Left Main Coronary Artery Occlusion: ST Elevation in aVR

Left Main Coronary Artery Occlusion: ST Elevation in aVR Posted By:
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During my ECG training, we were taught that the findings from lead aVR were only important for supportive evidence of pericarditis. I subsequently learned differently. This post will look at ECG findings associated with left main coronary artery (LMCA) disease and explore the significance of ST-segment elevation in the aVR "forgotten lead."

Early identification of LMCA disease is critical because acute occlusion can cause rapid hemodynamic and electrical deterioration. LMCA insufficiency due to critical stenosis of the left main artery is important to recognize because these patients can progress to complete occlusion and are likely to require surgical intervention, such as CABG.

The mechanism of ST elevation (STE) in aVR is multifactorial. Lead aVR is electrically opposite to the left-sided leads I, II, aVL, and V4-6; therefore, ST depression in these leads will produce reciprocal ST elevation in aVR. Additionally, lead aVR directly records electrical activity from the right upper portion of the heart. This includes the right ventricular outflow tract and the basal portion of the interventricular septum, so infarction in this area could theoretically produce ST elevation in aVR. Diffuse subendocardial ischemia with ST depression in the lateral leads produces reciprocal change in aVR and infarction of the basal septum (ie, a STEMI involving aVR).

ST elevation in aVR is not entirely specific to LMCA occlusion. It may also be seen with:

  • Proximal left anterior descending artery (LAD) occlusion
  • Severe triple-vessel disease (3VD)
  • Diffuse subendocardial ischemiaie, due to O2 supply/demand mismatch, following resuscitation from cardiac arrest

Note: Some of the authors argue that using the term "LMCA occlusion" is inaccurate, as most of these patients have at least some flow in their LMCA (ie, incomplete LMCA occlusion) whereas a complete LMCA occlusion would rapidly lead to STEMI, cardiogenic shock, and death.

Typical ECG findings with LMCA occlusion:

  • Widespread horizontal ST depression, most prominent in leads I, II and V4-6
  • ST elevation in aVR ≥1mm
  • ST elevation in aVR ≥V1

Review this ECG in a patient with acute chest pain:

ECG of acute chest pain

There is diffuse ST depression, with ST elevation in aVR. This is diffuse subendocardial ischemia. The ST elevation in aVR is reciprocal to the ST depression vector that is directed anterior, lateral, and inferior (toward leads II and V5). STE in aVR is thus reciprocal ST elevation!

ST-elevation myocardial infarction involving the left main coronary artery has been associated with significant morbidity and mortality. When reviewing ECGs in patients with chest pain, always be on the lookout for this phenomenon.

References
  • Baek JY, Seo SM, Park HJ, Kim PJ, et al. Clinical outcomes and predictors of unprotected left main stem culprit lesions in patients with acute ST segment elevation myocardial infarction. Catheter Cardiovasc Interv. 2014;83:E243-E250.
  • Smith SW. Updates on the electrocardiogram in acute coronary syndromes. Curr Emerg Hosp Med Rep. 2013;1:43-52.
  • Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography. Hoboken, NJ: Wiley-Blackwell; 2009.
  • Knotts RJ, Wilson JM, Kim E, Huang HD, Birnbaum Y. Diffuse ST depression with ST elevation in aVR: Is this pattern specific for global ischemia due to left main coronary artery disease? J Electrocardiol. 2013;46:240-248

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Filed under: Cardiometabolic

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