Introduction

• A rhythm of junctional origin arises from the tissue of the atrioventricular (AV) node or bundle of His which form the junction of the atria and the ventricles

• Under normal circumstances, sinoatrial (SA) node acts as the primary pacemaker and generates sinus rhythm

• In certain situations, junctional rhythm may arise and replace the sinus rhythm as the tissue of the AV node (and bundle of His) has the ability to produce a sustained rhythm

• The most common situation is when the SA does not produce a rhythm to the rhythm it produces is too slow - sinus bradycardia; in this case the automaticity of the AV node (and bundle of His) is higher than the automaticity of the SA node and it therefore acts as a pacemaker

Pathophysiology

• Two distinct groups of people may have this condition
  - patients with sinus node dysfunction
  - children and athletes with high vagal tone (especially during sleep)

• Additional conditions that may cause junctional rhythm are:
  - Chest trauma, radiation therapy
  - Myocarditis, pericarditis
  - Vasovagal simulation, carotid sinus hypersensitivity
  - Hypothyroidism, sleep apnea, hypoxia, intracranial hypertension
  - Ischemic heart disease, acute myocardial infarction, acute and chronic coronary artery disease
  - Lyme disease, Rheumatic heart disease
  - Drugs, including antiarrhythmic drugs (e.g. adenosine, beta blockers, calcium channel blockers, digoxin    toxicity)
  - High grade second degree AV block, third-degree AV block

Clinical presentation 

• May vary and patients may have no symptoms
• Symptomatic patients (typically with underlying heart disease) may present with dizziness, fatigue, syncope/presyncope, intermittent palpitations or shortness of breath
• Evaluation of the patient should include history (especially medication list), ECG and should be assessed for underlying heart disease.

Classification (by rate)

• Junctional bradycardia: rate below 40 beats per minute
• Junctional escape rhythm: rate 40 to 60 beats per minute
• Accelerated junctional rhythm: rate of 60 to 100 beats per minute
• Junctional tachycardia: rate above 100 beats per minute

Junctional tachycardia

• junctional tachycardia is caused by abnormal automaticity in the AV node (or bundle of His) and is relatively common in children but rare in adults
• AV dissociation may be present

Management

• Asymptomatic healthy individuals generally do not require treatment
• Patients with sinus node dysfunction or high grade second degree AV block/complete heart block should be considered for pacemaker implantation
• If the junctional rhythm is a result of pharmacotherapy, it should be revised

ECG characteristics

• regular rhythm with a rate corresponding to the type of junctional rhythm
• no visible P waves or retrograde P waves
• narrow QRS complexes of normal morphology

ECG 1 Accelerated junctional rhythm with a rate of 69/min, no visible P waves, narrow QRS complexes (114ms)

ECG 2 Junctional escape rhythm with a rate of 46/min, no visible P waves, narrow QRS complexes (110ms)

References

1. https://www.ncbi.nlm.nih.gov/books/NBK507715/
2. https://litfl.com/junctional-escape-rhythm-ecg-library/
3. https://ecgwaves.com/topic/junctional-rhythm-junctional-tachycardia/

‍