How does acute left main occlusion present on the ECG?

Post by Smith and MeyersSam Ghali (https://twitter.com/EM_RESUS) just asked me (Smith):" Steve, do left main coronary artery *occlusions* (actual ones with transmural ischemia) have ST Depression or ST Elevation in aVR? "Smith and Meyers answer:First, LM occlusion is uncommon in the ED because most of these die before they can get a 12-lead recorded.But if they do present:The very common presentation of diffuse STD with reciprocal STE in aVR is NOT left main occlusion, though it might be due to subtotal LM ACS, but is much more often due to non-ACS conditions, especially demand ischemia.  In these cases, STE in aVR is always reciprocal to the ST depression of subendocardial ischemia elsewhere (ST depression vector towards II and V5).Total LM occlusion can present withSTEorSTDin aVR. When total LM occlusion does present with STE in aVR, there is ALWAYS ST Elevation elsewhere which makes STEMI obvious; in other words, STE is never limited to only aVR but instead it is part of a massive and usually obvious STEMI.  The pattern seen may, or may not, be unique to left main occlusion.  Some total LAD occlusion manifest on the ECG similarly to some left main occlusions.  All are, however, clearly massive STEMI.To reiterate the most important part relevant to your question:LM occlusion does not present withisolatedSTE in aVR.  Depending on where the STE vector of the LM occlusion shows up on the ECG, there...
Source: Dr. Smith's ECG Blog - Category: Cardiology Authors: Source Type: blogs