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Revision as of 00:56, 23 August 2013

The PR duration depends on the conduction velocity in the atria, AV node, His bundle, bundle branches and Purkinje fibers.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

The PR interval starts at the beginning of the atrial excitation (beginning of the P wave and ends at the beginning of the ventricular excitation (beginning of the QRS complex. It is termed the PQ interval if a Q wave is present. The PR interval measures the time required for an electrical impulse to travel from the atrial myocardium adjacent to the sinoatrial (SA) node to the ventricular myocardium adjacent to the fibers of the Purkinje network.

The duration of the PR interval is normally from 0.10 to 0.21 s. A major portion of the PR interval reflects the slow conduction of an impulse through the AV node, which is controlled by the balance between the sympathetic and parasympathetic divisions of the autonomic nervous system. Therefore, the PR interval varies with the heart rate, being shorter at faster rates when the sympathetic component predominates, and vice versa. The PR interval tends to increase with age ^[1] ^[2];

In childhood: 0.10 - 0.20 sec
In adolescence: 0.12 - 0.16 sec
In adulthood: 0.14 - 0.21 sec

Changes in PR interval

A prolonged PQ interval is a sign of delayed conduction through the atrium and AV node. Pathophysiologically, this can be due to 1st, 2nd or 3rd degree AV block, increased vagal tone [Bezold-Jarisch reflex; described as an eponym for a triad of responses (apnea, bradycardia, and hypotension) following intravenous injection of veratrum alkaloids in experimental animals], or it can be pharmacologically induced.^[3] ^[4]

A short PR interval can be seen in the WPW syndrome in which a faster connection exists between the atria and the ventricles.

Shortens up to a rate of 140 to 150 beats per minute through a withdrawal of parasympathetic tone ^[5] ^[6].
PR may increase with increasing rate in the presence of digoxin or if the conducting system is diseased.
If the atria are artificially paced the PR increases as the paced rate increases ^[7].
Children have shorter PR intervals (0.11 at 1 year).
Prolongation can be a normal variant: 67.000 healthy airmen studied and 0.52% found to have a prolonged PR.

80% of the PR prolongations ranged from 0.21 to 0.24 ^[8]. In a second study 59 of 19.000 (0.31%) airmen had a PR of 0.24 or more ^[9].

In healthy middle aged men, a prolongation of the PR in the presence of a normal QRS does not affect prognosis and is not related to ischemic heart disease ^[10].
PR prolongation often signifies a delay in the AV node but may reflect intra atrial or His Purkinje disease.

Causes of Short PR Interval

Life Threatening Causes

Life-threatening causes include conditions which result in death or permanent disability within 24 hours if left untreated.

Common Causes

List the most common causes here.

Causes by Organ System

Cardiovascular	Congenital heart disease, congestive heart failure, coronary heart disease, dilated cardiomyopathy, Ebstein’s anomaly, hypertensive heart disease, hypertrophic cardiomyopathy, ischemic heart disease, junctional arrhythmias, Lown-Ganong-Levine syndrome, Mahaim fiber tachycardia, mitral regurgitation, mitral stenosis, mitral valve prolapse, myocardial infarction, myocarditis, obstructive sleep apnea, pericarditis, restrictive cardiomyopathy, rheumatic fever, sustained ventricular tachycardia, valvular heart disease, Wolff-Parkinson-White syndrome
Chemical/Poisoning	No underlying causes
Dental	No underlying causes
Dermatologic	No underlying causes
Drug Side Effect	5-fluorouracil, aminophylline, amiodarone, amlodipine, amphetamines, beta blockers, carbamazepine, cimetidine, clonidine, digoxin, diltiazem, dobutamine, ephedrine, flumazenil, guanethidine, isoproterenol, lithium, methyldopa, phenylephrine, reserpine, salbutamol, sympathomimetic agents, tacrolimus, theophylline, thiazides, verapamil
Ear Nose Throat	No underlying causes
Endocrine	Cushing's syndrome, diabetic ketoacidosis, hypothyroidism, pheochromocytoma, thyrotoxicosis
Environmental	No underlying causes
Gastroenterologic	No underlying causes
Genetic	Duchenne's muscular dystrophy, Emery-Dreifuss muscular dystrophy, Fabry disease, Friedreich ataxia, glycogen storage disease II, hemochromatosis, LQT type 4, Pompe disease
Hematologic	No underlying causes
Iatrogenic	Cardioversion, pacemaker malfunction, permanent pacemaker
Infectious Disease	Chagas disease, diphtheria, leptospirosis, Lyme disease, pneumonia, rheumatic fever, salmonella, trichinosis
Musculoskeletal/Orthopedic	Duchenne's muscular dystrophy, Emery-Dreifuss muscular dystrophy
Neurologic	Friedreich ataxia
Nutritional/Metabolic	Diabetic ketoacidosis, Fabry disease, glycogen storage disease II, hypocalcemia, hypokalemia, hypomagnesemia, Pompe disease
Obstetric/Gynecologic	No underlying causes
Oncologic	No underlying causes
Ophthalmologic	No underlying causes
Overdose/Toxicity	Cannabis, cocaine, digoxin, grayanotoxin
Psychiatric	No underlying causes
Pulmonary	Acute respiratory failure, chronic obstructive pulmonary disease, obstructive sleep apnea, pneumonia, pulmonary embolism
Renal/Electrolyte	Chronic renal failure
Rheumatology/Immunology/Allergy	Scleroderma
Sexual	No underlying causes
Trauma	No underlying causes
Urologic	No underlying causes
Miscellaneous	Idiopathic

