LMCA

Left main coronary artery occlusion or aVR OMI is a very rare finding. ST elevation in aVR itself is not uncommon, however, and can be found with:

proximal LAD occlusion
severe triple-vessel disease
diffuse subendocardial ischemia

The most common cause of ST elevation in aVR is reciprocal to subendocardial ischemia; lead aVR does not actually account for ventricular wall (only atria), so ST elevation here is not the same as ST elevation in other leads. When aVR has ST elevation in the setting of a OMI, the vast majority of the time it is not a left main coronary artery occlusion, but found with other OMIs (primarily anterior). When aVR has ST elevation >1mm in the setting of anterior OMI, it is a poor prognostic finding as it indicates a proximal occlusion covering a lot of myocardium and potentially multivessel occlusion requiring CABG. The amount of ST elevation in this setting correlates with worsened mortality as well.

Septal OMI with ST elevation in aVR, indicating a proximal LAD occlusion.

This patient presented with GI bleed and chest pain. His chest pain improved with blood transfusion. This is more typical findings of ST elevation in aVR as it is secondary to diffuse ST depressions from demand ischemia.

Patients with true LMCA occlusion/aVR OMI are patients in cardiac arrest or peri-arrest as the amount of myocardium supplied is too great to not have cardiogenic shock. Another reason for this being so rare is that many of them do not survive long enough to get a 12-lead EKG. To be able to diagnose an 'aVR OMI', one needs:

widespread ST depression at least 1mm in at least 6 leads
ST elevation in aVR at least 1mm
ST elevation in aVR>ST elevation in V1

There needs to also be ST elevation in other leads (primarily V1). The patient generally does not have ST depression in all other leads as that is more typical of diffuse subendocardial ischemia from another cause (ie sepsis, GI bleed). Subendocardial ischemia producing ST elevation in aVR is also common with significant tachycardia. In contrast, anterior OMI with new RBBB and LAFB are highly suggestive for LMCA occlusion.

Actual LMCA OMI. This patient presented in cardiogenic shock and had multiple runs of VT. Note the slight ST elevation in V1 and that STE in aVR>V1.

Another LMCA OMI. This patient presented in cardiogenic shock and had VF before transport to the cath lab.

This patient had a LMCA occlusion. Note that there is minimal ST elevation in aVR, though it is present in some of the anterior and high lateral leads. There is a new RBBB and LAFB.