Junctional Rhythm

Etiology

When the electrical activity of the SA node is blocked or is less than the automaticity of the AV node/His bundle, a junctional rhythm originates. Numerous conditions and medications can lead to a diseased SA node and lead to the AV node/His bundle taking over due to the higher automaticity of the ectopic pacemaker.[7][8][9]

Some of these conditions and medications are listed below.

• Chest trauma                                                            
• Sick sinus syndrome
• Radiation therapy
• Collagen vascular disease
• Myocarditis
• Clonidine
• Reserpine
• Adenosine
• Cimetidine
• Antiarrhythmics class I to IV
• Lithium
• Amitriptyline
• Neuromuscular disorder
• X-linked muscular dystrophy
• Familial disorder
• Vasovagal simulation (endotracheal suctioning)
• Carotid sinus hypersensitivity
• Beta-blockers
• Calcium channel blockers
• Digoxin
• Ivabradine
• Opioids
• Cannabinoids
• Isoproterenol infusion
• Hypothyroidism
• Sleep apnea
• Hypoxia
• Intracranial hypertension
• Hyperkalemia
• Anorexia nervosa
• Amyloidosis
• Pericarditis
• Lyme disease
• Rheumatic fever
• Ischemic heart disease
• Acute myocardial infarction
• Acute and chronic coronary artery disease
• Repair of congenital heart disease
• Inherited channelopathy

Other than the above-listed causes of severe SA node disease, which can result in junctional rhythm, a high-grade second-degree heart block and a third-degree heart block can also result in a junctional rhythm. Digoxin toxicity can also lead to an accelerated junctional rhythm.

Epidemiology

Junctional rhythm is typical among individuals who have a sinus node dysfunction (SND), and 1 in every 600 cardiac patients above the age of 65 within the United States has SND. Patients with sick sinus syndrome, young children, and athletes who have increased vagal tone may also intermittently exhibit junctional rhythm, especially during sleep. Junctional rhythm is reported equally among males and females.[10]

Pathophysiology

A heart has numerous pacemaker sites within its conduction system, which are independently able to keep the heart beating. And the rate of a heartbeat depends upon the pacemaker site, and as we go down its conduction system, the rate of spontaneous depolarization at pacemaker sites decreases. [1][2][3]

Pacemaker sites and their depolarization rates are listed below:

• Sinoatrial node: 60 to 100 beats per minute 
• Atria: less than 60 beats per minute 
• Atrioventricular node: 40 to 60 beats per minute 
• Ventricles: 20 to 40 beats per minute

Histopathology

Histopathology of a disease SA node that can contribute to the AV node/His bundle taking over as a pacemaker secondary to their intrinsic automaticity includes SA node fibrosis, atrophy, hypoplasia, or amyloidosis. A normal SA node histopathology does not rule out reduced SA node automaticity contributing to a junctional rhythm.[11][12]

History and Physical

Patients with junctional rhythm may present with a varied array of symptoms or may be asymptomatic. Symptoms mostly depend on the underlying cause of the junctional rhythm, for instance, a patient presenting with heart failure exacerbation may present with shortness of breath, wheezing, and lower extremity edema. Patients with rheumatic fever may present with a heart murmur secondary to the damage to the heart valves, fever, joint pain, and a rash with an electrocardiogram showing a junctional rhythm. Some patients might present with generalized complaints such as dizziness, fatigue, syncope/presyncope, and intermittent palpitations. Non-specific physical exam findings include pulsating veins and regular heart rate with the heart rate varying from 20 to over 100 beats per minute.[13][14][15]

Evaluation

A significant component of an assessment for a patient who presents with signs and symptoms of junctional rhythm is history and physical exam. These should include vital signs (respiratory rate, blood pressure, temperature, and heart rate), a review of the patient's medication list, and an electrocardiogram. See the image below. During their evaluation, it should be established if the patient is hemodynamically stable. The patient should be assessed for any underlying ischemic heart disease or heart failure. A healthcare provider should consider thyroid function testing, pulmonary function testing, including routine blood work, and echocardiography as part of their initial evaluation.[13][14][15]

Treatment / Management

Treatment of a junctional rhythm primarily depends on the underlying cause of the rhythm. In circumstances where the junctional rhythm is a result of underlying sinus node dysfunction that is leading to asystole or bradycardia, it should not be terminated, for it is maintaining the heart rate. Therefore, before establishing a management plan for patients presenting with a junctional rhythm, an underlying etiology must be determined first. Otherwise, healthy individuals who have junctional rhythm and are asymptomatic need no medical management as the rhythm is usually a result of their increased vagal tone suppressing the SA node intrinsic automaticity. In the setting of digoxin toxicity, a patient must be treated with atropine and digoxin-specific antibody. If a patient is refractory to these pharmacologic treatments and goes into junctional tachycardia, intravenous phenytoin can be administered in a monitored setting as these patients can develop hypotension. In the pediatric population, persistent symptomatic junctional tachycardia is an indication for percutaneous radiofrequency ablation. In patients with sick sinus syndrome, or complete or high-grade AV block, a permanent pacemaker is indicated.[16][17][18][19][20](B2)

Differential Diagnosis

• Digoxin toxicity
• Atrioventricular nodal reentrant tachycardia
• Atrioventricular reentrant tachycardia
• Sinus node dysfunction
• High-grade second-degree heart block
• Third-degree heart block

Prognosis

Prognosis is good when the rhythm is promptly identified by a healthcare provider. 

Complications

If not identified promptly symptomatic complications such as syncope, fatigue, or dizziness can occur.