PR interval - wikipedia 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. 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. Prolongation can be associated with hypokalemia, acute rheumatic fever, or carditis associated with Lyme disease. 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 or pericarditis. 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 Jump up ^ First - Degree Atrioventricular Block at eMedicine Jump up ^ 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. Jump up ^ 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. Jump up ^ Rao, B.N. Vijay Raghawa ( 2009 ). `` Evolution of ECG Changes ''. Clinical Examinations in Cardiology. pp. 561 -- 2. ISBN 978 - 81 - 312 - 0964 - 6. Jump up ^ 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 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 Retrieved from `` https://en.wikipedia.org/w/index.php?title=PR_interval&oldid=804207353 '' Categories : Cardiac electrophysiology Hidden categories : All articles with unsourced statements Articles with unsourced statements from May 2015 Talk About Wikipedia Italiano Polski Українська Edit links This page was last edited on 7 October 2017, at 13 : 49 ( UTC ). About Wikipedia

Question: what is the significance of the pq interval
Answer: 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)