PR interval

Schematic representation of normal EKG

In electrocardiography, the PR interval is the period, measured in milliseconds, that extends from the beginning of the P wave (the onset of atrial depolarization) until the beginning of the QRS complex (the onset of ventricular depolarization); it is normally between 120 and 200ms in duration. If a Q wave is measured by EKG, the PR interval is sometimes termed the PQ interval.

Interpretation

Variations in the PR interval can be associated with certain medical conditions:

• Duration
  • A long PR interval (of over 200 ms) may indicate a first degree heart block.^[1] Prolongation can be associated with hypokalemia, acute rheumatic fever,^[2] or carditis associated with Lyme disease.^[3]
  • A short PR interval (of less than 120ms) may be associated with Wolff–Parkinson–White syndrome, Lown–Ganong–Levine syndrome, or Junctional rhythms.
  • A variable PR interval may indicate other types of heart block.
• PR segment depression may indicate atrial injury^[4] or pericarditis.^[5]
• Variable morphologies of P waves in a single EKG lead is suggestive of an ectopic pacemaker rhythm such as wandering pacemaker or multifocal atrial tachycardia.

References

1. First-Degree Atrioventricular Block at eMedicine
2. http://www.utmb.edu/pedi_ed/core/cardiology/page_40.htm[]
3. Costello, J. M.; Alexander, M. E.; Greco, K. M.; Perez-Atayde, A. R.; Laussen, P. C. (2009). "Lyme Carditis in Children: Presentation, Predictive Factors, and Clinical Course". Pediatrics 123 (5): e835–41. doi:10.1542/peds.2008-3058. PMID 19403477.
4. Rao, B.N. Vijay Raghawa (2009). "Evolution of ECG Changes". Clinical Examinations in Cardiology. pp. 561–2. ISBN 978-81-312-0964-6.
5. Pedley, D. K.; Brett, C; Nichol, N (2002). "P-R segment depression: An early diagnostic feature in acute pericarditis: A telephone survey of UK accident and emergency departments". European Journal of Emergency Medicine 9 (1): 43–5. PMID 11989495.