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Under normal conditions, the heart's [[sinoatrial node]](SA node) determines the rate by which the organ beats – in other words, it is the heart's "pacemaker". The electrical activity of [[sinus rhythm]] originates in the sinoatrial node and depolarizes the atria. Current then passes from the atria through the atrioventricular node and into the [[bundle of His]], from which it travels along [[Purkinje fibers]] to reach and depolarize the ventricles. This sinus rhythm is important because it ensures that the heart's atria reliably contract before the ventricles.{{cn|date=February 2021}}
In junctional rhythm, however, the sinoatrial node does not control the heart's rhythm – this can happen in the case of a block in conduction somewhere along the pathway described above, or in sick sinus syndrome, or many other situations.<ref name="StatPearls" /> When this happens, the heart's [[atrioventricular node]] or [[bundle of His]] can take over as the pacemaker, starting the electrical signal that causes the heart to beat.<ref name="StatPearls" />
Junctional rhythm can be diagnosed by looking at an [[ECG]]: it usually presents without a P wave or with an inverted P wave. Retrograde, or inverted, P waves refers to the depolarization from the AV node back towards the SA node.<ref>Abnormalities in the ECG measurement http://library.med.utah.edu/kw/ecg/ecg_outline/Lesson4/index.html#PRinterval</ref>
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* Certain medications
* Other neuromuscular disorders
==Clinical presentation==
The presentation and symptoms a patient can present with are varied and often dependent on the underlying cause of the junctional rhythm. Patient's can be [[asymptomatic]] for example, or experience difficulty breathing and chest pain if they have underlying [[congestive heart failure]]. Other nonspecific findings include dizziness, fatigue, [[palpitations]], and passing out. This diagnosis is made via ECG. <ref name="StatPearls" /><ref name="eMedicine" />
==Classes of junctional rhythms==
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