Tuesday, May 4, 2021

Let's Use Aslanger's simplified formula on this case (simplified Smith LAD occlusion/early repol formula)

This was posted in August 2019:  Acute Chest pain in a 50-something, and a "Normal" ECG

Chris Mondie of the Newark Beth Israel Emergency Medicine Residency sent this case

A 50-something man presented with acute chest pain.

Here is his ECG:
As you can see, the computer said "normal" and it really does have a normal appearance to those who have not been reading this blog regularly.
The ST Elevation in precordial leads does not meet STEMI criteria.  Both V2 and V3 are less than 2 mm, which is the cutoff for males over age 40.
We discussed this at the time (and I have copied and pasted that discussion below), and we used the 4-variable formula to show that it is an LAD occlusion.

But Aslanger has modified and simplified my formula, and I have not discussed it enough.

The primary benefit of the modification is that the QT need not be corrected.  This is particularly important because the computerized QTc is different on different computers, with any one of the 4 correction formulas used, and the choice of formula is not obvious.  On our EKGs, I had to reverse engineer to find out that it uses Hodges formula, not Bazett. 

Aslanger E et al.  A Simplified Formula Discriminating Subtle Anterior Wall Myocardial Infarction from Normal Variant ST-Segment Elevation.  American J Cardiol 122(8):1303-1309; Oct 2018.

Here is that simplified formula: (RAV4 in mm + QRSV2 in mm) - [(QT in mm) + STE60V3 in mm)

In this case:
QT = 360 ms (QTc = 385).  360 ms =  9 mm.
STE60V3 is at least 4.0 mm, maybe more
RAV4 = 6
QRSV2 = 18


A value less than 12 corresponds to LAD occlusion; a value greater than 12 to normal variant STE

Let's plug the numbers into the formula:
18 + 6 = 24; 9 + 4 = 13;  24 - 13 = 11, which is below 12, so LAD occlusion.


Previous Discussion:

An interpretation of "normal" could, of course, deceive many providers.

Analysis

This could be normal variant ST Elevation in V2 and V3.  There is 1.5 mm STE in at the J-point in lead V2 (relative to QRS onset, otherwise known as PQ junction).  There is 1.0 mm in V3.

So this is a normal amount of STE in V2 and V3, defined by Universal Definition of MI as up to 2.0 mm in men over age 40.  So there is definitely no STEMI, and the STE is normal.  So the computer is correct in calling it normal.

But after reading this blog, you all know that most OMI do NOT meet STEMI criteria.  Some patient's baseline ECG has zero STE.  Some patient's baseline has normal variant STE.  You don't know which kind of patient this is.

Some normal STE is actually due to OMI.  Some normal STE is not due to ischemia at all.

It is your responsibility to determine if STE is ischemic or not.

How do we do so?

Use the formula.

QTc = 385
STE60V3 is at least 4.0 mm, maybe more
RAV4 = 6
QRSV2 = 18

Formula value = 19.94 (very high, indicating LAD occlusion).

Any value greater than 18.2 is likely to be LAD occlusion.

For graphs of sensitivity, specificity, and accuracy at various cutoffs, see this post:

More precise interpretation of the results of the 4-variable formula.


12 Example Cases of Use of 3- and 4-variable formulas to differentiate normal STE from subtle LAD occlusion


Chris Mondie's note:

"My read: Acute proximal LAD occlusion. Hyperacute T waves which tower above the preceding R waves, poor precordial R wave progression. Large T in V1.  Smith subtle LAD equation indicative of acute LAD occlusion. 

"Bedside echo revealed anteroseptal wall motion abnormality at which point I activated a code STEMI. 

"Cardiology agreed to take the pt to the lab but thought it would likely be negative. 

"100% proximal LAD successfully stented. 
Defibrillated out of v fib in the cath lab. 
Initial TnI was negative. 

"I thank you for constantly updating your blog and allowing free open access education on EKG interpretation. I recognized this as a STEMI immediately and I was only able to do so solely because of your blog."















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