Junctional rhythm: Difference between revisions
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Revision as of 18:18, 19 October 2012
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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,[1] 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
- The junctional rate may be rapid in which case the rhythm is referred to as a junctional tachycardia
Pathophysiology
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.[2]. 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).[3].
Causes
Junctional bradycardia
- 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
- Sinus bradycardia
- STEMI particularly inferior MI involving the posterior descending artery causing ischemia of the AV node due to poor perfusion in the AV nodal artery
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 Example
In the EKG shown below, AV dissociation is present 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.
The EKG shown below is 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
- ↑ Merriam-Webster dictionary > Junctional rhythm Retrieved September 2010
- ↑ eMedicine:"Junctional Rhythms" http://www.emedicine.com/MED/topic1212.htm
- ↑ medical dictionary http://medical-dictionary.thefreedictionary.com/retrograde+conduction
- ↑ "Junctional Rhythm: Overview - eMedicine". Retrieved 2008-12-21.