Monday, April 14, 2014

Anterior STEMI?

The patient presents to the emergency Department with complaints of substernal left-sided chest pain present for 4 days but worse in the last 24 hours.

Here is his ED ECG:

The computerized QTc is 451.  What do you think?  The previous ECG, with interpretation, is below.

Here is the Previous ECG.
My reading was printed on the ECG as "probable benign T-wave inversion."    I had discharged the patient at his previous visit.  His presentation had not been concerning for ACS and his ECG was, to me, a benign variant.

The physicians were appropriately worried about the previous ECG and used the formula (see sidebar Excel applet) and came out with a value above 23.4  (I cannot remember what the value was, but they did use 3 mm for the STE variable).

When I apply the formula, even if I use 3 mm as the ST elevation as 60 ms after the J-point, and use R amplitude in V4 at 22 mm, I get 23.03 (which is less than 23.4 and thus indicates early repol).  Furthermore, the morphology of V4 is nearly diagnostic of "Benign T-wave inversion."

In general, if there is T-wave inversion, I do not recommend using the formula. Patients whose ECGs had T-wave inversion in V2-V5 were excluded from the study because T-wave inversion, as a general rule, should imply MI.  However, if you are familiar with the morphology of Benign T-wave Inversion (BTWI), then you would see that these ECGs manifest probable BTWI and be less worried about the ST Elevation.

As for the formula, when you get a value that is close to 23.4, it is wise to not rely on it too heavily.  The sensitivity and specificity of 23.4 was close to 90%, but I the closer the value is to 23.4, the less sensitive and specific it is.

Appropriately, they ordered a 2nd ED ECG about 20 minutes later:
QTc is 445

They thought there might be more STE in lead V3.  I do not see any significant change.

They were still worried, but instead of activating the cath lab, they appropriately consulted the cardiologist and together decided on an immediate formal echocardiogram.

The echo showed:

--Normal left ventricular size, mild concentric left ventricular hypertrophy and hyperdynamic systolic function.
--The estimated left ventricular ejection fraction is 75 %.
--No left ventricular wall motion abnormality identified.
--Normal right ventricular size and function.

The patient was admitted and ruled out for MI.

Benign T-wave Inversion (this link takes you to many examples)

There are many etiologies of T-wave inversion.  We are most worried about ischemic T-wave inversion.  Wellens' syndrome is particularly dangerous, as it signifies an unstable critical LAD stenosis.  I have several posts on this; here is one that shows the entire evolution.

Another etiology is "Benign T-wave Inversion", which has long been recognized. I first saw it described in Chou's textbook.  It is a normal variant associated with early repolarization.  K. Wang recently studied it.  He reviewed ECGs from all 11,424 patients who had at least one recorded during 2007 at Hennepin County Medical Center (where I work) and set aside the 101 cases of benign T-wave inversion.  97 were black.  3.7% of black men and  1% of black women had this finding.  1 of 5099 white patients had it.  Aside from an 8.8% incidence (9 of 109) black males aged 17-19, it was evenly distributed by age group.

I have reviewed these 101 ECGs, and what strikes me is:

1. There is a relatively short QT interval (QTc < 425ms)  (this case would be an exception!)
2. The leads with T-wave inversion often have very distinct J-waves.
3. The T-wave inversion is usually in leads V3-V6 (in contrast to Wellens' syndrome, in which they are V2-V4)
4. The T-wave inversion does not evolve and is generally stable over time (in contrast to Wellens', which always evolves).
5. The leads with T-wave inversion (left precordial) usually have some ST elevation
6. Right precordial leads often have ST elevation typical of classic early repolarization
7. The T-wave inversion in leads V4-V6 is preceded by minimal S-waves
8. The T-wave inversion in leads V4-V6 is preceded by high R-wave amplitude
9. II, III, and aVF also frequently have T-wave inversion. 

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