Short PR interval

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vendhan Ramanujam M.B.B.S [2]

Synonyms and Keywords: Shortened PR interval

Overview

A short PR interval is a term in cardiology that connotes a shortened time for the pacemaker in the atrium to conduct an impulse and activate the ventricle (the larger pumping chamber of the heart). While it normally takes 0.12 to 0.21 seconds for the impulse to pass from the atrium to the ventricle (the normal PR interval), a short PR interval is defined as a PR interval of less than 0.12 seconds. Although a short PR interval may be a normal variant, it is also associated with the presence of an accessory bypass tract (e.g. WPW syndrome and LGL syndrome), and close proximity of the atrial impulse to the AV node such as occurs in a premature atrial beat. In AV dissociation, the atrial impulse does not conduct to the ventricle, but the atrium and the ventricle may separately beat at similar rates and the PR interval may vary from beat to beat. In some beats, the PR interval may be quite short.

Pathophysiology

Atrial Premature Beats

Atrial premature beats, also known as atrial premature contractions or premature atrial contractions may emanate from an impulse that originates low in the atrium in close proximity to the AV node which may shorten the time for the impulse to be conducted. Premature atrial beats which arise close to the AV node (low atrial ectopics) may activate the atria in a retrograde fashion which produces an inverted P wave with a relatively short PR interval.

Bypass Tracts

The two subsets of preexcitation syndrome, Lown-Ganong-Levine syndrome and Wolff-Parkinson-White syndrome are associated with short PR interval due to bypass tracts that bypass the AV node, directly connecting the atria with the ventricle.

  • The possible underlying pathophysiology for short PR interval in LGL syndrome can be either faster AV nodal conduction due to the rapidly conducting fibers within the AV node, or rapid conduction through Brechenmacher fibers that bypass the AV node connecting the atria with the bundle of His or the conduction through the accessory pathway James fibers that connect atria with low AV node.
  • Short PR interval in WPW syndrome results from an accessory pathway, the bundle of Kent, that directly connects the atria to the ventricles bypassing the AV node.
  • The difference between WPW and LGL syndrome is that LGL syndrome has a normal QRS complex following ventricular activation via the normal conduction pathway and WPW syndrome has a wide QRS complex due to the combined early ventricular activation via the abnormal accessory pathway and terminal ventricular activation via the normal conduction system.

Junctional Rhythms

In AV junctional rhythms with retrograde atrial activation the retrograde P waves occur before the QRS complex shortening the PR interval. Negative P waves in leads II, III and aVF point towards this diagnosis.

Pseudo-Short PR Interval in Atrioventricular Dissociation

In Atrioventricular dissociation, the atrial impulse does not conduct to the ventricle, but the atrium and the ventricle may separately beat at similar or different rates and the PR interval may vary from beat to beat. In some beats, the PR interval may be quite short. Although this may appear to be a sinus rhythm with a short PR interval, there is no true impulse conduction between the atrium and ventricle, and hence the name "pseudo short PR interval".

Causes

Life Threatening Causes

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

Common Causes

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, isorhythmic A-V dissociation, junctional rhythms, Lown-Ganong-Levine syndrome, Mahaim fiber tachycardia, mitral regurgitation, mitral stenosis, mitral valve prolapse, myocardial infarction, myocarditis, obstructive sleep apnea, pericarditis, preexcitation syndrome, premature atrial beats, 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, salmonellosis, trichinosis
Musculoskeletal/Orthopedic Duchenne's muscular dystrophy, Emery-Dreifuss muscular dystrophy
Neurologic Friedreich ataxia
Nutritional/Metabolic Diabetic ketoacidosis, Fabry disease, glycogen storage disease type 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

References

  1. Perloff JK (1984). "Cardiac rhythm and conduction in Duchenne's muscular dystrophy: a prospective study of 20 patients". Journal of the American College of Cardiology. 3 (5): 1263–8. PMID 6707378. Unknown parameter |month= ignored (help)
  2. Efthimiou J, McLelland J, Betteridge DJ (1986). "Short PR intervals and tachyarrhythmias in Fabry's disease". Postgraduate Medical Journal. 62 (726): 285–7. PMC 2418650. PMID 3086855. Unknown parameter |month= ignored (help)
  3. Huang SK, Rosenberg MJ, Denes P (1984). "Short PR interval and narrow QRS complex associated with pheochromocytoma: electrophysiologic observations". Journal of the American College of Cardiology. 3 (3): 872–5. PMID 6693659. Unknown parameter |month= ignored (help)
  4. Castellanos A, Castillo CA, Agha AS, Tessler M (1971). "His bundle electrograms in patients with short P-R intervals, narrow QRS complexes, and paroxysmal tachycardias". Circulation. 43 (5): 667–78. PMID 5578843. Unknown parameter |month= ignored (help)



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