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)
