• Heart Rhythm
• Junctional Rhythm
• Junctional Rhythm - Most Common Causes
• Sinus Rhythm and Junctional Rhythm
• P Wave and Junctional Rhythm
• Upper Junctional Rhythm
• Middle Junctional Rhythm
• Lower Junctional Rhythm
• ECG and Junctional Rhythm
• Frequency and Junctional Rhythm

Heart Rhythm

Basic Heart Rhythms

• Heart rhythm is determined by the site (sites) that generates impulses with the highest frequency (overdrive suppression)
• There are 3 basic heart rhythms
• Sinus rhythm (Impulses generated by the SA node)
• Junctional rhythm (Impulses generated by the AV junction)
• Ventricular rhythm (Impulses generated by the Purkinje fibers in the ventricles)
• Sinus rhythm is the physiological heart rhythm
• Because the sinoatrial (SA) node generates impulses with the highest frequency (overdrive suppression)
• The SA node is referred to as the primary pacemaker (the pace-setter)
• Junctional rhythm is a secondary pacemaker
• The AV junction generates impulses with the second highest frequency after the SA node
• Junctional rhythm occurs if
  • impulses from the atria cease to arrive at the AV junction
  • the AV junction starts generating impulses with a higher frequency than the atria

Junctional Rhythm - Most Common Causes

• Sinus Bradycardia
• Sinus Pause (Sinus Arrest)
• SA Block III Degree
• AV Block III Degree
• Hyperkalemia
• Beta Blockers
• Calcium Channel Blockers
• Digoxin

Junctional Rhythm

• Impulses are generated by the AV junction with a frequency of: 40-60/min.
• From the AV junction, the impulse spreads:
• to both the atria and the ventricles
• Ventricular vector moves toward lead II
• A QRS complex is formed
• Atrial vector moves toward the SA node
• Direction is away from lead II
• A negative - retrograde P wave is formed
• The ventricles are activated first (QRS) and then the atria (negative P wave)

Upper Junctional Rhythm

• Impulses originate in the upper part of the AV junction
• Each impulse simultaneously spreads to both the atria and the ventricles
• Atria are activated before the ventricles
• Because the impulse reaches the atria before it reaches the ventricles
• Shortened PQ interval (< 0.12s)
• Retrograde P wave is just before the QRS complex

Lower Junctional Rhythm

• Impulses originate in the lower part of the AV junction
• Each impulse simultaneously spreads to both the atria and the ventricles
• Ventricles are activated before the atria
• Because the impulse reaches the ventricles before it reaches the atria
• Retrograde P wave is just after the QRS complex

Junctional Rhythm

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

Junctional Bradycardia

• Frequency: 37/min.
• Junctional bradycardia has a frequency of < 40/min.
• Sinus bradycardia has a frequency of < 50/min.
• P waves are hidden within the QRS complex
• Impulses are generated by the middle part of the AV junction

Accelerated Junctional Rhythm

• Frequency: 75/min.
• Retrograde P waves occur after the QRS complexes
• Impulses are generated by the lower part of the AV junction

Junctional Rhythm

• Frequency: 48/min.
• P waves are hidden within the QRS complex
• Impulses are generated by the middle part of the AV junction
• Narrow QRS complexes (< 0.12s)
• The patient had SA node block III degree
• The SA node generates impulses, but all are blocked

Junctional Rhythm

• Frequency: 45/min.
• P waves are hidden within the QRS complex
• Impulses are generated by the middle part of the AV junction
• Narrow QRS complexes (< 0.12s)

Junctional Rhythm

• Frequency: 60/min.
• P waves after the QRS complexes (red arrows)
• Impulses are generated by the lower part of the AV junction
• Narrow QRS complexes (< 0.12s)

Junctional Rhythm and Isorhythmic AV Dissociation

• Sinus Rhythm
• Frequency: 44/min.
• Positive P waves AFTER QRS (II lead)
• Junctional Rhythm
• Never has positive P waves in the inferior leads (II, III, aVF)
• At a frequency of 44/min. from the SA node, a junctional rhythm was activated
• Also with a frequency of 44/min.
• There are 2 pacemakers in the heart:
• SA node - sinus rhythm
• AV junction - junctional rhythm
• Junctional Rhythm
• Frequency 44/min.
• Retrograde P wave of the junctional rhythm does not occur
• because the P wave originates from the SA node
• Just before the impulse from the SA node reaches the AV junction, the AV junction generates its own impulse.
• Then, just above the AV junction, the 2 impulses meet and cancel each other out during the (refractory period)
• Isorhythmic AV Dissociation
• It is the independence of the atria (P waves) from the ventricles (QRS) with the same frequency