Posterior infarction accompanies 15-20% of STEMIs, usually occurring in the context of an inferior or lateral infarction
Usually caused by posterior descending artery (PDA) occlusion.
Approximately 70% of the population is “right-dominant” (RCA supplies the PDA), while 10% are “left-dominant (the LCx supplies the PDA), and 20% are “co-dominant” (both the RCA and LCx jointly supply the PDA).
Rupture of a coronary artery plaque, thrombosis, and blockage of the downstream perfusion leading to myocardial ischemia and necrosis.
Posterior myocardium is not directly visualised by 12-lead ECG, given the placement of anteroseptal leads V1-V3, they are indirectly examining the posterior wall too
Posterior leads: Posterior MI is confirmed by the presence of ST elevation in the posterior leads (V7-9). The degree of ST elevation seen in V7-9 is typically modest – only 0.5 mm of ST elevation is required to make the diagnosis of posterior MI!
Picture 1 Posterior leads
Lead V7: posterior axillary line
Lead V8: midscapular
Lead V9: paraspinal
ECG 1 STEMI of posterior wall (ST depressions and upright T waves in V1-V3)
ECG 2 STEMI of posterior and inferior wall (ST depressions in V1-V3, STE in II, III, aVF)