ST segment

Definition

The portion of the ECG from the end of the QRS complex (the J point) to the beginning of the T wave, corresponding to the plateau phase of the ventricular action potential, when the ventricular cells sit at about the same voltage. It is normally level with the PR segment and the TP baseline, and deviation is measured at the J point (in some settings, such as exercise testing, 40 to 80 ms after it). Per the 2009 AHA/ACCF/HRS standards (Part VI), J-point elevation of at least 0.1 mV (1 mm) in two contiguous leads is abnormal in every lead except V2 to V3 (which use higher, sex- and age-specific thresholds), and J-point depression is abnormal at 0.05 mV (0.5 mm) or more in V2 to V3 and 0.1 mV (1 mm) or more in all other leads. The Fourth Universal Definition of MI counts new horizontal or downsloping ST 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.

Clinical noteV2 to V3 use higher cut-points: women >=0.15 mV (1.5 mm), men >=40 yr >=0.2 mV (2 mm), men <40 yr >=0.25 mV (2.5 mm).