II. Definitions
- ST Segment
- Duration from the end of the QRS Complex (S Wave) to the end of the T Wave
- Represents a pause in electrical conduction while awaiting ventricular repolarization after depolarization
III. Causes: ST Elevation
IV. Causes: ST Depression
- See aVR ST Elevation with Diffuse ST Depression
- Myocardial Ischemia (horizontal or downsloping ST depression)
- Right Ventricular Myocardial Infarction (ST depression in precordial leads)
- Associated with ST Elevation in v4R adjunctive ekg lead
- Posterior Myocardial Infarction (ST depression in precordial leads)
- Associated with ST Elevation in V8 or V9 adjunctive ekg leads placed below left Scapula
- Left Ventricular Hypertrophy or Right Ventricular Hypertrophy (repolarization changes)
-
Bundle Branch Block (repolarization changes)
- ST Segment change direction is typically discordant or opposite QRS Complex direction (See Sgarbossa Criteria)
- Central Nervous System Disorder
- Mitral Valve Prolapse
- Acute Pancreatitis (non-specific ST Segment abnormalities)
-
Electrolyte and Metabolic Conditions
- Hypokalemia
- Myxedema or Severe Hypothyroidism (non-specific ST Segment abnormalities)
- Bradycardia and flat or inverted T Waves are more common
- Medication Adverse Effects
- Digitalis Toxicity (sagging or scooped out ST Segment)
- Antiarrhythmic agent
V. References
- Keefe (2008) Complete Guide to EKGs, Jones and Bartlett, Sudbury, p. 18-9