Causes in Alphabetical Order

Differential Diagnosis of the Shortened PR Interval:

Differential Diagnosis of a Prolonged PR Interval

Beta blocker therapy
AV block due to coronary artery disease, rheumatic disease
Hyperthyroidism
Normal variant

Differential Diagnosis of the Depressed PR Interval:

Additional resources

References

↑ Beckwith JR. Grant's clinical electrocardiography. New York: McGraw–Hill, 1970:50.
↑ Marriott's Practical Electrocardiography, Wagner G.S., 10th edition, 2001
↑ Aviado DM, Guevara Aviado D. The Bezold-Jarisch reflex: A historical perspective of cardiopulmonary reflexes, Ann N Y Acad Sci. 2001 Jun; 940: 48-58
↑ Mark AL. The Bezold-Jarisch reflex revisited: clinical implications of inhibitory reflexes originating in the heart. J Am Coll Cardiol. 1983 Jan;1 (1): 90-102.
↑ Chou's Electrocardiography in Clinical Practice.
↑ Atterhog, J. Electrocardiol. 1977:10,331.
↑ Lister,J., Am.J. Cardiol 1965:16,516.
↑ Johnson, R, Am. J. Cardiol. 1960:6,153.
↑ Manning, G., Am. J. Cardiol.1962:9,558.
↑ Erikssen, J.,Clin.Card. 1984:7,6.
↑ Marriott's Practical Electrocardiography
↑ Goldberger's Clinical Electrocardiography

Template:WikiDoc Sources

[1] Beckwith JR. Grant's clinical electrocardiography. New York: McGraw–Hill, 1970:50.

[2] Marriott's Practical Electrocardiography, Wagner G.S., 10th edition, 2001

[3] Aviado DM, Guevara Aviado D. The Bezold-Jarisch reflex: A historical perspective of cardiopulmonary reflexes, Ann N Y Acad Sci. 2001 Jun; 940: 48-58

[4] Mark AL. The Bezold-Jarisch reflex revisited: clinical implications of inhibitory reflexes originating in the heart. J Am Coll Cardiol. 1983 Jan;1 (1): 90-102.

[5] Chou's Electrocardiography in Clinical Practice.

[6] Atterhog, J. Electrocardiol. 1977:10,331.

[7] Lister,J., Am.J. Cardiol 1965:16,516.

[8] Johnson, R, Am. J. Cardiol. 1960:6,153.

[9] Manning, G., Am. J. Cardiol.1962:9,558.

[10] Erikssen, J.,Clin.Card. 1984:7,6.

