45-year-old male with 1 hour of chest pain radiating to the back.
In a patient with a concerning history of chest pain, the most striking part of this EKG is the ST-segment depression in V2-3—the EKG depiction of an acute isolated posterior MI.
Posterior wall MI usually accompanies an inferior MI, identified as ST-segment depression in V2-4 (often referred to as “reciprocal” changes). Rarely, in maybe 3-5% of all acute MIs, an occlusion of the circumflex artery may cause identifiable infarction in only the posterior wall.
Remember, the posterior wall of the heart has no direct EKG representation—we see “reverse” changes in the EKG as the anterior leads (V2-4) reveal the posterior wall changes. Instead of the ST-elevation of an acute transmural MI of the anterior surface of the heart, these leads will depict ST-segment depression with a posterior wall infarct. Imagine picking the EKG up from the bottom and flipping it over—these same leads now reveal typical ST-segment elevation (a visual aid to help you believe!).
This presentation is important to recognize because it is an appropriate opportunity for acute intervention. These patients should be referred to interventional cardiology for catheterization and angioplasty. If interventional cath is unavailable, thrombolytics should be considered.
Life in the Fast Lane has a particularly good page on this topic.