Junctional bradycardia: Difference between revisions
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==Pathophysiology== | ==Pathophysiology== | ||
Normally, the [[atrioventricular node]] ([[AVN]]) can generate an escape rhythm of 40-60 beats per minute in case the [[sinoatrial node]] ([[SA node]]) or atrial pacemakers fail ([[sinus arrest]]) or slow ([[sinus bradycardia]]) or if there is [[complete heart block]]. This [[junctional escape rhythm]] generates a normal, narrow [[QRS complex]] rhythm at a rate below 60 beats per minute ( | Normally, the [[atrioventricular node]] ([[AVN]]) can generate an escape rhythm of 40-60 beats per minute in case the [[sinoatrial node]] ([[SA node]]) or atrial pacemakers fail ([[sinus arrest]]) or slow ([[sinus bradycardia]]) or if there is [[complete heart block]]. This [[junctional escape rhythm]] generates a normal, narrow [[QRS complex]] rhythm at a rate below 60 beats per minute (junctional bradycardia) as the electrical impulses once they are generated are conducted with normal velocity down the usual pathways. [[Retrograde P waves]] (i.e. upside down) [[P waves]] due to retrograde or backward conduction may or may not be present. | ||
==Causes== | ==Causes== | ||
Revision as of 14:22, 24 October 2012
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Synonyms and keywords: Junctional escape; junctional escape rhythm
Overview
Junctional bradycardia is a slow (40 to 60 beats per minute) narrow complex escape rhythm that originates in the atrioventricular node to compensate for slow or impaired conduction of pacemaker activity in the atrium.
Pathophysiology
Normally, the atrioventricular node (AVN) can generate an escape rhythm of 40-60 beats per minute in case the sinoatrial node (SA node) or atrial pacemakers fail (sinus arrest) or slow (sinus bradycardia) or if there is complete heart block. This junctional escape rhythm generates a normal, narrow QRS complex rhythm at a rate below 60 beats per minute (junctional bradycardia) as the electrical impulses once they are generated are conducted with normal velocity down the usual pathways. Retrograde P waves (i.e. upside down) P waves due to retrograde or backward conduction may or may not be present.
Causes
- 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
Epidemiology and Demographics
Age
Benign junctional rhythms are common during sleep in both children and athletic young adults.
Gender
Males and females are affected equally.
Natural History, Complications and Prognosis
The natural history and prognosis of the disease depends upon the underlying cause that triggered the junctional escape rhythm. A junctional escape rhythm during sleep is benign in children and young adults.
Diagnosis
Symptoms
Symptoms are more likely if the atrial rate is faster than the junctional rate (if AV dissociation or complete heart block is present) as compared with the scenario whereby the junctional rate is faster than the atrial rate. The following symptoms may be present:
Physical Examination
Vitals
Pulse
The pulse is regular at a rate of 40 to 60 beats per minute.
Neck
- Cannon a waves may be present if there is delayed atrial contraction against a closed tricuspid valve
Laboratory Findings
Based upon the patient's history and demographics, consideration should be given to checking the following:
- Digoxin levels
- Lyme titers in patients where the disease is endemic
Electrocardiography
A 12 lead EKG should be obtained to evaluate the rhythm. In so far as it may alter treatment, any co-existing rhythm disturbance that may have precipitated junctional bradycardia should be ascertained such as:
- AV dissociation
- Complete heart block
- Digitalis toxicity
- Sinus arrest
- Sinus bradycardia
- ST elevation MI
- The rate is 40-60 beats per minute.
- The rate is generally regular.
- The QRS complex is narrow.
- Retrograde p waves may be present due to retrograde conduction from the AV node. The p waves will be inverted in leads II and III.
- The p wave may be buried within the QRS complex and may not be discernable.
- A slow AV nodal reentry tachycardia (AVNRT) should be excluded.
EKG Examples
The EKG below shows a nodal escape rhythm. Note the lack of P or P' waves. Often the P' wave is hidden in the QRS as the nodal escape conducts down to the ventricle and up to the atrium in a fashion such that the QRS and P' wave occur simultaneously.
Copyleft images obtained courtesy of ECGpedia, http://en.ecgpedia.org.
Example of junctional escape rhythm / junctional bradycardia on telemetry:
{{#ev:youtube|S2xnOJfZOPI}}
Holter / Cardiac Event Monitoring
A cardiac event monitor may be helpful in patients with transient symptoms or palpitations to exclude other rhythms such as ventricular tachycardia.
Electrophysiologic Studies
- There is normal conduction in the His bundle, and the His-ventricular interval is normal.
- Preceding each QRS, there should be a His bundle depolarization
- AV conduction is variable
- VA conduction is variable
Treatment
Acute Management
- Avoid drugs that suppress the AV node as the junctional bradycardia may be the patient's only escape rhythm
- Treat symptomatic digitalis toxicity with atropine and digoxin immune Fab (Digibind)
Asymptomatic Patients
- Among healthy patients with heightened vagal tone, no treatment is necessary
Symptomatic Patients
- Permanent pacemaker placement in indicated in symptomatic patients with:
- Complete heart block
- High grade AV block
- Sick sinus syndrome