[11] Marriott's Practical Electrocardiography

[12] Goldberger's Clinical Electrocardiography

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@@ Line 38: / Line 38: @@
 {|style="width:80%; height:100px" border="1"
 |style="height:100px"; style="width:25%" border="1" bgcolor="LightSteelBlue" | '''Cardiovascular'''
-|style="height:100px"; style="width:75%" border="1" bgcolor="Beige" | No underlying causes
+|style="height:100px"; style="width:75%" border="1" bgcolor="Beige" | [[Congenital heart disease]],  [[congestive heart failure]],  [[coronary heart disease]],  [[dilated cardiomyopathy]],  [[Ebstein’s anomaly]],  [[hypertensive heart disease]],  [[hypertrophic cardiomyopathy]],  [[ischemic heart disease]],  [[junctional arrhythmias]],  [[Lown-Ganong-Levine syndrome]],  [[Mahaim fiber tachycardia]],  [[mitral regurgitation]],  [[mitral stenosis]],  [[mitral valve prolapse]],  [[myocardial infarction]],  [[myocarditis]],  [[obstructive sleep apnea]],  [[pericarditis]],  [[restrictive cardiomyopathy]],  [[rheumatic fever]],  [[sustained ventricular tachycardia]],  [[valvular heart disease]],  [[Wolff-Parkinson-White syndrome]]
 |-
 |-bgcolor="LightSteelBlue"
@@ Line 54: / Line 54: @@
 |-bgcolor="LightSteelBlue"
 | '''Drug Side Effect'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[5-fluorouracil]],  [[aminophylline]],  [[amiodarone]],  [[amlodipine]],  [[amphetamines]],  [[beta blockers]],  [[carbamazepine]],  [[cimetidine]],  [[clonidine]],  [[digoxin]],  [[diltiazem]],  [[dobutamine]],  [[ephedrine]],  [[flumazenil]],  [[guanethidine]],  [[isoproterenol]],  [[lithium]],  [[methyldopa]],  [[phenylephrine]],  [[reserpine]],  [[salbutamol]],  [[sympathomimetic agents]],  [[tacrolimus]],  [[theophylline]],  [[thiazides]],  [[verapamil]]
 |-
 |-bgcolor="LightSteelBlue"
@@ Line 62: / Line 62: @@
 |-bgcolor="LightSteelBlue"
 | '''Endocrine'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Cushing's syndrome]],  [[diabetic ketoacidosis]],  [[hypothyroidism]],  [[pheochromocytoma]],  [[thyrotoxicosis]]
 |-
 |-bgcolor="LightSteelBlue"
@@ Line 74: / Line 74: @@
 |-bgcolor="LightSteelBlue"
 | '''Genetic'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Duchenne's muscular dystrophy]],  [[Emery-Dreifuss muscular dystrophy]],  [[Fabry disease]],  [[Friedreich ataxia]],  [[glycogen storage disease II]],  [[hemochromatosis]],  [[LQT type 4]],  [[Pompe disease]]
 |-
 |-bgcolor="LightSteelBlue"
@@ Line 82: / Line 82: @@
 |-bgcolor="LightSteelBlue"
 | '''Iatrogenic'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Cardioversion]],  [[pacemaker malfunction]],  [[permanent pacemaker]]
 |-
 |-bgcolor="LightSteelBlue"
 | '''Infectious Disease'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Chagas disease]],  [[diphtheria]],  [[leptospirosis]],  [[Lyme disease]],  [[pneumonia]],  [[rheumatic fever]],  [[salmonella]],  [[trichinosis]]
 |-
 |-bgcolor="LightSteelBlue"
 | '''Musculoskeletal/Orthopedic'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Duchenne's muscular dystrophy]],  [[Emery-Dreifuss muscular dystrophy]]
 |-
 |-bgcolor="LightSteelBlue"
 | '''Neurologic'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Friedreich ataxia]]
 |-
 |-bgcolor="LightSteelBlue"
 | '''Nutritional/Metabolic'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Diabetic ketoacidosis]],  [[Fabry disease]],  [[glycogen storage disease II]],  [[hypocalcemia]],  [[hypokalemia]],  [[hypomagnesemia]],  [[Pompe disease]]
 |-
 |-bgcolor="LightSteelBlue"
@@ Line 114: / Line 114: @@
 |-bgcolor="LightSteelBlue"
 | '''Overdose/Toxicity'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Cannabis]],  [[cocaine]],  [[digoxin]],  [[grayanotoxin]]
 |-
 |-bgcolor="LightSteelBlue"
@@ Line 122: / Line 122: @@
 |-bgcolor="LightSteelBlue"
 | '''Pulmonary'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Acute respiratory failure]],  [[chronic obstructive pulmonary disease]],  [[obstructive sleep apnea]],  [[pneumonia]],  [[pulmonary embolism]]
 |-
 |-bgcolor="LightSteelBlue"
 | '''Renal/Electrolyte'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Chronic renal failure]]
 |-
 |-bgcolor="LightSteelBlue"
 | '''Rheumatology/Immunology/Allergy'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Scleroderma]]
 |-
 |-bgcolor="LightSteelBlue"
@@ Line 146: / Line 146: @@
 |-bgcolor="LightSteelBlue"
 | '''Miscellaneous'''
-|bgcolor="Beige"| No underlying causes
+|bgcolor="Beige"| [[Idiopathic]]
 |-
 |}

