A 70-something woman with syncope and a wide complex

This case was written by Andy Lichtenheld (https://twitter.com/ALichtenheld), a really smart 2nd year resident here at our Emergency Medicine program at Hennepin County Medical Center.  

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A 70-something woman with a history of CAD arrived by EMS after a syncopal episode. She had been in her usual state of health when she suddenly became lightheaded and collapsed. She regained consciousness prior to EMS arrival and arrived in the ED confused but gradually clearing. She had no chest discomfort, shortness of breath, arm pain, jaw pain or any other symptoms.
An initial ECG was recorded:
What do you think?
The computer has identified it as sinus with a Mobitz I AV block with a LBBB.   
However, both the rhythm and QRST appear to be more complicated.  
Rhythm: Regular P-waves can be seen throughout the rhythm strip. Without using calipers and without using more thought than necessary in an emergency, it is hard to say whether this is first or second degree AV block with conduction to a left bundle branch block, or if it is third degree (complete) heart block with an escape from the right ventricle.  Beats 3 and 5 are PVCs.   
Smith: After scrutinizing at leisure, I do think it is complete heart block with an RV escape, but it is complicated.
What else?
There is excessively discordant ST elevation in V1 & V2.  ST/S ratio in V1 is 5/15 = 33%.
There is excessively discordant ST elevation in aVR.  The ST/S ratio is 3/8 = 37%.
There is also excessively discordant ST depression in lead I (ST/R ratio = 100%) and V4 (ST/R ratio = ~60%).
If you accept, as Dr. Smith does, that the Smith Modified Sgarbossa criteria can be used not only in LBBB, but also in ventricular escape rhythms, then any one of these findings meets those criteria.  The STE in V1 as well as the STD in I and V4 are particularly specific for occlusion.
Furthermore, there is an abnormal amount of STD in V5 and V6 (ST/R ratio almost 20%).
Smith Modified Sgarbossa Criteria for LBBB and Ventricular Paced Rhythms

Rule 1: (80-90% sensitive, 95% specific for occlusion)
Any one of:
1. 1 mm concordant STE in any one lead
2. 1 mm concordant STD in any one of V1-V3
3. At least 1 mm discordant STE that is ≥25% of the preceding S-wave in at least one lead
Rule 2: (Only 64% sensitive, but 98% specific for occlusion)
Any one lead with proportionally discordant STE or STD of at least 30% of the preceding R- or S-wave
Smith comment

One more finding!!   PVCs!!!!   The 5th beat is a PVC and has an RBBB morphology (large R-wave in aVR with wide S-wave in V5).  This implies a PVC originating in the left ventricle.  RBBB morphology PVCs should never have an ST segment that is concordant to the QRS, as it is here in lead aVR.  This is diagnostic for STEMI.

See these cases:

Case continued
A previous ECG was obtained:
There is a preexisting LBBB with proportionally normal discordant ST elevation, which makes the ST changes in the new EKG obvious by comparison.

This also suggests that the rhythm in the first ECG is supraventricular, because the QRS morphology is LBBB.  However, if you look closely at V5 and V6 in the first ECG, both have a very narrow peak compared to this old ECG which is much more typical LBBB.
Smith comment: I am still not completely certain as to whether the first ECG is supraventricular with left bundle branch block, or with RV escape.  But it does not matter: the patient has a coronary occlusion until proven otherwise.  She needs immediate pacer pad placement and angiography/PCI.
Case Continued
The clinicians caring for the patient were concerned about an acute coronary occlusion. The cardiologist was in hospital and was paged to the resuscitation area. Over the course of the following few minutes, the patient gradually recovered to her normal mental status. She remained normotensive and entirely asymptomatic. 

As the cardiologist arrived, a change in the QRS morphology was noted on the monitor and a repeat ECG was obtained:
What is your interpretation?
Now there is definitely complete heart block with a ventricular escape:
–The predominant QRS morphology is now RBBB + LAFB with interposed PVC’s, which indicates a dominant escape focus now in the left posterior fascicle.
–The ST elevation in V1 and V2 with reciprocal ST depression are now obvious.  It is RBBB morphology with ST elevation concordant to the R-wave, similar to the PVC mentioned above.  This does not happen without ischemia.
–There is marked ST depression in lead II which is then attenuated in aVF and then entirely absent in lead III.  
Smith comment: What is the infarct artery???  With STE in V1 and aVR, one might think this is LAD or left main. Such a conclusion would be consistent with the diffuse ST depression.  
The ST axis is exactly towards aVR, which is what you expect with diffuse subendocardial ischemia (ST depression vector towards I and II, with a reciprocal ST elevation vector towards aVR).  However, the ST elevation is so much more pronounced than the ST depression.  
Is there something else going on??
Andy Lichtenheld wrote: “This is also consistent with inferior and large RV MI due to proximal RCA occlusion.”
Case continued:
The initial troponin I returned elevated at 4.5 ng/mL.
She was taken to the cath lab where a 90% proximal RCA lesion, proximal to the RV marginal branch, was stented and a temporary pacemaker was placed.
The next day echo showed very poor LV function with an inferior wall motion abnormality.
Smith comment: 
So Dr. Lichtenheld was correct.  It was an inferior + right ventricular (RV) STEMI.
This pattern of ST elevation and depression is often due to LAD or left main.
I can’t fully explain why there was no ST elevation in the inferior leads, especially lead III.
See this case: 

Septal STEMI with ST elevation in V1 and V4R, and reciprocal ST depression in V5, V6

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