Junctional rhythm: Difference between revisions

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=== Physiology ===
=== 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.<ref>[http://www.merriam-webster.com/medical/junctional%20rhythm Merriam-Webster dictionary > Junctional rhythm] Retrieved September 2010</ref>
* 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.<ref>[http://www.merriam-webster.com/medical/junctional%20rhythm Merriam-Webster dictionary > Junctional rhythm] Retrieved September 2010</ref><ref name="pmid20797495">{{cite journal| author=Kim D, Shinohara T, Joung B, Maruyama M, Choi EK, On YK | display-authors=etal| title=Calcium dynamics and the mechanisms of atrioventricular junctional rhythm. | journal=J Am Coll Cardiol | year= 2010 | volume= 56 | issue= 10 | pages= 805-12 | pmid=20797495 | doi=10.1016/j.jacc.2010.03.070 | pmc=3050609 | url=https://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=20797495  }}</ref>
*This sinus rhythm indicates the atria normally contracts before the ventricles.
*  
*  


 
=== Pathogenesis ===
Under normal conditions, the heart's [[sinoatrial node]] determines the rate by which the organ beats - in other words, it is the heart's "pacemaker." The electrical activity of [[sinus rhythm]] originates in the sinoatrial node and depolarizes the atria. Current then passes from the atria through the [[bundle of His]], from which it travels along [[Purkinje fibers]] to reach and depolarize the ventricles. This sinus rhythm is important because it ensures that the heart's atria reliably contract before the ventricles.
 
In junctional rhythm, however, the sinoatrial node does not control the heart's rhythm - this can happen in the case of a block in conduction somewhere along the pathway described above. When this happens, the heart's [[atrioventricular node]] takes over as the pacemaker.<ref> eMedicine:"Junctional Rhythms" http://www.emedicine.com/MED/topic1212.htm </ref>. In the case of a junctional rhythm, the atria will actually still contract before the ventricles; however, this does not happen by the normal pathway and instead is due to retrograde conduction (conduction comes from the ventricles or from the AV node into and through the atria).<ref> medical dictionary http://medical-dictionary.thefreedictionary.com/retrograde+conduction</ref>.
In junctional rhythm, however, the sinoatrial node does not control the heart's rhythm - this can happen in the case of a block in conduction somewhere along the pathway described above. When this happens, the heart's [[atrioventricular node]] takes over as the pacemaker.<ref> eMedicine:"Junctional Rhythms" http://www.emedicine.com/MED/topic1212.htm </ref>. In the case of a junctional rhythm, the atria will actually still contract before the ventricles; however, this does not happen by the normal pathway and instead is due to retrograde conduction (conduction comes from the ventricles or from the AV node into and through the atria).<ref> medical dictionary http://medical-dictionary.thefreedictionary.com/retrograde+conduction</ref>.



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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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.

Classification

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 Rhythm

  • The junctional rate is normal

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.[1][2]
  • This sinus rhythm indicates the atria normally contracts before the ventricles.

Pathogenesis

In junctional rhythm, however, the sinoatrial node does not control the heart's rhythm - this can happen in the case of a block in conduction somewhere along the pathway described above. When this happens, the heart's atrioventricular node takes over as the pacemaker.[3]. In the case of a junctional rhythm, the atria will actually still contract before the ventricles; however, this does not happen by the normal pathway and instead is due to retrograde conduction (conduction comes from the ventricles or from the AV node into and through the atria).[4].

Causes

Junctional bradycardia

Junctional tachycardia

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.

Related Chapters

References

  1. Merriam-Webster dictionary > Junctional rhythm Retrieved September 2010
  2. Kim D, Shinohara T, Joung B, Maruyama M, Choi EK, On YK; et al. (2010). "Calcium dynamics and the mechanisms of atrioventricular junctional rhythm". J Am Coll Cardiol. 56 (10): 805–12. doi:10.1016/j.jacc.2010.03.070. PMC 3050609. PMID 20797495.
  3. eMedicine:"Junctional Rhythms" http://www.emedicine.com/MED/topic1212.htm
  4. medical dictionary http://medical-dictionary.thefreedictionary.com/retrograde+conduction
  5. "Junctional Rhythm: Overview - eMedicine". Retrieved 2008-12-21.

fi:Junktionaalinen rytmi


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