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 or congenital JET. Pathophysiology
In normal individuals, electrical activity in the heart is initiated in the sinoatrial (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. 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.
In this procedure, the small area in which the cells initiating JET are found can be destroyed by heating or freezing the tissue. This is accomplished using wires passed to the heart via the femoral vein through a small puncture in the groin. The main risk of this procedure is accidental damage to the AV node. This occurs more frequently when treating JET than other forms of supraventricular tachycardia, requiring treatment with a pacemaker in 5-10% of ablations for JET. The risk is lower if the tissue is frozen rather than heated.For those at risk of developing JET such as children undergoing heart surgery, treatment can also be given prophylactically. A meta-analysis of 9 studies found that sedation with dexmedetomidine reduced the risk of JET occurring post-operatively. Epidemiology
JET is most commonly seen in children following cardiac surgery. The arrhythmia affects 2-22% of children depending on the type of surgery performed, with higher rates seen following repair of Tetralogy of Fallot, and lower rates following the repair of ventricular septal defects and arterial switch operations. Etymology
Junctional ectopic tachycardia derives its name from the problem it causes. "Junctional" is used as the abnormal tissue driving the ventricular rate is located close junction between the atria and ventricles, known as the AV node. Ectopic (from the Greek ektopos, meaning "out of place") refers to the fact that the ventricles are being triggered by tissue that is not the normal pacemaker tissue within the heart.