PR interval

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. The PR interval is sometimes termed the PQ interval.

Schematic representation of normal EKG

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 an atrioventricular reentrant tachycardia (such as Wolff–Parkinson–White syndrome or Lown–Ganong–Levine syndrome) 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]
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

First-Degree Atrioventricular Block at eMedicine
Karacan M, Ceviz N, Olgun H (2012). "Heart rate variability in children with acute rheumatic fever". Cardiol Young. 22 (3): 285–92. doi:10.1017/S1047951111001429. PMID 21933462.
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.
Rao, B.N. Vijay Raghawa (2009). "Evolution of ECG Changes". Clinical Examinations in Cardiology. pp. 561–2. ISBN 978-81-312-0964-6.
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. doi:10.1097/00063110-200203000-00010. PMID 11989495.

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[1] First-Degree Atrioventricular Block at eMedicine

[pmid21933462-2] Karacan M, Ceviz N, Olgun H (2012). "Heart rate variability in children with acute rheumatic fever". Cardiol Young. 22 (3): 285–92. doi:10.1017/S1047951111001429. PMID 21933462.

[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. doi:10.1097/00063110-200203000-00010. PMID 11989495.