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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Elsaiey, MBBCH [2]

See also: Junctional bradycardia for slow junctional rhythms, and junctional tachycardia for fast jucntional rhythms

Overview

Junctional rhythm describes an abnormal heart rhythm resulting from impulses coming from a locus of tissue in the area of the atrioventricular node, the "junction" between atria and ventricles. Junctional rhythm can be classified into junction escape rhythm, accelerated junctional rhythm, junctional bradycardia, and junctional tachycardia. The junctional rhythm can be originated by many medications that affect the sinoatrial node and make the atrioventricular node an ectopic impulses foci. Many conditions as well causes junctional rhythm by creating new pacemaker instead of the sinoatrial node. In junctional rhythm, the heart beats rate are not controlled by the sinoatrial node. The new pacemaker in the junctional rhythm is the atrioventricular node. Common causes of junctional rhythm include acute MI, Acute rheumatic fever, antiarrhythmic agents, beta-blockers, calcium channel blockers, Complete heart block, Conduction system disease, Digitalis toxicity, Diphtheria, Healthy response during sleep in patients with heightened vagal tone, Heart surgery particularly valve replacement or surgery for congenital heart disease, Ischemic heart disease, Lyme disease, NSTEMI, Sick sinus syndrome, Sinus arrest, Chest trauma, Radiation therapy, Collagen vascular disease, Myocarditis, Clonidine, Reserpine, Adenosine, and Cimetidine. In the United States, the prevalence of junctional rhythm is 166 in 100,000 individuals with sinus node dysfunction. If left untreated, junctional rhythm can lead to syncope and other severe complications. Patients presenting with juncitonal rhythm disease should be asked properly for history of other cardiac conditions as heart failure and sick sinus syndrome. Symptoms of junctional rhythm can be non specific and includes syncope, dizziness, and faitgue. Physical examination findings of junctional rhythm include pulsating veins and canon a waves in case the right atrium contracting against a closed tricuspid valve. Electrocardiogram may show QRS complexes are narrow as conduction down the His bundle is normal. The junctional rate may be slow (40-60 beats per minute) in which case the rhythm is referred to as junctional bradycardia. The junctional rate may be rapid in which case the rhythm is referred to as a junctional tachycardia. Asymptomatic patients with only juncitonal rhythm and no other cardiac conditions do not require further management. The rhythm here is due to increased vagal tone only. Patients with sinus node dysfunction should be managed cautiously as the pulse originating from other foci keeps the heart rate. Patients with junctional rhythm due to digoxin toxicity are given atropine and digoxin specific antibody. In children, symptomatic patients can undergo percutaneous radiofrequency ablation. Pacemaker is indicated for patients with sick sinus syndrome and complete AV block.

Classification

  • Junctional rhythm can be classified according to the rate of the heart rate as the following:[1][2][3]

Junctional Rhythm

  • The junctional rate is normal.

Junction escape rhythm:

  • The junctional rate is about 40-60 beats per minute.

Accelerated junctional rhythm:

  • The juncitonal rate can be accelerated (60-100 beats per minute).

Junctional Bradycardia

  • The junctional rate may be slow (40-60 beats per minute) in which case the rhythm is referred to as junctional bradycardia.

Junctional Tachycardia

Pathophysiology

Physiology

  • The sinoatrial node in the heart is the pacemaker that determine the rate of the heart beats. The electrical impulse starts from the sinoatrial node then travels through the atria. It continues through the bundle of his, Purkinje fibers, and the ventricles ending one heart beat.[4][5]
  • This sinus rhythm indicates the atria normally contracts before the ventricles.

Pathogenesis

  • The junctional rhythm can be originated by many medications that affect the sinoatrial node and make the atrioventricular node an ectopic impulses foci. Many conditions as well causes junctional rhythm by creating new pacemaker instead of the sinoatrial node.[6]
  • In junctional rhythm, the heart beats rate are not controlled by the sinoatrial node. The new pacemaker in the junctional rhythm is the atrioventricular node.[7]
  • The atria contracts before the ventricles but from a different signal. The impulse contracting the atria comes from the ventricles not the normal impulse coming from the sinoatrial node.[8][9]
  • Junctional tacycardia:[10][11]
    • Occurs when the atrioventricular node becomes the pacemaker and spreads impulse in a rapid pattern.
    • It takes place when the myocardial tissue is inflammed and ischemic as in patients undergo a heart surgery.

