Junctional ectopic tachycardia
Encyclopedia
Junctional ectopic tachycardia (JET) is a rare syndrome of the heart that manifests in patients recovering from heart surgery. It is characterized by cardiac arrhythmia
, or irregular beating of the heart, caused by abnormal conduction from or through the atrioventricular node
(AV node). In newborns and infants up to 6 weeks old, the disease may also be referred to as His bundle tachycardia.
. Ectopic (from the Greek ektopos, meaning "out of place") means irregular in this case. Tachycardia (from the Greek takhys, meaning "swift", and kardia, meaning heart) means a swift heart rate.
By this definition, junctional ectopic tachycardia is an abnormally swift heart rhythm due to cells within the heart near the AV node.
(SA) node (located in the right atrium
), propagates to the atrioventricular
(AV) node, and then through the bundle of His
to the ventricles of the heart. (See electrical conduction system of the heart
).
The AV node acts as a gatekeeper, limiting the electrical activity that reaches the ventricles of the heart. This function of the AV node is important, because if the signals generated in the atria of the heart were to increase in rate (as they do during atrial fibrillation
or atrial flutter
), the AV node will limit the electrical activity that conducts to the ventricles. For instance, if the atria are electrically activated at 300 beats per minute, half those electrical impulses are blocked by the AV node, so that the ventricles are activated at 150 beats per minute (giving a pulse
of 150 beats per minute). Another important property of the AV node is that it slows down individual electrical impulses. This is manifest on the ECG
as the PR interval, which is about less than 200 milliseconds, the time from activation of the atria (manifest as the P wave
) and activation of the ventricles (manifest as the QRS complex
).
Individuals with JET have a "short-circuit" in their heart, where the electricity bypasses the AV node, causing the heart to beat faster than normal. The cause of the arrhythmia, the ectopic focus, is usually near the AV node in the triangle of Koch (a rough triangle with points at the coronary sinus, the tendon of Todaro, and the tricuspid valve).
Patients of heart surgery may experience an accelerated narrow complex tachycardia, usually within the first 24–48 hours (but occasionally longer) after surgery. There may be atrio-ventricular disassociation with more ventricular signals then atrial signals. The cause of JET is felt to be due to manipulation of the tissue surrounding the AV node during surgery, however debate exists regarding the exact cause as it is seen after procedures even without significant manipulation of this area.
JET-like symptoms can also manifest congenitally and in the first six months of life. This syndrome, which may also referred to as His bundle tachycardia, is resistant to therapy and can be difficult to treat.
A 1994 study at the Adolph Basser Institute of Cardiology found that amiodarone
, an antiarrhythmic agent
, could be used safely and relatively effectively.
JET occurring after the first six months of life is somewhat more variable, but may still be difficult to control. Treatment of non post-operative JET is typically with antiarrhythmic medications or a cardiac catheterization with ablation (removal of affected tissue). A cardiac catheterization may be performed to isolate and ablate (burn or freeze) the source of the arrhythmia. This can be curative in the majority of cases. The use of radiofrequency energy is infrequently associated with damage to the normal conduction due to the close proximity to the AV node, the normal conduction tissue. The use of cryotherapy (cold energy) appears to be somewhat safer, and can also be effective for the treatment of JET.
Cardiac dysrhythmia
Cardiac dysrhythmia is any of a large and heterogeneous group of conditions in which there is abnormal electrical activity in the heart. The heart beat may be too fast or too slow, and may be regular or irregular.Some arrhythmias are life-threatening medical emergencies that can result in cardiac...
, or irregular beating of the heart, caused by abnormal conduction from or through 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...
(AV node). In newborns and infants up to 6 weeks old, the disease may also be referred to as His bundle tachycardia.
Etymology
Junctional ectopic tachycardia derives its name from the problem it causes. "Junctional" refers to the AV node, located at the junction between the atria and ventriclesVentricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...
. Ectopic (from the Greek ektopos, meaning "out of place") means irregular in this case. Tachycardia (from the Greek takhys, meaning "swift", and kardia, meaning heart) means a swift heart rate.
By this definition, junctional ectopic tachycardia is an abnormally swift heart rhythm due to cells within the heart near the AV node.
Pathophysiology
In normal individuals, electrical activity in the heart is initiated in the sinoatrialSinoatrial 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...
(SA) node (located in the right atrium
Right atrium
The right atrium is one of four chambers in the hearts of mammals and archosaurs...
), propagates to the atrioventricular
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...
