Cardiac rhythms arising from the atrioventricular (AV) junction occur as an automatic tachycardia or as an escape mechanism during periods of significant bradycardia with rates slower than the intrinsic junctional pacemaker.
The AV node (AVN) has intrinsic automaticity that allows it to initiate and depolarize the myocardium during periods of significant sinus bradycardia or complete heart block. This escape mechanism, with a rate of 40-60 beats per minute, produces a narrow QRS complex because the ventricle is depolarized using the normal conduction pathway. An accelerated junctional rhythm (rate >60) is a narrow complex rhythm that often supersedes a clinically bradycardic sinus node rate (see images below). The QRS complexes are uniform in shape, and evidence of retrograde P wave activation may or may not be present.
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Junctional bradycardia due to profound sinus node dysfunction. No atrial activity is apparent.
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Note the retrograde P waves that precede each QRS complex.
Less commonly, the AV junction develops abnormal automaticity and exceeds the sinus node rate at a time when the sinus rate would be normal (see image below). These junctional tachycardias are most often observed in the setting of digitalis toxicity, recent cardiac surgery, acute myocardial infarction, or isoproterenol infusion.
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Accelerated junctional rhythm is present in this patient. Note the inverted P waves that precede each QRS complex, with a rate of 115 bpm.
See Can't-Miss ECG Findings, Life-Threatening Conditions: Slideshow, a Critical Images slideshow, to help recognize the conditions shown in various tracings.
The junctional rhythm initiates within the AV nodal tissue. Accelerated junctional rhythm is a result of enhanced automaticity of the AVN that supersedes the sinus node rate. During this rhythm, the AVN is firing faster than the sinus node, resulting in a regular narrow complex rhythm. These rhythms may demonstrate retrograde P waves on ECG findings, and the rates can vary from 40-60 beats per minute.
Changes in autonomic tone or the presence of sinus node disease that is causing an inappropriate slowing of the sinus node may exacerbate this rhythm. Young healthy individuals, especially those with increased vagal tone during sleep, are often noted to have periods of junctional rhythm that is completely benign, not requiring any intervention.
Rarely, the AVN develops enhanced automaticity and overtakes a "normal" sinus node. This occasionally is observed in digitalis toxicity, following cardiac surgery (typically valve replacement), during acute myocardial infarction, or during isoproterenol infusion. Alteration in calcium metabolism in the sarcoplasmic reticulum causes accelerated junctional rhythm.[1]
Causes of junctional rhythm include the following:
Sick sinus syndrome (including drug-induced)
Digoxin toxicity
Ischemia of the AVN, especially with acute inferior infarction involving the posterior descending artery, the origin of the AV nodal artery branch.
Acutely after cardiac surgery, especially in children within 4 days after surgery for congenital cardiac defects; a literature review by Cools and Missant indicated that in patients undergoing surgery for congenital heart disease, the risk of junctional ectopic tachycardia is increased by surgery near the AV node, cardiopulmonary bypass operative time of over 90 minutes, young age, the use of inotropic drugs, and hypomagnesemia[2]
Acute inflammatory processes (eg, acute rheumatic fever, lyme disease), which may involve the conduction system
Diphtheria
Other drugs (eg, beta-blockers, calcium blockers, most antiarrhythmic agents) that cause sinus bradycardia
Junctional rhythms are common in patients with sick sinus syndrome or in patients who have significant bradycardia that allows the AV nodal region to determine the heart rate.
Sex-related demographics
Junctional escape rhythms, which are common in younger and/or athletic individuals during periods of increased vagal tone (eg, sleep), occur equally in males and females.
Age-related demographics
This rhythm may occur in persons of any age.
Junctional rhythms during sleep are common in children and in athletic adults.
No evidence suggests increased mortality. Prognosis is good.
Morbidity/mortality
The heart rate during a junctional rhythm often determines whether the patient has symptoms.
Presence of AV dissociation can lead to symptoms in patients because of atrial conduction and subsequent contraction when the tricuspid valve is closed (ie, canon a waves).
Periods of junctional rhythm are not necessarily associated with an increase in mortality. If an obvious cause is present, such as complete heart block or sick sinus syndrome, then the morbidity or mortality is directly related to that and not to the junctional rhythm mechanism, which is serving as a "backup rhythm" during the periods of bradycardia. Accelerated junctional rhythms may be a sign of digitalis toxicity.
Complications
Complications of junctional rhythm are usually limited to symptoms such as dizziness, dyspnea, or presyncope.
Accidental injury may result from syncope if the arrhythmia is not tolerated well.
Exacerbation of cardiac comorbidities, such as congestive heart failure and rate-related cardiac ischemia, may occur.
Junctional rhythms may be accompanied by symptoms or may be entirely asymptomatic. Note the following:
Palpitations, fatigue, or poor exercise tolerance: These may occur during a period of junctional rhythm in patients who are abnormally bradycardic for their level of activity.
Dyspnea: Sudden onset of symptoms and sudden termination of symptoms may occur, especially in the setting of complete heart block.
