Introduction

The lateral wall of the left ventricle is supplied by branches of the left anterior descending (LAD) and left circumflex (LCx) arteries. 

STEMI of the lateral wall usually occurs as part of a larger territory infarction, e.g. anterolateral STEMI.

Lateral extension of an anterior, inferior or posterior MI indicates a larger territory of myocardium at risk with consequent worse prognosis.

Etiology

STEMI of the lateral wall is usually caused by acute atherosclerotic plaque rupture with subsequent thrombus formation in the left circumflex artery (LCx) or one of its branches (marginal branch). 

More commonly, left anterior descending (LAD) artery is involved in the ensuing anterolateral MI (diagonal branch). Ramus intermedius occlusion might be seen as well.

ECG manifestation

• ST elevation in the lateral leads (I, aVL, V5-6).
• Reciprocal ST depression in the inferior leads (III and aVF).
• ST elevation primarily localised to leads I and aVL is referred to as a high lateral STEMI ( usually caused by occlusion of the first diagonal branch of LAD)

Inferolateral STEMI - ST-elevation involving lateral (I, aVL, V5, V6) and inferior leads (II, III, aVF) -  usually seen with occlusion of the proximal LCx artery.

Anterolateral STEMI - ST-elevation involving lateral (I, aVL, V5, V6) and anterior leads (V1, V2, V3) - usually highly indicative of proximal LAD occlusion.

Management

• coronary angiography/PCI
• UFH
• ASA
• P2Y12 inhibitors
• nitrates
• 02

ECG 1 STEMI lateral (ST elevations I, aVL, V4-V6, ST depressions in inferior leads) - diagonal branch occlusion

ECG 2 STEMI of lateral wall (ST elevations in I, aVL, V5-V6) in a patient with occlusion of ramus intermedius

References

1. https://litfl.com/lateral-stemi-ecg-library/
2. Ludhwani D, Chhabra L, Goyal A, Quintanilla Rodriguez BS, Gupta N. Lateral Wall Myocardial Infarction. 2020 Sep 18. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan–. PMID: 30725913.
3. http://www.cardiology.org/tools/ecg_abnormalities/LMIK.htm
4. Ibanez B, James S, Agewall S, Antunes MJ, Bucciarelli-Ducci C, Bueno H, Caforio ALP, Crea F, Goudevenos JA, Halvorsen S, Hindricks G, Kastrati A, Lenzen MJ, Prescott E, Roffi M, Valgimigli M, Varenhorst C, Vranckx P, Widimský P. 2017 ESC Guidelines for the management of acute myocardial infarction in patients presenting with ST-segment elevation: The Task Force for the management of acute myocardial infarction in patients presenting with ST-segment elevation of the European Society of Cardiology (ESC). Eur Heart J 2018;39:119–177.