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

↑ First-Degree Atrioventricular Block at eMedicine
↑ utmb.edu http://www.utmb.edu/pedi_ed/core/cardiology/page_40.htm. Missing or empty |title= (help)
↑ 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. PMID 11989495.

Physiology of the cardiovascular system

Heart

Cardiac output	Cardiac cycle Cardiac output Heart rate Stroke volume Stroke volume End-diastolic volume End-systolic volume Afterload Preload Frank–Starling law of the heart Cardiac function curve Venous return curve Wiggers diagram Pressure volume diagram

Ultrasound	Fractional shortening = (End-diastolic dimension End-systolic dimension) / End-diastolic dimension Aortic valve area calculation Ejection fraction Cardiac index

Heart rate	Cardiac pacemaker Chronotropic (Heart rate) Dromotropic (Conduction velocity) Inotropic (Contractility) Bathmotropic (Excitability) Lusitropic (Relaxation)

Conduction	Conduction system Cardiac electrophysiology Action potential cardiac atrial ventricular Effective refractory period Pacemaker potential Electrocardiography P wave PR interval QRS complex QT interval ST segment T wave U wave Hexaxial reference system

Chamber pressure	Central venous Right atrial ventricular pulmonary artery wedge Left atrial ventricular Aortic

Other	Ventricular remodeling

Vascular system/
Hemodynamics

Blood flow	Compliance Vascular resistance Pulse Perfusion

Blood pressure	Pulse pressure Systolic Diastolic Mean arterial pressure Jugular venous pressure Portal venous pressure

Regulation of BP	Baroreflex Kinin–kallikrein system Renin–angiotensin system Vasoconstrictors Vasodilators Autoregulation Myogenic mechanism Tubuloglomerular feedback Cerebral autoregulation Paraganglia Aortic body Carotid body Glomus cell

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