Presyncope (near syncope): The underlying cause of the junctional rhythm is the most significant predictor of symptoms. For instance, AV dissociation with complete heart block, defined as an atrial rate that is faster than the junctional escape rate, is more likely to cause symptoms than AV dissociation with a sinus rate slower than the competing junctional pacemaker. Additionally, syncope or presyncope may occur from an acute decrease in heart rate.
A predominant junctional rhythm may be associated with structural heart disease, sick sinus syndrome, or both, during which the junctional escape rhythm supersedes the sinus rate and provides a safety mechanism.
During a predominant junctional rhythm, the pulse usually is regular and the heart rate may be within reference range. Frequently, the junctional rhythm is 40-60 beats per minute.
Prominent jugular venous pulsations (ie, cannon a waves) may be present due to the right atrium contracting with a closed tricuspid valve.
Evaluation of serum electrolyte levels is generally indicated for patients with comorbidities that may predispose them to accelerated junctional rhythms because of intrinsic bradycardia or AV block. Suggested evaluations include the following:
Check digoxin level in patients on digoxin and obtain a 12-lead ECG.
The standard approach includes an electrolyte evaluation, a 12-lead ECG, a detailed history, and a physical examination.
Check a lyme titer and treat empirically with antibiotics in patients with possible tick exposure in endemic areas.
Junctional rhythms are common during sleep in younger patients.
Obtain a 2-dimensional echocardiograph in patients with suspected structural heart disease.
Obtain a stress echocardiograph or nuclear imaging test in patients with symptoms consistent with coronary ischemia.
Electrocardiography
The 12-lead electrocardiogram (ECG) is essential to making the correct diagnosis of any junctional rhythm (see images below). Telemetry strips demonstrating the onset and termination pattern of the unknown narrow complex rhythm often provide clues regarding the diagnosis. The 12-lead ECG findings also help identify patients with underlying structural heart disease or conduction abnormalities.[3]
View Image
Junctional bradycardia due to profound sinus node dysfunction. No atrial activity is apparent.
View Image
Note the retrograde P waves that precede each QRS complex.
View Image
Accelerated junctional rhythm is present in this patient. Note the inverted P waves that precede each QRS complex, with a rate of 115 bpm.
Note the following:
Determine if the rhythm is regular or irregular, if it is narrow or wide, if P waves are present, if the P waves are from the right atrium (upright in I and II, negative in aVL), how the rhythm was initiated and how it terminated, and, finally, the clinical setting in which the rhythm occurred.
A junctional rhythm usually presents with rates from 40-60 beats per minute.
Frequently, retrograde P-wave conduction may be notable as a negative P wave in leads I and II and positive in aVL. Because the arrhythmia is originating from within the nodal tissue, near simultaneous activation of the atrium and ventricle occurs. Thus, the P-wave or atrial activation may be hidden within the QRS complex and may not be noticeable on surface ECG findings.
Explore the differential diagnosis of a regular narrow complex tachycardia when interpreting the ECG findings. An unusually slow presentation of a tachycardia also may mimic a junctional escape rhythm. These include AV reentry via an accessory pathway, atrial tachycardia, and AV nodal reentrant tachycardia.
The differential of a junctional rhythm at lower rates includes a normal response to increased vagal tone during sleep and sinus bradycardia, inappropriate sinus bradycardia, and underlying AV block.
ECG findings may help rule out structural or congenital heart disease in patients with evidence of multiple forms of supraventricular arrhythmias.
A cardiac event monitor is indispensable for patients who are difficult to diagnose, such as those with transient symptoms of palpitations or minimal documentation of an abnormal rhythm. Patients may carry the event monitor for an indefinite period (usually 30 d) and press a button to record a rhythm strip during symptoms. The onset and termination of the rhythm is documented and may help guide therapy and may help exclude more potentially lethal arrhythmias, such as ventricular tachycardia, as a cause of the symptoms.
An implantable loop recorder may help diagnose junctional rhythm in patients with very infrequent symptoms.
In patients with an accelerated junctional rhythm after cardiac surgery, documentation of AV conduction is imperative. The accelerated junctional rhythm may be a manifestation of inflammation and/or damage to the AV junction; once the accelerated rhythm resolves, AV block may be present. If atrial epicardial wires are present, pacing the atrium at a more rapid rate allows verification of AV conduction.
If the diagnosis is still not certain, an electrophysiologic study (EPS) or invasive electrophysiologic evaluation can be performed.[4]
An electrophysiologic study (EPS) should reveal a His bundle depolarization preceding every QRS complex. The His-ventricular interval should be normal unless conduction system disease is present. AV and VA conductions often fluctuate.
Most of the workup on an otherwise healthy patient can be completed in an outpatient setting. Documentation of the arrhythmia on a rhythm strip is essential to properly diagnose the rhythm and to help exclude other causes.
AV nodal junctional rhythms generally are well tolerated; however, bradycardia for prolonged periods often causes symptoms such as dizziness and presyncope or, rarely, frank syncope in younger patients. Patients with coronary artery disease, those with significant comorbidities, or elderly patients may not tolerate a secondary junctional rhythm well and, in the acute setting, may require intervention such as a pacemaker.
