Long PR interval

(Redirected from Prolonged PR interval)
Jump to navigation Jump to search

WikiDoc Resources for Long PR interval


Most recent articles on Long PR interval

Most cited articles on Long PR interval

Review articles on Long PR interval

Articles on Long PR interval in N Eng J Med, Lancet, BMJ


Powerpoint slides on Long PR interval

Images of Long PR interval

Photos of Long PR interval

Podcasts & MP3s on Long PR interval

Videos on Long PR interval

Evidence Based Medicine

Cochrane Collaboration on Long PR interval

Bandolier on Long PR interval

TRIP on Long PR interval

Clinical Trials

Ongoing Trials on Long PR interval at Clinical Trials.gov

Trial results on Long PR interval

Clinical Trials on Long PR interval at Google

Guidelines / Policies / Govt

US National Guidelines Clearinghouse on Long PR interval

NICE Guidance on Long PR interval


FDA on Long PR interval

CDC on Long PR interval


Books on Long PR interval


Long PR interval in the news

Be alerted to news on Long PR interval

News trends on Long PR interval


Blogs on Long PR interval


Definitions of Long PR interval

Patient Resources / Community

Patient resources on Long PR interval

Discussion groups on Long PR interval

Patient Handouts on Long PR interval

Directions to Hospitals Treating Long PR interval

Risk calculators and risk factors for Long PR interval

Healthcare Provider Resources

Symptoms of Long PR interval

Causes & Risk Factors for Long PR interval

Diagnostic studies for Long PR interval

Treatment of Long PR interval

Continuing Medical Education (CME)

CME Programs on Long PR interval


Long PR interval en Espanol

Long PR interval en Francais


Long PR interval in the Marketplace

Patents on Long PR interval

Experimental / Informatics

List of terms related to Long PR interval

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: Long PR, long P-R, prolonged PR, prolonged P-R, prolonged PR interval, prolonged P-R interval, PR prolongation, P-R prolongation, PR interval lengthened, P-R interval lengthened


Long PR interval is prolongation of the time required by impulse generated at the normal atrial pacemaker (SA node) to conduct via the normal conduction pathway and activate the ventricle. Normally the conduction time is 0.12 to 0.21 seconds (normal PR interval). A PR interval above 0.21 seconds is called as long PR interval. PR interval is usually longer when the conduction of atrial impulse through AV node is slowed either as a consequence of withdrawal of sympathetic tone or due to an increase in vagal inputs. It is also important to emphasize that long PR intervals can exist in subjects who are otherwise normal.[1] In atrioventricular dissociation where both atria and ventricle beat independently without conducting each others impulse either antegradely or retrogradely, PR interval may vary from beat to beat. In some beats, the PR interval may be long.


First Degree AV Block

First degree AV block may be due to conduction delay in the AV node, His-Purkinje system (made up by the bundle of His and the Purkinje fibers), or a combination of the two. The majority of cases are due to a dysfunction of the AV node; however, when first degree heart block coexists with a bundle-branch block, the cause is more likely to be a conduction delay in the His-Purkinje system. Although there are no missed beats in first degree AV block with all impulses from atria being transmitted to ventricle and thus resulting in a regular ventricular beat rhythm, the conduction delay involving AV node alone typically causes a long PR interval. If the conduction delay also involves the His-Purkinje system, the long PR interval will be associated with wide QRS complex.

Mobitz Type I Second Degree AV Block

The classic site of block in Mobitz type I second degree block is the AV node (70%-75%). In the remaining 25%-30% of the cases the site is infra-nodal (His bundle, bundle branches or fascicles). Mobitz type I is composed of two variations, classic and atypical, based on periodicity. Classic variety usually occurs within the AV node. There is a gradually increasing PR interval and eventually a dropped beat. It is also accompanied by a gradually decreasing R-R interval. The PR interval is usually shortest in the initial beat and gradually increases the ending in a dropped beat and the cycle repeats. This classic Wenckebach phenomenon occurs usually with ratios of 3:2, 4:3 or 5:4. This results in grouped beating. In Atypical variant of Wenckebach pattern the conduction ratios usually exceed 6:5 or 7:6 and the last few beats of the cycle, before a dropped beat, show a relatively constant PR interval (maximum variation of 0.02 sec among them). The beats after the dropped beat again show gradually prolonging PR intervals.[2]

Atrial Premature Beats

In atrial premature beats, also known as atrial premature contractions or premature atrial contractions, with increasing prematurity, the partial penetration of the premature beat (concealed) prolongs the refractory period of the AV node and causes prolongation of the PR interval of the next sinus beat. The PR interval progressively increases until the effective refractory period of AV node is reached, when the atrial premature beats get blocked within the node and non-conducted.[3]

Pseudo-Long 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 long. Although this may appear to be a sinus rhythm with a long PR interval, there is no true impulse conduction between the atrium and ventricle, and hence the name "pseudo long PR interval".[4][5]

Trifascicular Block

On ECG, trifascicular block may manifest with a long PR interval. Trifascicular block involves conduction delay in the right bundle branch plus delay in the main left bundle branch or in both the left anterior and the left posterior fascicles. The diagnosis of trifascicular block requires an electrocardiographic pattern of bifascicular block plus evidence of prolonged conduction below the AV node. This below the AV node conduction delay is most specifically observed as a prolongation of the His-ventricular (HV) time in intracardiac recordings. PR interval includes conduction time in both AV node as well as in the intraventricular conduction system. Prolonged intraventricular conduction may be insufficient to extend the PR interval beyond normal limits, thus a prolonged PR interval can reflect delay in the AV node rather than in all three intraventricular fascicles. So the finding of a long PR interval in the presence of an electrocardiographic pattern consistent with bifascicular block is not diagnostic of trifascicular block, whereas the presence of a normal PR interval does not exclude this finding either. Thus long PR interval is only a concomitant finding in trifascicular block.


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 Based on Pathophysiologic Origin

First Degree AV Block and Mobitz Type I Second Degree AV Block

Atrial Premature Beats

Atrioventricular Dissociation


  1. PACKARD JM, GRAETTINGER JS, GRAYBIEL A (1954). "Analysis of the electrocardiograms obtained from 1000 young healthy aviators; ten year follow-up". Circulation. 10 (3): 384–400. PMID 13190611. Unknown parameter |month= ignored (help)
  2. El-Sherif N, Aranda J, Befeler B, Lazzara R (1978). "Atypical Wenckebach periodicity simulating Mobitz II AV block". Br Heart J. 40 (12): 1376–83. PMC 483582. PMID 737095. Unknown parameter |month= ignored (help)
  3. Damato AN, Lau SH (1971). "Concealed and supernormal atrioventricular conduction". Circulation. 43 (6): 967–70. PMID 4102931. Unknown parameter |month= ignored (help)
  4. Levy MN, Edflstein J (1970). "The mechanism of synchronization in isorhythmic A-V dissociation. II. Clinical studies". Circulation. 42 (4): 689–99. PMID 11993309. Unknown parameter |month= ignored (help)
  5. MILLER R, SHARRETT RH (1957). "Interference dissociation". Circulation. 16 (5): 803–29. PMID 13473052. Unknown parameter |month= ignored (help)

Template:WH Template:WS