A middle-aged male diabetic who is otherwise healthy was found unconscious by his wife, with incontinence. He quickly awoke but was too weak to stand. Initial vitals by EMS were BP 100/50 with pulse of 80 and normal glucose. He remained weak and somnolent, and without focal neurologic abnormality. He recovered full consciousness, but still felt weak and “not normal.”
There was a prehospital ECG:
|What do you think?
He arrived in the ED and had this ECG recorded:
|This one was sent to me for my opinion.
I looked at it without any clinical information.
What do you think?
I wrote back that this is diagnostic of hypokalemia.
It turned out the K was 2.6 mEq/L.
Why did I say this?
There is scooped ST depression in multiple leads, very typical of hypokalemia: I, II, aVL, V4-V6.
There are large U-waves. Look particularly in V1 and V2. This results in the appearance of down-up T-wave in V2; however, if it is a T-wave, resulting QT interval would be impossibly long. Thus, it is a large U-wave, and the apparent QT interval is a QU interval. Look directly above at V1 and you can see the U-wave clearly.
Such downsloping ST depression in V2 may frequently be misinterpreted as posterior STEMI (reciprocal to ST elevation of the posterior wall).
The patient had no chest pain or SOB. His initial lactate returned at 5.0 mEq/L. The patient and the vital signs completely recovered. He seemed completely well.
After the K returned at 2.6, it was replaced.
The initial troponin I was 0.096 ng/mL, then rose to 0.191 at 2 hours after the first, and a second ECG was recorded 220 minutes after the first:
|ST depression has resolved.
K has been replaced.
The third troponin I returned at 4 hours at 3.002 ng/mL, at which time the K was normal and another ECG was recorded that is not changed from the 220 minute one.
A 4th troponin returned at 6 hours at 7.905 ng/mL.
The clinicians decided to get a CT of the chest/abdomen/pelvis (I am not certain what they were looking for). One image of the heart is shown here:
|The arrows point to the inferior subendocardium. It is dark because there is low contrast enhancement, which indicates absence of blood flow.
This is a picture of inferior subendocardial ischemia.
Here is a closer up axial (transverse) view of the heart:
|The arrows point to a subendocardial region with poor contrast enhancement due to ischemia.
This is posterior subendocardial ischemia.
This finding was seen in real time, and the patient was started on treatment for NSTEMI.
A repeat ECG was unchanged, and the potassium returned normal. Thus, in the presence of a normalized K, the ECG normalized in spite of ongoing myocardial ischemia.
A formal echo was done, which showed:
Regional wall motion abnormality (RWMA) of the apex, with dyskinesis (aneurysm)
RWMA of the distal inferior wall
A coronary angiogram was done a few hours later:
Culprit Lesion: 99% stenosis of the mid Circumflex with TIMI 1-2 flow (obstructed)
This was thrombus, acute (not a chronic lesion)
Diffuse severe disease of the mid and distal LAD
Chronic total occlusion of the mid right posterior descending artery (off the RCA) with left to right collateral filling
Three vessel coronary artery disease with probable mid circ culprit for NSTEMI.
Successful circumflex PCI with excellent angiographic result, 0% residual.
If the source of collateral filling from the “left” was the circumflex, then the PCI of the circ would have restored this flow and resulted in full reperfusion to the inferior wall in addition to the posterior wall.
Here is a post PCI ECG:
|Normal ST elevation in V2, not ST depression
Also: Now there is a large T-wave in V2 (posterior reperfusion T-wave) and inverted T-waves in inferior leads II, III, aVF (inferior reperfusion).
This is good evidence for reperfusion of the inferior and posterior walls.
So what happened?
There were several clinicians who thought the the ST depression was due to posterior STEMI. It is possible but I think unlikely.
1. We do not have any evidence that there ever was full STEMI of the posterior wall. The CT scan only shows subendocardial ischemia, which would not present with ST depression in lead V2.
2. The ECG looks to me like hypokalemia, and the K was 2.6 mEq/L.
3. The artery was open with flow at angiogram, corresponding to the subendocardial ischemia (not to transmural ischemia, which would lead to STEMI on the ECG) –though it is possible that the artery was fully occluded at the time of the first 2 ECGs.
4. There never was any chest pain or SOB or other anginal equivalent (and this was not a very elderly or debilitated person who might only feel “weak” with his MI, though he is diabetic).
5. The ECG normalized with a normal potassium while the myocardial ischemia was ongoing.
Initially when I heard about the case, I knew only these 4 things:
1. I saw the ECG, thought it was diagnostic of hypokalemia and confirmed it by the K of 2.6
2. I knew the troponins were elevated
3. I had heard only this about the angiogram: that there was a 99% circumflex lesion.
With this information, I surmised that the syncope was due to ventricular tachycardia from hypokalemia and the elevated troponins were from demand ischemia (type II MI) due to hypotension (because of VT) and poor flow through an extremely narrow chronic circumflex stenosis.
However, this was erroneous, as it turned out that the circumflex lesion was definitely due to acute thrombus (ACS), not a chronic lesion (as existed in the RCA).
Thus, one can only say that there were 2 pathologies at once:
1. Acute coronary syndrome of the circumflex with acute myocardial ischemia, that manifested without any chest pain or SOB, and that probably was not manifesting on the ECG. [Although the scooped ST depression could have been a manifestation of diffuse subendocardial ischemia, all of it resolved with replenishment of the K in spite of the fact that the myocardial ischemia was ongoing.]
2. Hypokalemia, that did manifest on the ECG.
Hypokalemia in the presence of myocardial ischemia is a very strong risk factor for acute ventricular dysrhythmia, so it is very likely that the syncope was due to ventricular tachycardia (VT).
Here are down-up T-waves of posterior MI:
Here is down-up “T-waves” of hypokalemia: