The site of LAD occlusion (proximal versus distal) predicts both infarct size and prognosis.
#Proximal LAD / LMCA occlusion has a significantly worse prognosis due to larger infarct size and more severe haemodynamic disturbance.
The site of occlusion can be inferred from the pattern of ST changes in leads corresponding to the two most proximal branches of the LAD: the first septal branch (S1) and the first diagonal branch (D1).
#Territories
S1 supplies the basal part of the interventricular septum, including the bundle branches (corresponding to leads aVR and V1)
D1 supplies the high lateral region of the heart *Occlusion proximal to S1
Signs of basal septal involvement:
ST elevation in aVR
ST elevation in V1 > 2.5 mm
Complete RBBB
ST depression in V5
**Occlusion proximal to D1
Signs of high lateral involvement:
ST elevation / Q-wave formation in aVL
ST depression ≥ 1 mm in II, III or aVF (reciprocal to STE in aVL)(leads I and aVL).