Causes

Differentiating Junctional Rhythm from other diseases

  • Junctional rhythm must be differentiated from other diseases that cause abnormal cardiac electrical conduction.


Arrhythmia Rhythm Rate P wave PR Interval QRS Complex Response to Maneuvers Epidemiology Co-existing Conditions
Junctional rhythm[13][12]
  • Regular
  • 40 - 60
  • Normal
  • Prevalence: 166 in 100,000 individuals with sinus node dysfunction in the united.
Atrioventricular block[14] First degree [15][16]
  • Regular
  • Normal
  • Prolonged PR interval (>200 msec)
  • Less than 0.12 seconds, consistent, and normal in morphology.
  • No treatment required


  • Prevalence: 650 to 1600 per 100,000 individuals in the united states.

Second degree[17][18]
  • Regular irregular
  • Normal
  • Mobtiz I: Progressive PR prolongation
  • Mobitz II: Normal PR interval
QRS is normal but dropped as the following:
  • Mobitz I: QRS complex is dropped after a progressive lengthening of PR
  • Mobitz II: QRS complex is dropped after a normal PR
  • Can be reversed by using a pacemaker.
  • Prevalence: 3 per 100,000 individuals in the united states.
Third degree[19][20]
  • Regular
  • Normal but no relationship between P wave and the QRS.
  • More P waves than the QRS complexes.
  • Varies
  • Normal QRS
  • Can be reversed by using a pacemaker.
  • The prevalence: 20 per 100,000 individuals worldwide.
Atrial Fibrillation (AFib)[21][22]
  • Irregularly irregular
  • Absent
  • Fibrillatory waves
  • Absent
  • Less than 0.12 seconds, consistent, and normal in morphology in the absence of aberrant conduction
  • 2.7–6.1 million people in the United States have AFib
  • 2% of people younger than age 65 have AFib, while about 9% of people aged 65 years or older have AFib
Atrial Flutter[23]
  • Regular or Irregular
  • 75 (4:1 block), 100 (3:1 block) and 150 (2:1 block) beats per minute (bpm), but 150 is more common
  • Sawtooth pattern of P waves at 250 to 350 bpm
  • Biphasic deflection in V1
  • Varies depending upon the magnitude of the block, but is short
  • Less than 0.12 seconds, consistent, and normal in morphology
  • Conduction may vary in response to drugs and maneuvers dropping the rate from 150 to 100 or to 75 bpm
Atrioventricular nodal reentry tachycardia (AVNRT)[24][25][26][27]
  • Regular
  • 140-280 bpm
  • Slow-Fast AVNRT:
    • Pseudo-S wave in leads II, III, and AVF
    • Pseudo-R' in lead V1.
  • Fast-Slow AVNRT
  • Slow-Slow AVNRT
  • Inverted, superimposed on or buried within the QRS complex (pseudo R prime in V1/pseudo S wave in inferior leads)
  • Absent (P wave can appear after the QRS complex and before the T wave, and in atypical AVNRT, the P wave can appear just before the QRS complex)
  • Less than 0.12 seconds, consistent, and normal in morphology in the absence of aberrant conduction
  • QRS alternans may be present
Multifocal Atrial Tachycardia[28][29]
  • Irregular
  • Atrial rate is > 100 beats per minute
  • Varying morphology from at least three different foci
  • Absence of one dominant atrial pacemaker, can be mistaken for atrial fibrillation if the P waves are of low amplitude
  • Less than 0.12 seconds, consistent, and normal in morphology
Paroxysmal Supraventricular Tachycardia
  • Regular
  • 150 and 240 bpm
  • Absent
  • Hidden in QRS
  • Absent
  • Narrow complexes (< 0.12 s)
Premature Atrial Contractrions (PAC)[30][31]
  • Regular except when disturbed by premature beat(s)
  • 80-120 bpm
  • Upright
  • > 0.12 second
  • May be shorter than that in normal sinus rhythm (NSR) if the origin of PAC is located closer to the AV node
  • Ashman’s Phenomenon:
  • Usually narrow (< 0.12 s)
Wolff-Parkinson-White Syndrome[32][33]
  • Regular
  • Atrial rate is nearly 300 bpm and ventricular rate is at 150 bpm
  • Less than 0.12 seconds
  • A delta wave and evidence of ventricular pre-excitation if there is conduction to the ventricle via ante-grade conduction down an accessory pathway
  • A delta wave and pre-excitation may not be present because bypass tracts do not conduct ante-grade.

