ST depression

Definition

Downward displacement of the ST segment below the isoelectric baseline, usually measured at the J point. It can reflect subendocardial ischemia or be a reciprocal change to ST elevation in leads facing the opposite direction, but it also has many nonischemic causes, including ventricular hypertrophy, bundle branch block and other ventricular conduction disturbances, ventricular pacing, digoxin and other drugs, and hypokalemia. The 2009 AHA/ACCF/HRS statement (Part VI) treats J-point depression of at least 0.05 mV (0.5 mm) in V2 and V3 and at least 0.1 mV (1 mm) in the other leads as abnormal, and the Fourth Universal Definition of MI counts new horizontal or downsloping depression of at least 0.05 mV (0.5 mm) in two contiguous leads as an ischemic change. EKGLab's ST Map and ST quizzes flag ST depression at 0.1 mV (1 mm) in every lead. Horizontal depression strongly suggests ischemia, whereas downsloping depression is less specific because it also occurs with left ventricular hypertrophy and in patients taking digoxin.