• Junctional Rhythm
• ECG and Junctional Rhythm
• Junctional Tachycardia
• Junctional Tachycardia - Most Common Causes
• Junctional Tachycardia and AVNRT

Junctional Rhythm

• In junctional rhythm, impulses originate in the AV junction
• The AV junction consists of the AV node and the Bundle of His
• Each impulse then propagates from the AV junction
• To the atria (resulting in a negative - retrograde P wave)
• To the ventricles (resulting in a QRS complex)
• The junctional rhythm has a frequency of 40-60/min.

• Junctional rhythm is a secondary pacemaker, activated when:
• impulses stop arriving at the AV junction
• impulses arriving at the AV junction have a lower frequency than that generated by the AV junction
• The junctional rhythm is a protective mechanism, protecting the heart from
• Asystole (ventricular standstill)
• Severe sinus bradycardia
• If the junctional rhythm fails
• then a ventricular rhythm - a tertiary pacemaker - is activated

Junctional Rhythm

• Frequency: 50/min.
• Heart rhythm is regular: RR interval is constant
• Retrograde P wave: negative P wave before the QRS complexes
• PQ interval is shortened (< 0.12s)
• QRS complex is narrow (< 0.12s)
• Upper junctional rhythm
• Retrograde P wave is before the QRS complexes

Junctional Tachycardia - Most Common Causes

• Digoxin Intoxication (most common cause of accelerated junctional rhythm)
• Myocardial Infarction
• Occurs after cardiac surgical interventions

Junctional Tachycardia and AVNRT

• The AV junction can generate impulses through 2 mechanisms:
• Increased automaticity - results in junctional tachycardia
• Re-entry - results in AV Nodal Reentry Tachycardia (AVNRT)
• Differential diagnosis is done using supraventricular algorithms
• AVNRT generally has a higher frequency than junctional tachycardia

Junctional Tachycardia

• In the AV junction, there is increased automaticity
• Frequency is 100 - 130/min.
• Not triggered by atrial extrasystole
• Shows "warm up, cool down"
• Frequency slowly increases and slowly decreases

AVNRT

• In the AV junction, there is re-entry
• Frequency is 130 - 220/min.
• Occurs after atrial extrasystole
• Is paroxysmal
• Suddenly starts and suddenly ends

Junctional Tachycardia

• Frequency: 115/min.
• Frequency is > 100/min.
• Heart rhythm is regular: RR interval is constant
• Retrograde P waves: are before the QRS complexes
• This is an upper junctional rhythm (junctional tachycardia)
• QRS complex is narrow (< 0.12s)
• It could be:
• Junctional Tachycardia - increased automaticity of the AV junction
• AVNRT - re-entry in the AV junction
• Differential diagnosis of SVT

AV Nodal Re-entrant Tachycardia (AVNRT)

• Frequency: 160/min.
• Frequency is > 100/min.
• Heart rhythm is regular: RR interval is constant
• Retrograde P waves: are hidden within the QRS complexes
• QRS complex is narrow (< 0.12s)
• It could be:
• Junctional Tachycardia - increased automaticity of the AV junction
• AVNRT - re-entry in the AV junction
• Differential diagnosis of SVT
• It is most likely AVNRT
• Junctional tachycardia typically has a frequency < 140/min.
• Functional ST depressions - red arrows
• During tachycardia, myocardial ischemia occurs
• After normalizing the frequency, ST depressions resolve