(AV) node, and then through the bundle of His
Bundle of His
The bundle of His, known as the AV bundle or atrioventricular bundle, is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the AV node to the point of the apex of the fascicular branches...
to the ventricles of the heart. (See electrical conduction system of the heart
Electrical conduction system of the heart
The normal intrinsic electrical conduction of the heart allows electrical propagation to be transmitted from the Sinoatrial Node through both atria and forward to the Atrioventricular Node. Normal/baseline physiology allows further propagation from the AV node to the ventricle or Purkinje Fibers...
).
The AV node acts as a gatekeeper, limiting the electrical activity that reaches the ventricles of the heart. This function of the AV node is important, because if the signals generated in the atria of the heart were to increase in rate (as they do during atrial fibrillation
Atrial fibrillation
Atrial fibrillation is the most common cardiac arrhythmia . It is a common cause of irregular heart beat, identified clinically by taking a pulse. Chaotic electrical activity in the two upper chambers of the heart result in the muscle fibrillating , instead of achieving coordinated contraction...
or atrial flutter
Atrial flutter
Atrial flutter is an abnormal heart rhythm that occurs in the atria of the heart. When it first occurs, it is usually associated with a fast heart rate or tachycardia , and falls into the category of supra-ventricular tachycardias. While this rhythm occurs most often in individuals with...
), the AV node will limit the electrical activity that conducts to the ventricles. For instance, if the atria are electrically activated at 300 beats per minute, half those electrical impulses are blocked by the AV node, so that the ventricles are activated at 150 beats per minute (giving a pulse
Pulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
of 150 beats per minute). Another important property of the AV node is that it slows down individual electrical impulses. This is manifest on the ECG
Electrocardiogram
Electrocardiography is a transthoracic interpretation of the electrical activity of the heart over a period of time, as detected by electrodes attached to the outer surface of the skin and recorded by a device external to the body...
as the PR interval, which is about less than 200 milliseconds, the time from activation of the atria (manifest as the P wave
P wave (electrocardiography)
In electrocardiography, during normal atrial depolarization, the main electrical vector is directed from the SA node towards the AV node, and spreads from the right atrium to the left atrium...
) and activation of the ventricles (manifest as the QRS complex
QRS complex
The QRS complex is a name for the combination of three of the graphical deflections seen on a typical electrocardiogram . It is usually the central and most visually obvious part of the tracing. It corresponds to the depolarization of the right and left ventricles of the human heart...
).
Individuals with JET have a "short-circuit" in their heart, where the electricity bypasses the AV node, causing the heart to beat faster than normal. The cause of the arrhythmia, the ectopic focus, is usually near the AV node in the triangle of Koch (a rough triangle with points at the coronary sinus, the tendon of Todaro, and the tricuspid valve).
Patients of heart surgery may experience an accelerated narrow complex tachycardia, usually within the first 24–48 hours (but occasionally longer) after surgery. There may be atrio-ventricular disassociation with more ventricular signals then atrial signals. The cause of JET is felt to be due to manipulation of the tissue surrounding the AV node during surgery, however debate exists regarding the exact cause as it is seen after procedures even without significant manipulation of this area.
JET-like symptoms can also manifest congenitally and in the first six months of life. This syndrome, which may also referred to as His bundle tachycardia, is resistant to therapy and can be difficult to treat.
Treatment
Treatment is aimed at slowing the rate by correcting acidosis, correcting electrolytes (especially magnesium and calcium), cooling the patient, and antiarrhythmic medications. Occasionally pacing of the atrium at a rate higher than the JET may allow improved cardiac function by allowing atrial and ventricular synchrony.A 1994 study at the Adolph Basser Institute of Cardiology found that amiodarone
Amiodarone
Amiodarone is an antiarrhythmic agent used for various types of tachyarrhythmias , both ventricular and supraventricular arrhythmias. Discovered in 1961, it was not approved for use in the United States until 1985...
, an antiarrhythmic agent
Antiarrhythmic agent
Antiarrhythmic agents are a group of pharmaceuticals that are used to suppress abnormal rhythms of the heart , such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation....
, could be used safely and relatively effectively.
JET occurring after the first six months of life is somewhat more variable, but may still be difficult to control. Treatment of non post-operative JET is typically with antiarrhythmic medications or a cardiac catheterization with ablation (removal of affected tissue). A cardiac catheterization may be performed to isolate and ablate (burn or freeze) the source of the arrhythmia. This can be curative in the majority of cases. The use of radiofrequency energy is infrequently associated with damage to the normal conduction due to the close proximity to the AV node, the normal conduction tissue. The use of cryotherapy (cold energy) appears to be somewhat safer, and can also be effective for the treatment of JET.