In an inferior MI, the ST segment elevation is approximately how many millimeters?

• A. 5.0 mm
• B. 3.0 mm
• C. 4.0 mm
• D. 6.0 mm

Answer: (A)

ST-segment elevation reflects transmural heart muscle injury. In an inferior myocardial infarction, the abnormal ST elevation appears in the inferior leads (the limb leads II, III, and aVF). The amount of elevation seen in these leads is typically modest—around 1 to 2 millimeters. The STEMI diagnostic criterion for limb leads is at least 1 mm of elevation, so 1–2 mm in the inferior leads is commonly enough to indicate a STEMI in this territory. Larger elevations can occur with bigger infarcts or additional involvement, but 5 mm is not the usual magnitude for an inferior MI. In practice, if the inferior leads show about 1–2 mm of ST elevation along with clinical chest pain, that supports the diagnosis of an inferior STEMI.