v t e Electrocardiography
Overview	History of the EKG • EKG interpretation basics • Normal sinus rhythm
EKG Complexes	P wave • QRS complex • ST Segment • T wave • T wave alternans • Tombstone T wave • U wave Osborn wave • H wave • K wave • Delta wave NSSTW changes
EKG Intervals	PR Interval • QRS Interval • ST Interval • QT Interval
Conduction System & Bradycardia	Cardiac pacemaker • SA node • AV node• Bundle of His • Purkinje fibers • Sinus bradycardia • First Degree AV Block • Second Degree AV Block • Complete or Third-Degree AV Block • Concealed conduction • AV Junctional Rhythms • LBBB • LAHB • LPHB • RBBB • Trifascicular block
Atrial Arrhythmias	Sinus tachycardia • Premature Atrial Contractions (PACs) • Ectopic Atrial Rhythm • Paroxysmal Atrial Tachycardia (PAT) • Paroxysmal Atrial Tachycardia (PAT) with Block • Multifocal Atrial Tachycardia (MAT) • Atrial Flutter • Atrial Fibrillation • Wandering atrial pacemaker
Ventricular Arrhythmias	Differential Diagnosis of Tachycardia with a Wide QRS Complex • Accelerated Idioventricular Rhythm • Ventricular Parasystole • Premature Ventricular Contractions (PVCs) • Ventricular tachycardia • Ventricular Fibrillation • Sudden cardiac death
EKG Abnormalities in Disease States	Hypertrophy & Dilatation • Right atrial enlargement • Left atrial enlargement • Biatrial enlargement • Left Ventricular Hypertrophy • Right Ventricular Hypertrophy • Biventricular Hypertrophy • Acute myocardial infarction • NSTEMI • STEMI • Tombstone ST elevation • Right ventricular myocardial infarction • Atrial infarction Pre-excitation Syndromes • Wolff-Parkinson-White Syndrome • Lown Ganong Levine Syndrome • Mahaim Type Preexcitation Cardiomyopathies • Arrhythmogenic Right Ventricular Dysplasia • Dilated Cardiomyopathy • Hypertrophic Cardiomyopathy Drug Effects on the EKG • Adenosine • β-blockers • Digitalis • Quinidine • Procainamide • Disopyramide • Lidocaine • Tocainide and Mexiletine • Phenytoin • Encainide, Flecainide and Propafenone • Amiodarone • Bretylium • Ca Channel Blockers • Phenothiazines • Tricyclic Antidepressants • Lithium Congenital Heart Disease • Dextrocardia • Atrial Septal Defect • Ventricular Septal Defect • Tetralogy of Fallot • Conjoined Twins or Siamese Twins • Congenital heart block Electrolyte Disturbances • Hyperkalemia • Hypokalemia • Hypercalcemia • Hypocalcemia • Nonspecific Changes Other Heart Diseases • Pericarditis • Myocarditis • Tamponade • Heart Transplantation • Sick Sinus Syndrome • Long QT Syndrome Inherited Disease • Brugada Syndrome Systemic Diseases • CNS Disease • Cardiac Tumors Heart Transplantation • EKG Changes in patient with Heart Transplantation Exogenous Effects • Hypothermia • Chest Trauma • Insect Bites • Electric Injuries
Technical Issues and Potential Errors in Interpretation	Artifacts • Lead Placement Errors • The EKG in a Patient with a Pacemaker • EKG in athletes