Wednesday, July 7, 2021

Chest pain and ST Elevation.

 A 42 year old presented with chest pain.  Here is his triage ECG:

What do you think?

'This is a classic pattern of ST Elevation that everyone should recognize.  

There are QS-waves in V1-V4, with slight ST elevation in V1-V3.  (QS-wave means a Q-wave with no R-wave at all, in contrast to a QR-wave or qR-wave).  This is "Left Ventricular Aneurysm (LVA)" morphology and is due to Old Completed (Transmural) Anterior MI, which often results in an LV aneurysm and manifests on the ECG as "persistent ST elevation after old MI."

The T-wave may be upright or inverted.  See 2 examples below.

In either case,  LVA has a small T-wave (small upright or small inverted -- not tall/wide nor inverted and deep/wide).  

In any case, an inverted T-wave should tell you that the artery is not acutely and persistently occluded, unless it is a completed transmural OMI.  

If the T-wave is upright, then occlusion is possible, but the significance of an upright T-wave depends on its size relative to the QRS: We have developed a formula for differentiating acute anterior OMI from Old or Subacute anterior MI, which I discuss below. 

This patient had a cardiac POCUS in the ED (here is parasternal long axis):

On the far left, see the out-pouching of the apex, especially with every systolic beat. This is a left ventricular aneurysm.

Review of the chart revealed history of large MI, subsequent heart failure, and a previous identical ECG and previous formal contrast echocardiogram.

Previous formal contrast echocardiogram

The estimated left ventricular ejection fraction is 35 %.

Regional wall motion abnormality-distal septum anterior and apex large, dyskinetic.

Regional wall motion abnormality-distal inferior wall akinetic.

"Dyskinesis" is echo-speak for aneurysm.  Not all ECG LVA have actual anatomic LVA, but they all have at least "Akinesis."

Differentiate acute OMI from LVA on echo?  If one has acute OMI and LVA on the ECG differential, can one see a difference between acute OMI and LV aneurysm on echo?    

Acute OMI: there will be akinesis or hypokinesis without wall thinning and without dyskinesis.

LV Aneurysm: there may be akinesis or dyskinesis, and if you are good enough, and have excellent images, you may see thinning of the ventricular wall.  

The patient ruled out for MI by troponins.

See this example:

Here there are QS-waves and an upright T-wave.  But it is not tall enough.  In all of leads V1-V4, the T/QRS ratio is far less than the optimal cutpoint of 0.36, so this does not represent acute anterior MI.
(The largest T/QRS ratio is in lead V2, at 5/29 = 0.17)  
This was an LV aneurysm.

See this example:

Here there are QS-waves, but the T/QRS ratio in both V3 and V4 is far higher than 0.36. 
In V3 the ratio is 5/6 = 0.83
This was an acute LAD occlusion.

Here are the details of this rule:

My rule for differentiating acute STEMI from LV aneurysm really only reliably distinguishes between:
1. acute STEMI on the one hand
2. subacute OMI or LV aneurysm on the other.

Therefore, if there has been continuous chest pain for more than 6 hours, a value less than 0.36 might be a false negative.

What is the rule?

First, there must be ST Elevation.
Second, the ECG differential diagnosis much be LV aneurysm vs. acute STEMI.

This rule should not be used for early repol vs. acute STEMI.  Conversely, if the differential is LV aneurysm vs. acute STEMI, then you should NOT use the early repol formula.

When should LV aneurysm be on the ECG differential diagnosis?  Primarily when there are well-formed Q-waves, with at least one QS-wave, in V1-V4.  A QS-wave is defined by absence of any R-wave or r-wave of at least 1 mm.  (If there is an R-wave or r-wave, we call the whole wave a QR-wave, Qr-wave, or qR-wave, depending on the relative size of the Q-wave vs. R-wave.)

The rule: If there is one lead of V1-V4 in which the T/QRS ratio is greater than 0.36, then acute STEMI is the likely diagnosis, though subacute STEMI is also possible.  Since both require the cath lab, if the ratio is greater than 0.36, and the clinical situation is right (i.e., unexplained chest discomfort), then cath lab activation is indicated.  I both derived and validated this formula, for which the cutoff has good sensitivity and specificity:
(accuracy of formula = 93.2%)
Validation full text 
Sensitivity 91%, specificity 81%

Why does this rule work?  Because Acute OMI has a large T-wave.

False negatives had pain duration greater than 6 hours. Thus, it may classify those patients with prolonged chest pain as LV aneurysm when they are really subacute STEMI.

See this incredibly interesting case:

ST Elevation: is it due to old MI (LV aneurysm) or to acute STEMI?

This case has some great bedside ultrasounds:

ST Elevation and QS-waves in a patient with Dyspnea

Another incredibly interesting case:

Subtle Anterior STEMI Superimposed on Anterior LV Aneurysm Morphology

Use ED Echo

ST elevation and QS-waves. ECG is equivocal. Use ED Echo!!

RBBB can fool you!

Dyspnea, Right Bundle Branch block, and ST elevation

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