A junctional escape beat is a delayed heartbeat

Cardiac cycle

The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...

 originating not from the atrium

Atrium (anatomy)

In anatomy, the atrium , sometimes called auricle , refers to a chamber or space. For example, the term is used for a portion of the lateral ventricle in the brain and the blood collection chamber of the heart...

 but from an ectopic

Cardiac ectopy

Ectopic beat is a disturbance of the cardiac rhythm frequently related to the electrical conduction system of the heart, in which beats arise from fiber or group of fibers outside the region in the heart muscle ordinarily responsible for impulse formation, i.e., the Sinus node...

 focus somewhere in the AV junction. It occurs when the rate of depolarization of the sinoatrial node

Sinoatrial node

The sinoatrial node is the impulse-generating tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava...

 falls below the rate of the atrioventricular node

Atrioventricular node

The atrioventricular node is a part of the electrical control system of the heart that coordinates heart rate. It electrically connects atrial and ventricular chambers...

. This dysrhythmia also may occur when the electrical impulses from the SA node fail to reach the AV node because of SA or AV block. It is a protective mechanism for the heart, to compensate for the SA node no longer handling the pacemaking activity, and is one of a series of backup sites that can take over pacemaker function when the SA node fails to do so.

Etiology

A junctional escape complex is a normal response that may result from excessive vagal tone on the SA node, a pathological slowing of the SA discharge, or a complete AV block.

ECG Characteristics

• Rate: 40-60 bpm
• Rhythm: Irregular in single junctional escape complex; regular in junctional escape rhythm.
• P waves: Depends on the site of the ectopic
  Cardiac ectopy
  Ectopic beat is a disturbance of the cardiac rhythm frequently related to the electrical conduction system of the heart, in which beats arise from fiber or group of fibers outside the region in the heart muscle ordinarily responsible for impulse formation, i.e., the Sinus node...
  
   focus. They will be inverted, and may appear before or after the QRS complex, or they may be absent, hidden by the QRS.
• P-R interval: If the P wave occurs before the QRS complex, the interval will be less than 0.12 seconds.
• QRS Complex: Usually normal in duration and morphology, less than 0.12 seconds.

Significance

Junctional rhythms (if a bradycardia

Bradycardia

Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...

), can cause decreased cardiac output. Therefore, the person may exhibit signs and symptoms similar to other bradycardia

Bradycardia

Bradycardia , in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beat/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their heart...

 such as lightheadedness

Lightheadedness

Light-headedness is a common and often unpleasant sensation of dizziness and/or feeling that one may be about to faint, which may be transient, recurrent, or occasionally chronic. In some cases, the individual may feel as though his or her head is weightless. The individual may also feel as...

, dizziness

Dizziness

Dizziness refers to an impairment in spatial perception and stability. The term is somewhat imprecise. It can be used to mean vertigo, presyncope, disequilibrium, or a non-specific feeling such as giddiness or foolishness....

, hypotension

Hypotension

In physiology and medicine, hypotension is abnormally low blood pressure, especially in the arteries of the systemic circulation. It is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the...

, and syncope

Syncope (medicine)

Syncope , the medical term for fainting, is precisely defined as a transient loss of consciousness and postural tone characterized by rapid onset, short duration, and spontaneous recovery due to global cerebral hypoperfusion that most often results from hypotension.Many forms of syncope are...

. Usually this rhythm can be tolerated if the rate is above 50 bpm.

See also

• Ectopic beat
• Junctional rhythm
  Junctional rhythm
  Junctional rhythm describes an abnormal heart rhythm resulting from impulses coming from a locus of tissue in the area of the atrioventricular node, the "junction" between atria and ventricles....