Wednesday, January 22, 2014

Look at the PVCs!!

An elderly woman presented with chest pain.  She was hemodynamically stable.  Here is her initial ECG:
There is bigeminy.  There is high voltage.  There is ST elevation in the normal beats.  Is this STE baseline, due to the high voltage??  How about the PVCs?  
The computer read: "ST elevation: MI vs. pericarditis vs. early repol."  
What do you think?  See below.




















There are a few findings which are all but diagnostic of anterior STEMI:

1. The PVCs, which normally have discordant ST segments (just like Left Bundle Branch Block), have proportionally excessively discordant ST elevation.  The ST elevation in the PVC in V4 is 5.5-6 mm at the J-point.  The preceding S-wave is 21 mm.  The proportion is thus 25% or more (the normal is much less than 20%).  Furthermore, the T-wave is enormous (hyperacute!)  While there is no proof that the rule applies to PVCs, as it does to LBBB, in my experience it is very similar but slightly less specific.

2. Perhaps more importantly, the T-waves in the PVCs from V3-V6 are enormous (hyperacute).  They are far more massive than any typical PVC.

3. There is a fragmented QRS in the PVC in lead V2, similar to Cabrera's sign, which is fairly specific for MI (either new or old) in the presence of LBBB, and probably also in a PVC. 

4. Finally, there is also ST elevation in the beats with a normal QRS.  There are 1.5 mm of STE at the J-point in V2 and 2 mm in V3.  These meet the 2013 guidelines for STE in women (at least 1 mm in 2 consecutive leads, but at least 1.5 mm in V2 and V3).  "Criteria," as I have stated before, are not very sensitive or specific, but in an elderly woman, this much ST elevation is rarely normal.  On the other hand, the high voltage could lead to a false positive.

The findings in the PVCs are the most convincing findings for STEMI.


How would the formula for differentiating "normal variant" ST elevation from STEMI perform on this ECG (see sidebar excel applet or "SubtleSTEMI" iPhone app)?  For those who want to see its performance, here goes:  The computerized QT was 462 ms and QTc was 515 ms.   Into the formula, enter 3 mm for ST elevation at 60 ms after the J-point in lead V3, 515 for the QTc, and 27 mm for the R-wave amplitude in V4.  The result is 25.17, which would indicate STEMI.  This QT, however, is obviously both a misread (of the QT, which is really only 420 ms) and of the QTc [which is the QT divided by the square root of the PRECEDING R-R interval.  In this ECG, the R-R interval preceding the normal beats (not preceding the PVCs) is 1100 ms, so the QTc MUST be less than the QT).  I calculate the QTc as 400 ms.  So, using my manually derived numbers, the formula comes to 18.38, which would not be STEMI. 




The physician who saw the patient was alarmed by these PVCs, and so ordered a serial ECG just 12 minutes later:
Now there is a clear increase in the ST elevation of BOTH the normal QRS beats and the PVCs.  The ST/S ratio in the PVC in lead V4 is now 9/15 = 0.60, clearly diagnostic of STEMI.  


How about the formula now?  The Computerized QT was 440ms, and QTc = 511.  It seems to be misread again: I get 400ms for the QT, and QTc of 460ms.  Now the STE is 5 mm and R-wave in V4 is 23 mm.  If I use the formula with the computer's QTc, the value is 28.6 (very high). If I use my QTc, the value = 25.6 (still a STEMI).  Now, no matter which numbers are used for the formula, it indicates STEMI

The cath lab was activated and a 100% mid LAD occlusion was found and opened.


The physician who saw this patient had been to several of my lectures on anterior STEMI, and sent this with the quote, "Probably not the first time, but your lecture helped in saving another life."  I quote this only to demonstrate that these morphologies can be studied and learned, and ECG interpretation can improve with learning and practice.

Lesson:

Use the PVCs to diagnose STEMI.   

Here are some other cases, including a video lecture by Dr. Wang of the "Usefulness of PVCs".




The cover of Dr. Wang's new book shows a STEMI that is seen best in the PVC:



 

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