Lateral STEMI: leads I, aVL, V5, V6 involvement
Lateral STEMI involves the lateral wall of the left ventricle, typically supplied by the left circumflex artery (LCx) or the diagonal branches of the LAD. ST elevation appears in leads I, aVL (high lateral) and/or V5–V6 (low lateral).
High lateral STEMI (I, aVL only): the most commonly missed lateral STEMI pattern. ST elevation isolated to leads I and aVL without involvement of other precordial or inferior leads is subtle and frequently overlooked on initial triage review. Reciprocal ST depression in leads III and aVF confirms the diagnosis.
Anterolateral STEMI (V1–V6 + I, aVL): extensive lateral involvement — large circumflex or combined LAD-circumflex territory. Highest-risk lateral pattern.
Reciprocal changes: inferior ST depression (in II, III, aVF) typically accompanies lateral STEMI when aVL is elevated. The aVL-to-III relationship is important: any time you see ST depression in III and the patient has chest pain, assess lead aVL for reciprocal confirmation of high lateral STEMI.