II. Definitions

  1. PR Interval
    1. Duration from the START of the P Wave to the start of the QRS Complex
    2. Represents electrical conduction from atrial depolarization to the start of ventricular depolarization
      1. Includes signal conduction through atria, AV Node, common bundle and bundle branches
      2. AV Node conduction is responsible for the majority of the PR Segment duration
  2. PR Segment
    1. Duration from the END of the P Wave to the start of the QRS Complex

III. Findings: Normal

  1. PR Segment is Isoelectric
  2. Normal Interval in Adults: 0.12 to 0.20 s (120 to 200 ms)
  3. Normal interval in Children: 0.07 to 0.18 s (70 to 180 ms)

IV. Causes: Prolonged PR Interval

  1. AV Node Block
  2. Hyperthyroidism (occasional)
  3. Normal variant (rarely)

V. Causes: Shortened PR Interval

  1. Wolf-Parkinson-White Syndrome (WPW Syndrome)
    1. Always look closely for a Delta Wave in Short PR Interval
  2. AV nodal rhythm (Junctional Rhythm)
  3. Low atrial nodal rhythm
  4. Lown-Ganong-Levine (LGL)
  5. Hypertension
  6. Normal variant

VI. Causes: PR Depression

  1. Myocardial Infarction involving atrium
  2. Acute Pericarditis (also with downsloping TP segment)

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