Currently, the choices of treatment strategy include determination of the underlying cause and whether it is a normal physiologic response (ie, that observed in a young athlete) or due to a primary cardiac abnormality such as heart block.
The decision to treat a junctional rhythm depends on the underlying cause and the stability of the patient.[5] Note the following:
No pharmacologic therapy is needed for asymptomatic, otherwise healthy individuals with junctional rhythms that result from increased vagal tone.
In patients with complete AV block, high-grade AV block, or symptomatic sick sinus syndrome (ie, sinus node dysfunction), a permanent pacemaker may be needed. The junctional rhythm serves as an escape mechanism to maintain the heart rate during periods of bradycardia or asystole and should not be suppressed.
Emergency department care can include evaluation of the 12-lead ECG findings, airway protection and oxygenation, and blood pressure support, depending on the cause of the rhythm.
If the junctional rhythm is due to digitalis toxicity, then atropine, digoxin immune Fab (Digibind), or both may be necessary. In refractory cases of symptomatic digitalis toxicity that results in junctional tachycardia and causes severe symptoms, then intravenous phenytoin can be used. This should be administered in a monitored setting because of possible hypotension or the need for a pacemaker after resolution of the ectopic junctional rhythm.
Consultations
Symptomatic cases may benefit from a consultation with a cardiologist and/or an electrophysiologist to better define the etiology and approach to prevention.
If junctional rhythm is due to symptomatic sick sinus syndrome, permanent pacemaker implantation is indicated.
If ectopic junctional tachycardia, which usually occurs in the pediatric population, is incessant and symptomatic, then radiofrequency ablation via a percutaneous approach is indicated.[6]
Clinical Context:
Immunoglobulin fragment with a specific and high affinity for both digoxin and digitoxin molecules. Removes digoxin or digitoxin molecules from tissue binding sites.
Each vial of Digibind contains 40 mg of purified digoxin-specific antibody fragments, which bind approximately 0.6 mg of digoxin or digitoxin. Dose of antibody depends on total body load (TBL) of digoxin; estimates of TBL can be made in 3 ways, as follows:
(1) Estimate quantity of digoxin ingested in acute ingestion and assume 80% bioavailability (amount ingested [mg] X 0.8 = TBL).
(2) Obtain a serum digoxin concentration and, using a pharmacokinetics formula, incorporate the Vd of digoxin and the patient's body weight in kg (TBL = digoxin serum level [ng/mL] X 6 L/kg X body weight in kg).
(3) Use an empiric dose based on average requirements for an acute or chronic overdose in an adult or child.
If the quantity of ingestion cannot be estimated reliably, administer empirically (safest to use the largest calculated estimate); alternatively, be prepared to increase dosing if resolution is incomplete.
What is a cardiac junctional rhythm?What is the pathophysiology of junctional rhythm?What are risk factors for junctional rhythm?Which patients are at highest risk for junctional rhythm?In what age group are junctional rhythms most common?What is the prognosis of junctional rhythm?What is the mortality and morbidity associated with junctional rhythm?Which clinical history is characteristic of junctional rhythm?Which physical findings are characteristic of junctional rhythm?What causes junctional rhythm?What are the differential diagnoses for Junctional Rhythm?What is the role of lab studies in the workup of junctional rhythm?What is the role of imaging studies in the workup of junctional rhythm?What is the role of cardiac event monitoring in the evaluation of junctional rhythm?What is the role of an electrophysiology study in the workup of junctional rhythm?What are the treatment options for junctional rhythm?What is the role of medical care in the treatment of junctional rhythm?What is the role of surgery in the treatment of junctional rhythm?Which specialist consultations are needed for the treatment of junctional rhythm?What are complications from treatment of junctional rhythm?Which medications in the drug class Antiarrhythmic agents, Class 1-B are used in the treatment of Junctional Rhythm?Which medications in the drug class Antidigitalis agents are used in the treatment of Junctional Rhythm?Which medications in the drug class Anticholinergics are used in the treatment of Junctional Rhythm?
Sean C Beinart, MD, MSc, FACC, FHRS, Electrophysiologist, Cardiac Associates, PC; Medical Director, Center for Cardiac and Vascular Research, Washington Adventist Hospital; Assistant Medical Director, Arrhythmia Service, Frederick Memorial Hospital
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Steven J Compton, MD, FACC, FACP, FHRS, Director of Cardiac Electrophysiology, Alaska Heart Institute, Providence and Alaska Regional Hospitals
Disclosure: Nothing to disclose.
Chief Editor
Mikhael F El-Chami, MD, Associate Professor, Department of Medicine, Division of Cardiology, Section of Electrophysiology, Emory University School of Medicine
Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Medtronic; Boston Scientific<br/>Received grant/research funds from Medtronic Inc for principle investigator.
Acknowledgements
The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authors Jonathan Langberg, MD; Spencer Rosero, MD; Wojciech Zareba, MD, PhD, FACC; and David Huang, MD to the development and writing of this article.
Deal BJ, Wolff GS, Gelband H. Current Concepts in Diagnosis and Management of Arrhythmias in Infants and Children. New York, NY: Futura Publishing; 1998. 73-5.
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