The ST segment
Let’s talk about the ST segment.
ST segment normally represents the interval between the end of ventricular depolarization and beginning of ventricular repolarization.
Normal ST segment
✅ Usually isolectric or may vary from 0.5 mm below to 1 mm above isolectric line in limb leads.
ST segment elevation (STE)
ST changes suggesting myocardial injury:
✅ New STE ≥1 mm in all leads other than V2 or V3.
✅ New STE in V2-V3 ≥2 mm in men older than 40 years old and ≥2.5 mm in men younger than 40 years old or ≥1.5 mm in women.
Types of ST segment elevation include:
✅ Convex Upward
✅ Horizontal
✅ Concave Upward
✅ Obliquely Straight
ST segment elevation - convex upward
ST segment elevation - horizontal
ST segment elevation - concave upward
ST segment elevation - obliquely straight
ST segment depression (STD).
ST changes suggesting myocardial ischemia in the absence of LVH and bundle branch block:
✅ New STD ≥0.5 mm in two contiguous leads and/or T inversion >1 mm in two contiguous leads with R/S ratio >1.
Types of ST segment depression include:
✅ Horizontal
✅ Downsloping
✅ Upsloping
ST segment depression - horizontal
ST segment depression - downsloping
ST segment depression - upsloping
Causes of STD: MI, myocardial ichemia, LVH, bundle branch block, CNS disorder, ventricular aneurysm, electrolyte disturbance, myocarditis, WPW, others.
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