PR interval explained

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 200 ms in duration.The PR interval is sometimes termed the PQ interval.

Interpretation

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

• Duration
  • A long PR interval (of over 200 ms) indicates a slowing of conduction between the atria and ventricles, usually due to slow conduction through the atrioventricular node (AV node).^[1] This is known as first degree heart block. Prolongation can be associated with fibrosis of the AV node, high vagal tone, medications that slow the AV node such as beta-blockers, hypokalemia, acute rheumatic fever, or carditis associated with Lyme disease.^{[2] [3]}
  • A short PR interval (of less than 120ms) may be associated with a Pre-excitation syndromes such as Wolff–Parkinson–White syndrome or Lown–Ganong–Levine syndrome, and also junctional arrhythmia like atrioventricular reentrant tachycardia or junctional rhythm.
  • A variable PR interval may indicate other types of heart block.
• PR segment depression may indicate atrial injury^[4] or pericarditis.^[5]

See also

• P wave

Notes and References

1. Book: Clinical cardiac electrophysiology in clinical practice. Huang, David T.,, Prinzi, Travis. 978-1-4471-5433-4. Berlin. 897466910. December 2014.
2. Karacan M, Ceviz N, Olgun H . Heart rate variability in children with acute rheumatic fever . Cardiol Young . 22 . 3 . 285–92 . 2012 . 21933462 . 10.1017/S1047951111001429 . 25845504 .
3. 10.1542/peds.2008-3058 . 19403477 . Lyme Carditis in Children: Presentation, Predictive Factors, and Clinical Course . Pediatrics . 123 . 5 . e835–41 . 2009 . Costello . J. M. . Alexander . M. E. . Greco . K. M. . Perez-Atayde . A. R. . Laussen . P. C. . 25270378 .
4. Book: B.N. Vijay Raghawa . Rao . 2009 . Evolution of ECG Changes . https://books.google.com/books?id=_IGGF2Etes8C&pg=PT575 . 561–2 . Clinical Examinations in Cardiology . 978-81-312-0964-6.
5. 11989495 . 2002 . Pedley . D. K. . 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 . Brett . C . Nichol . N . 10.1097/00063110-200203000-00010. 22919251 .