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Junctional rhythm

See brief interpretation of 12 lead EKG above

Junctional rhythms originate in the atrioventricular (AV) junction, which consists of the atrioventricular node and the bundle of His.

Remember that all cells of the conduction system have the potential to generate electrical impulses. Normally the higher frequency of the sinoatrial node (SA, sinus node) will override the other cells of the conduction system and drive the heart contractions. Junctional rhythms may originate as escape rhythms when sinus node activity becomes too slow or are blocked.

The rate of a junctional escape rhythm is 40-60 beats per minute. The P waves are conducted in a retrograde fashion (unless block or AV dissociation is present) and may precede, succeed or be hidden in the QRS complexes. Because of this retrograde activation of the atria the P waves (if visible) will appear negative in the inferior leads (II, III, aVF). The QRS complexes are often narrow, but may be wide due to bundle branch block (as in the EKG in this article).

Junctional rhythms may also override the sinus node simply by firing at a faster rate. This is called accelerated junctional rhythm as the rate is faster than normal for the AV junction. The rate of accelerated junctional rhythm is 60-100 beats per minute. If the rate is more than 100 beats per minute the rhythm is called junctional tachycardia.

Accelerated junctional rhythm may be due to digitalis intoxication or heart disease and is seldom seen in normal individuals. Junctional escape rhythm is seen in normal individuals (due to increased parasympathetic activity) but also as a result of heart blocks.

— Mathias

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