Epidemiology and Demographics

Prevalence

  • In the United States, the prevalence of junctional rhythm is 166 in 100,000 individuals with sinus node dysfunction.[13]

Age

  • The prevalence of junctional rhythm increases with age.

Gender

  • Men and women are affected equally by juntional rhythm.

Natural History, Complications and Prognosis

Natural History

  • If left untreated, junctional rhythm can lead to syncope and other severe complications.[34]

Complications

  • Complications of junctional rhythm include the following:[34]
    • Syncope
    • Dizziness
    • Fatigue

Prognosis

  • Prognosis of junctional rhythm is good with the proper treatment.

History and Symptoms

History

  • Patients presenting with juncitonal rhythm disease should be asked properly for history of other cardiac conditions.
  • Other cardiac conditions can affect the presentation of the patients. These cardiac conditions include:
    • Heart failure
    • Sick sinus syndrome

Symptoms

  • Patients with juncitonal rhythm disease can be asymptomatic.
  • Symptoms of junctional rhythm can be non specific and includes the following:
    • Dizziness
    • Fatigue
    • Syncope
    • Palpitaions
  • Symptoms vary according to the underlying cause of junctional rhythm as the following:[35][36][37]
    • Heart failure:
      • Shortness of breath
      • Lower extremities edema
    • Valve dysfunction due to rheumatic fever:
      • Fever
      • Arthritis
      • Skin rash

Physical Examination

  • Common physical examination findings of junctional rhythm include the following:
    • Pulsating veins
    • Canon a waves in case the right atrium contracting against a closed tricuspid valve
    • Regular heart rate in most of cases ranging from 40 to 60 beat per minute

Diagnosis

Electrocardiogram

  • The QRS complexes are narrow in so far as conduction down the His bundle is normal
  • The junctional rate may be slow (40-60 beats per minute) in which case the rhythm is referred to as junctional bradycardia
  • The junctional rate may be normal as shown in the tracing below
  • The junctional rate may be rapid in which case the rhythm is referred to as a junctional tachycardia
  • There is dissociation of the narrow complex QRS from an upright atrial p wave or the p wave is missing, or the p wave is retrograde (a retrograde p wave) due to retrograde conduction from the AV node back into the atrium.

EKG Examples


Shown below is an EKG depicting AV dissociation with variable timing of the p wave in relation to the QRS. A narrow complex junctional escape rhythm at 75 beats per minute is present.


Shown below is an EKG with a a regular rhythm at a rate of about 43/minute. There are no P waves to be seen and the QRS duration is about 80 ms. This is a nodal rhythm.

Copyleft images obtained courtesy of ECGpedia, http://en.ecgpedia.org.

Treatment

Medical therapy

  • The underlying cause of junctional rhythm should be defined first before attempting treatment.
  • Asymptomatic patients with only juncitonal rhythm and no other cardiac conditions do not require further management. The rhythm here is due to increased vagal tone only.
  • Patients with sinus node dysfunction should be managed cautiously as the pulse originating from other foci keeps the heart rate.
  • Patients with junctional rhythm due to digoxin toxicity are given atropine and digoxin specific antibody.[38][39]
  • Patients who do not respond to the usual medical therapy can be administered phenytoin.

Surgery

  • In children, symptomatic patients can undergo percutaneous radiofrequency ablation. [40]
  • Pacemaker:[41]
    • Indicated for patients with sick sinus syndrome and complete AV block.

Related Chapters

References

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