Junctional Rhythm

Junctional Rhythm 

Junctional rhythm is an abnormal cardiac rhythm originating in the His bundle or atrioventricular (AV) node.

This diagnosis includes three distinct entities based on rate:

• 1.A junctional escape rhythm has a rate of 40 to 60 bpm.
• 2.Accelerated junctional rhythm has a rate of 60 to 100 bpm.
• 3.Junctional ectopic tachycardia (JET) has a rate of >100 bpm.

Synonyms

• Junctional escape rhythm
• Accelerated junctional rhythm
• Junctional ectopic tachycardia (JET)
• Nodal rhythm disorder
• Ectopic rhythm disorder
• Junctional premature depolarization

Incidence

Junctional rhythm occurs more commonly in children because of higher vagal tone (13% of 10- to 13-yr-old boys, 45% of 7- to 10-yr-old children, and 19% of infants have junctional rhythm during sleep).

Endurance athletes have a 20% incidence of junctional rhythm, for a similar reason.

Prevalence

Junctional tachycardia is a rare cause of supraventricular tachycardia. It is rare in the pediatric population and even less common in adults.

On the contrary, junctional rhythm is common although the prevalence is not well defined.

Risk Factors

Conduction system disease, heart block, digitalis intoxication, heart surgery, endocarditis.

Genetics

There is no known hereditary component to any of the aforementioned junctional rhythms.

Physical Findings & Clinical Presentation

Essential History

• •Previous history of syncope, presyncope, lightheadedness.
• •Drugs, especially digoxin. Amount taken, time of ingestion. The digestion time is especially important because the serum digoxin level ideally should be measured at least 6 hr after ingestion to ensure accuracy. Obtain a thorough medication history to determine if any recent additions or dosing changes were made. Presence of renal failure can result in higher or even toxic serum levels of digoxin. Hypokalemia renders cardiac tissue more susceptible to the effects of digoxin and should be promptly corrected in the event of digoxin toxicity. Other medications such as beta-blockers and nondihydropyridine calcium channel blockers may also result in a junctional escape rhythm primarily by causing AV block.

Symptoms

• •Lightheadedness
• •Syncope
• •Palpitations
• •Symptoms associated with digitalis intoxication: Gastrointestinal symptoms such as anorexia, nausea, vomiting, and abdominal pain. Neurologic manifestation such as lethargy, fatigue, delirium, confusion, weakness. Visual changes: Alteration in color vision, diplopia, photophobia, decreased visual acuity

Physical Examination

• •Vital signs
• •Look for evidence of hypoperfusion and end organ dysfunction
• •Cannon A-waves on examination of the jugular pulse

Etiology

Junctional tachycardia can occur as a primary arrhythmia (usually in children-JET), secondary to digitalis intoxication or catecholamine intoxication, or in the setting of injury to the His bundle (e.g., after valve surgery, abscess, sarcoidosis, myocarditis, ischemia).

Diagnosis

Differential Diagnosis

• •AVNRT (atrioventricular nodal reentrant tachycardia)
• •AVRT (atrioventricular reentrant tachycardia)
• •Accelerated idioventricular rhythm, in the case of junctional rhythm with aberrant conduction

Workup

• •Vital signs
• •12-lead ECG. The rhythm is almost perfectly regular and the QRS complex is generally narrow and similar to the complex seen during sinus rhythm. Retrograde P waves with a very short interval from QRS to P wave can be seen
• History of cardiac surgery, fevers, drug ingestion

Laboratory Tests

• •Serum digoxin concentration
• •Serum potassium concentration
• •Creatinine and blood urea nitrogen (BUN) to assess renal function
• •Troponin
• •Serum antibody testing for Lyme disease, if junctional escape rhythm is associated with AV block

Imaging Studies

Echocardiogram

Treatment

Junctional tachycardia may be a marker for a serious underlying condition such as digitalis toxicity, post cardiac surgery, endocarditis, hypokalemia, or myocardial ischemia. Underlying conditions should be sought and corrected accordingly.

Nonpharmacologic Therapy

• •Junctional escape rhythm in the setting of sinus arrest or complete heart block without reversible cause necessitates permanent pacemaker implantation.
• •Junctional ectopic tachycardia can be treated with antiarrhythmics or radiofrequency ablation.

Electrophysiology study

The origin of this tachycardia is within the His bundle or AV node, and it can be diagnosed definitively by intracardiac recordings.

Junctional rhythm most frequently takes the form of escape rhythms in the presence of sinus node dysfunction or AV nodal block, which can be diagnosed on electrophysiology (EP) study.

These escape rhythms usually have a QRS morphology identical to that seen during sinus rhythm. In such cases there is no P wave before the QRS complexes.

The P waves can occur simultaneously with the QRS complexes; more commonly, they are retrograde.

When the junctional rhythm is faster than 100 beats/min, it is called junctional tachycardia.

Acute General Treatment

The mainstay of managing nonparoxysmal junctional tachycardia is to correct the underlying abnormality.

Withholding digitalis when junctional tachycardia is the only clinical manifestation of toxicity is usually adequate.

If, however, ventricular arrhythmias or high-grade heart block are observed, then treatment with digitalis-binding agents may be indicated.

Disposition

Admit to cardiac telemetry if symptomatic. Consider specialty referral to cardiac electrophysiology.

Referral

Refer to cardiologist.

Pearls & Considerations

• •Junctional rhythm often is observed in patients with AV dissociation, which can lead to atrial contraction against closed atrioventricular valves, resulting in cannon A waves. This wave will cause pulsation in the neck and abdomen, headache, cough, jaw pain and possible hypotension.
• •The presence of a slow (30-40 bpm) and perfectly regular rhythm in a patient with atrial fibrillation often indicates junctional rhythm with complete heart block.

Prevention

N/A

Seek Additional Information

• Drago F., et al.: Neonatal and pediatric arrhythmias: clinical and electrocardiographic aspects. Card Electrophysiol Clin 2018; 10 (2): pp. 397-412.
• Page R.L., et al.: 2015 ACC/AHA/HRS guideline for the management of adult patients with supraventricular tachycardia: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Amer Col Card 2016; 67 (13): pp. e27-e115.