Introduction

Acute obstruction of the left main coronary artery (LMCA) causes severe hemodynamic and electrical deterioration and often leads to the death of the patient.

Etiology

Occlusion or stenosis/obstruction of the Left main coronary artery. Most of the patients still have at least some flow in their LMCA, so the term “LMCA occlusion” is inaccurate. 

A complete LMCA occlusion would rapidly lead to STEMI, cardiogenic shock and death.

ECG features

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

ST elevation in aVR is not specific for LMCA occlusion and may indicate other conditions such as:

• Proximal left anterior descending artery (LAD) occlusion
• Severe triple-vessel disease 
• Diffuse subendocardial ischemia

 The mechanism of ST elevation in aVR is multifactorial:

• reciprocal to ST depression in I,II, aVL and V4-V6
• aVR directly records electrical activity from the right upper portion of the heart (the right ventricular outflow tract and the basal portion of the interventricular septum)
• diffuse subendocardial ischemia with ST depression in the lateral leads produces reciprocal change in aVR and infarction of the basal septum

The absence of STE in aVR almost entirely excludes a significant LMCA lesion.

Sinus tachycardia is an often presentation of LMCA occlusion, as patients do usually develop cardiogenic shock.

‍ECG 1 Critical stenosis of LMCA (diffuse ST depressions, ST elevation in aVR)

Management

• urgent revascularization, CABG or PCI
• UFH
• ASA
• P2Y12 if PCI indicated
• analgesia
• 02

References

1. https://practicingclinicians.com/the-exchange/left-main-coronary-artery-occlusion-st-elevation-in-avr
2. 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
3. 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.
4. Smith SW. Updates on the electrocardiogram in acute coronary syndromes. Curr Emerg Hosp Med Rep. 2013;1:43-52.
5. Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography. Hoboken, NJ: Wiley-Blackwell; 2009.
6. José A Prieto-Solís, Natividad Benito, Rafael Martín-Durán. Electrocardiographic Diagnosis of Left Main Coronary Artery Obstruction Using ST-Segment and QRS-Complex Vector Analysis. DOI: 10.1016/S1885-5857(08)60089-4
7. https://litfl.com/lmca-occlusion-st-elevation-in-avr/

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