Saturday, July 26, 2014

Is there excessively discordant ST Elevation in this ECG with Left Bundle Branch Block?

A patient complained of atypical chest pain and cough.  Here is his ECG:
There is sinus tachycardia at a rate of 120 with LBBB.  By the way, this is a New LBBB.  Where do we measure the ST elevation in the right precordial leads????  See below.



It is easy to find the J-point in lead V1, and all other J-points beneath it are simultaneous.  So I drew a line from the J-point directly down.  The intersection of the left side of this line with the tracing in leads V2 and V3 is the J-point.  It is 8 mm in V2 and 14 mm in V3.  

8 and 14 mm of ST Elevation!!  In a patient with new LBBB!

Surely this must be an acute anterior STEMI, no?

Again, the ECG is always proportional, with repolarization proportional to depolarization.  In this case, the S-wave in V2 is 42 mm and the S-wave in V3 is well over 60 mm (it goes far off the page).

Ratios:
V2: 8/42 is less than 0.20
V3: 14/(greater than 70) is less than 0.20

We found that a ratio greater than or equal to 0.25 was very sensitive and specific for coronary occlusion.  A value greater than 0.20 is almost always occlusion as well.

So the ratios are not excessive.  The ST elevation is proportional.  There is no STEMI, and there was indeed no MI in this case.

Another point: in LBBB, an increased heart rate will often increase the ST elevation.  So before coming to conclusions, it is wise to lower the heart rate.  In this case, the patient was dehydrated, so he received some fluids and his heart rate came down to about 95:
See the annotated EKG below



Now there is:
 V2: 5.5 mm of STE with a 35 mm S-wave (ratio = 0.16)
 V3: 7.0 mm of STE with a 57 mm S-wave (ratio = 0.12)


So BOTH the QRS voltage and the ST elevation voltage have come down, but the ratio has come down even more.

You may object: "the ST elevation ratio is dynamic!  There must have been a transient STEMI!!"

But this is not the case: tachycardia gives false + ST elevation in LBBB.  In this case, the ST elevation ratio is under the threshold of 0.20 - 0.25 both before AND after the heart rate is brought down.

Lessons:

1. Tachycardia elevates the ST segments in Left Bundle Branch Block
2. The significance of ST elevation depends on its proportion to the QRS
3. Finding the J-point in any one lead may be difficult.  Use the other leads to draw a vertical line to find it!

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