This is the conclusion to the Snapshot Case from a couple of days ago. If you haven’t already done so, I suggest reviewing the very brief initial case description.
Here again is the EKG from Tuesday’s case.
This tracing is nearly pathognomonic for true occlusion of the left main coronary artery (LMCA), resulting in a “left main STEMI.”
Since this a Snapshot case with no follow-up this diagnosis cannot be confirmed, but it is a rather unique pattern I have yet to see mimicked by any other form of ACS. I’m not surprised that few, if any, readers were familiar with this presentation. It is not commonly taught, and in fact I only came across it from seeing a few cases and reading case reports. Let’s review the pattern of ST-deviation that we are seeing…
First, consider the limb leads.
There is massive ST-elevation in leads I and aVL with massive reciprocal ST-depression in leads II, III, and aVF. This pattern is consistent with STEMI of either the left main (LMCA), left anterior descending (LAD), or circumflex (LCx) coronary artery. Though there is really no way to differentiate them using the limb leads alone, the magnitude of the ST-elevation enough to produce a true “tombstone” pattern in I and aVL certainly suggests a large area of ischemic myocardium consistent with the LAD or LMCA.
For those following my 360 Degree Heart series, here’s what the leads look like displayed in that fashion (though it adds nothing to the diagnosis here).
Though informed by the limb leads, the probable diagnosis here resides in the precordial leads. The ST-elevation is maximal in V2 and extends out to V4-V6 with reciprocal ST-depression in V1.
This pattern could be somewhat consistent with an isolated lesion in the LAD but there is a problem: a typical LAD occlusion should not have ST-depression in V3, especially if there is ST-elevation extending all the way out to V6. Seeing no ST-elevation in V3, maybe even a little ST-depression, when there is a large amount of ST-elevation in the rest of the classic “anterior” leads is a big issue. It’s right to consider that perhaps V2 and V3 have been swapped, but based on how the rest of the tracing plays out I can tell you that is not the case here.
The pattern could also be considered consistent with an LCx culprit, and the large amount of ST-elevation in V2 certainly suggests that (V2 is a “high-lateral” lead, believe it or not), but there is a bit too much elevation in V4-V6. Though this latter territory is often considered part of the lateral wall (a pun?), it’s actually pretty low [caudal] on the heart compared to the area the LCx and its branches typically serve and is really part of the antero-apical region supplied by the LAD.
In this case the real lynchpin for me is V3. A lot of findings are pointing towards an LAD culprit but that sudden loss of elevation in V3 sticks out like a sore thumb. I’m left to conclude that there should be anterior ST-elevation in V3 with our LAD occlusion but some other force is acting to cancel it out; that force is posterior STEMI from a LCx occlusion as well. Combine the anterior ST-elevation of an anterior STEMI with the posterior elevation of a large posterior STEMI and they can cancel one-another out, leaving a net of almost no ST-deviation.
So what we have here is a mixed STEMI picture with features consistent with both LAD and LCx occlusion, and that’s exactly what is causing it. The LMCA supplies both the LAD and the LCx, so a true occlusion of the left main essentially creates a STEMI of both those territories. [You could also have a dual-culprit STEMI with culprits in both the LAD and LCx but that is rather rare, even when compared to LMCA STEMI.]
Also consistent with LMCA STEMI is the presence of right bundle branch block (RBBB) and left anterior fascicular block (LAFB) in a pattern of bifascicular block. Given the marked STEMI this is probably an acute finding and fits the picture of ischemia involving a massive area of the myocardium (and is also associated with a markedly increased mortality).
“But LMCA occlusion presents with diffuse ST-depression and ST-elevation in aVR and V1!”
Despite the extremely prevalent teaching, that finding is actually what you see with diffuse NSTEMI, sometimes involving the LMCA, and usually with a less-than-total culprit lesion; whereas what we see here is LMCA STEMI with a complete or near-complete occlusion of the LMCA. For more on the diffuse subendocardial ischemia seen in LMCA NSTEMI see my prior post here.
“I still don’t believe you.”
That’s fine, but I highly suggest checking out these other cases with very similar patterns of ST-deviation.
- Dwyer N, Kanani R. Images in clinical medicine. Left main coronary artery thrombosis. N Engl J Med [Internet]. 2012 Apr 5 [cited 2014 Dec 12]; 366:e21. Available from: http://www.nejm.org/doi/full/10.1056/NEJMicm1105065
- Joumaa MA, Davis T, Rosman H. Acute left main coronary artery occlusion: a catastrophic problem with poor prognosis. J Invasive Cardiol [Internet]. 2006 Jun [cited 2014 Dec 12]; 18(6):E179-80. Available fromÂ http://www.invasivecardiology.com/articles/acute-left-main-coronary-artery-occlusion-catastrophic-problem-poor-prognosis
- Goktekin O, Unalir A, Gorenek B, Kudaiberdieva G, Cavusoglu Y, Melek M, Aslan R, Timuralp B. Traumatic Total Occlusion of Left Main Coronary Artery Caused by Blunt Chest Trauma. J Invasive Cardiol [Internet]. 2002 Aug [cited 2014 Dec 12]; 14(8):463-5. Available from http://www.invasivecardiology.com/articles/traumatic-total-occlusion-left-main-coronary-artery-caused-blunt-chest-trauma
- Smith, SW. Dr. Smith’s ECG Blog [Internet]. Minneapolis; 2008-2014. The difference between Left Main occlusion and Left Main insufficiency. 2014 Aug 2 [cited 2014 Dec 12]. Available from http://hqmeded-ecg.blogspot.com/2014/08/the-difference-between-left-main.html
- Fiol M, Carrillo A, Rodriguez A, Pascual M, Bethencourt A, Bays de Luna A. Electrocardiographic changes of ST-elevation myocardial infarction in patients with complete occlusion of the left main trunk without collateral circulation: differential diagnosis and clinical considerations. J Electrocardiol. 2012 Sep; 45(5):487-90.
- Granda Nistal C, Rubio Alonso B, MejÃa MartÃnez E, Blazquez Arroyo L, Coto Morales B, Parra Fuertes JJ, Garcia Tejada J, Hernandez HernÃ¡ndez F, VelÃ¡zquez MartÃn MT, Gonzalez-Trevilla AA. Left Main Dissection and Pseudoaneurysm Formation After a Road Traffic Accident. Circulation. 2015 Sep 15;132(11):e143-5.