Exam

ST Segment

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ST Segment, ST segment Depression, EKG ST Segment Finding

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