoresis and nausea.  He has a history of known CAD, diabetes, and dyslipidemia.

By pure clinical appearance, he looked like the textbook patient with acute MI.

This is his first ECG in the department, which I saw as it was being printed:
What do you think?

Here is his previous ECG:











This was my interpretation of the first ECG:
Sinus bradycardia with less than 1mm ST elevation in V4-V6, elevated compared to the previous ECG, suggestive of lateral MI.  Looking to the high lateral leads, instead of ST elevation that one might see in a lateral MI there is subtle ST depression in aVL less than 1mm along with new T-wave inversion.  
Leads II, III, aVF show about 0.5 mm ST elevation that is new compared to the previous ECG.  Furthermore there is a new positive T wave in lead III.  
Subtle changes, but with the history is very nearly diagnostic of acute inferior MI. 

Let's look at the 2 ED ECGs side by side:
Limb leads
Now you can see the differences more clearly



Precordial Leads

Acute ECG on the left, with slight STE in left precordial leads, 
compared to the previous ECG on the Right.





This patient had had two prehospital ECGs recorded, and these were viewed:
30 minutes after reported onset of pain:
Sinus rhythm with only a small amount of elevation in V5 and V6.  No ST elevation in the inferior leads, no T wave in III, no ST depression in the lateral leads.
T-waves are small in inferior leads.
This is a negative ECG.


10 minutes after first prehospital ECG, with continued pain:
Smith comment: This shows ST depression in multiple leads, most pronounced in V2-V4.  This is very suggestive of posterior MI.  
There is also some subtle ST depression in II, III, and aVF, and it is followed by T-waves of increased size over the previous.  

Notice how useful serial ECGs are!  


More Smith comment: it is true that ST depression (STD) due to subendocardial ischemia does not localize [it is usually diffuse ST depression, in multiple leads and not reciprocal to ST elevation in an opposite territory], this ST depression is different! The STD in V2-V4 is almost certainly reciprocal STD, reciprocal to STEMI in the posterior wall; this is evident because it is maximal in V2-V4, not in V4-V6.  

So what is the STD in II, III, and aVF?  While de Winter's T-waves have only been described in the LAD territory, there is no reason that they might not also exist in other territories.  Since this is upsloping ST depression followed by an enlarged T-wave, I believe these are Inferior de Winter's T-waves.

There is evidence that de Winter's T-waves really represent a tiny trickle of blood through the thrombotic stenosis.  There is enough limitation of flow to cause subendocardial ischemia with ST depression, and even enough limitation of flow to have hyperacute T-waves, but too little flow to have ST elevation!  I believe this based on much experience of seeing dynamic changes from STE to deWinter's and back again and correlating this with angiograms.

So this is an infero-posterior MI, with affected leads inferior (de Winter's and later STE), posterior (STD V2-V4), and lateral (STE V4-V6).

The interesting thing is that they manifest ischemia at different times:

--When there is clear ST depression of posterior MI in V2-V4, and inferior de Winter's T-waves, there is no ST elevation in V5 and V6.
--When there is STE in V4-V6, and in inferior leads, there is no ST depression in V2-V4.


---------------

The ED ECG in the context of the prehospital ECGs was indeed diagnostic of acute coronary occlusion.

Cath Results:

The cath lab was activated and co-culprit lesions were found: 99% circumflex and 95% right coronary artery (RCA).  Both were stented.

Peak troponin was (0.446 ng/mL) -- very low due to rapid reperfusion.

Subsequent echo showed no wall motion abnormality.

Learning Points

Lead aVL is incredibly useful.  New ST-depression (without LBBB or LVH) in aVL that cannot be blamed on an abnormal QRS is worrisome, and in the context of a patient with acute chest pain is almost certainly due to ischemia.  In patients with suspicion of acute MI who have any ST elevation, aVL is also a very useful lead to differentiate between pericarditis and MI.

This paper by Bischof and Smith compared inferior MI to pericarditis and found that of 154 patients with inferior STEMI, 17% of whom had less than 1 mm of STE in any inferior lead, all 154 had at least 0.25 mm ST depression in aVL.  Among 49 patients with pericarditis who had inferior ST elevation, zero of 49 had ST depression in aVL (though there are always rare exceptions such as this case).  Interestingly this study also looked at 54 “subtle” inferior MI’s, and of these 49 had some ST depression in aVL.  Thus it is not surprising that the current case of subtle inferior MI had ST depression in aVL. Moreover, T-wave inversion in aVL was also found to be 100% sensitive and 86% specific for inferior STEMI.


Here is a magnified in view of aVL side-by-side with the baseline ECG.
Presenting with STD and TWI
Old with no STD









In additions, this paper also found that all 33 patients with inferolateral MI, as manifested by STE in V5 and V6, still had ST depression in aVL.  V5 and V6 are caudal to aVL and so an inferior ST vector towards lead aVF is also slightly towards V5 and V6 but away from aVL!!  So V5 and V6 will have some ST elevation while aVL has ST depression.  Thus, even inferolateral MI has reciprocal ST depression in aVL.   

This patient functionally had an inferolateral MI given his two culprit lesions and in retrospect the elevation in leads V4-V6 were indicative that there was lateral wall involvement as well.  The lateral involvement may also explain the very subtle nature of the acute ECG findings given that much of the voltage in inferior and lateral occlusions are directly opposed to each other. 


This is the post cath ECG:
Resolution of ST depression and T wave inversion in aVL, as well as the new T wave that had been present in III.  There is some residual ST elevation in the inferolateral leads.


Summary of Learning Points:
1. New ST depression and T wave inversion in lead aVL is highly suggestive of inferior MI.
2. Even very subtle inferior MI will likely have ST-depression in aVL.  These ECGs must be scrutinized very closely!
3. Inferolateral MI will have ST depression in aVL in addition to ST elevation in V5 and V6.  
4. de Winter's T-waves may occur in any coronary distribution.

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