Characteristics of Junctional Rhythms

Junctional rhythms arise from the pacemaker cells around the AV junction.   The inherent rate of these junctional pacemaker cells is 40-60/min.   When an impulse arises from the AV junction it spreads both upward toward the atrium and downward toward the ventricles.   When the impulse travels upward toward the atrium, it is termed retrograde conduction.   When the impulse spreads downward toward the ventricles it is termed antegrade conduction.  

If the impulse depolarizes the atrium first, then in lead II a negative or retrograde P wave will be seen before the QRS complex.   If the atrium and the ventricles are depolarized simultaneously then the P wave will be hidden within the QRS complex and will not be seen.   If the atrium are depolarized after the ventricles then a a negative P wave will be seen after the QRS complex.

The three junctional rhythms that arise from the AV junction are junctional rhythm with a rate between 40-60/min,  accelerated junctional rhythm with a rate between 61-100/min, and junctional tachycardia with a rate between 100-150/min.

Junctional rhythms

The rhythm is regular with a heart rate between 40-60/min.   The P waves are inverted before or after the QRS complex or may be absent.   The PR interval is usually less than .10 sec and the QRS complex is normally less than .10 sec.  

Accelerated junctional rhythms

The rhythm is regular with a heart rate between 61-100/min.   The P waves are inverted before or after the QRS complex or may be absent.   The PR interval is usually less than .10 sec and the QRS complex is normally less than .10 sec.  

Junctional tachycardia

The rhythm is regular with a heart rate between 100-150/min.   The P waves are inverted before or after the QRS complex or may be absent.   The PR interval is usually less than .10 sec and the QRS complex is normally less than .10 sec. 

Characteristics of Junctional Rhythms

Type	Rhythm	Rate	P waves	PR interval	QRS complex
Junctional rhythm	regular	40-60/min	Inverted before or after the QRS complex or absent	usually < .10 sec	Normal, less than .10 sec
Accelerated Junctional rhythm	regular	60-100/min	Inverted before or after the QRS complex or absent	usually < .10 sec	Normal, less than .10 sec
Junctional tachycardia	regular	> 100/min	Inverted before or after the QRS complex or absent	usually < .10 sec	Normal, less than .10 sec

Examples of Junctional Rhythms

Junctional Rhythm

The rhythm is regular with a rate of 50/min.   The P waves are negative and precede the QRS complexes.   No ectopic beats are present.   QRS:  .08 sec,  QT:  .40 sec.   

Accelerated Junctional Rhythm

The rhythm is regular with a rate of 93/min.   The P waves are negative and precede the QRS complexes.   No ectopic beats are present.   QRS:  .08 sec,  QT:  .38 sec.   

Junctional Tachycardia

The rhythm is regular with a heart rate of 125/min.   The P waves are negative and follow the QRS complexes.   No ectopic beats are present.   QRS:  .08 sec,  QT:  .36 sec.   

Junctional Rhythm Practice

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Answers


1.   Accelerated junctional rhythm
2.   Junctional rhythm
3.   Junctional tachycardia
4.   Junctional rhythm
5.   Accelerated junctional rhythm
6.   Junctional rhythm
7.   Junctional tachycardia
8.   Accelerated junctional rhythm
9.   Junctional rhythm
10. Junctional tachycardia

Summary of junctional rhythms

Junctional rhythms arise in the pacemaker cells of the AV junction.   A retrograde P wave maybe seen before the QRS complex, after the QRS complex, or be absent.   If the junctional rhythm is between 40-60/min then it is termed a junctional rhythm; if it is between 61-100/min then it is termed an accelerated junctional rhythm; and if the rate is between 100-150/min then it is termed junctional tachycardia.