Background
Junctional ectopic tachycardia (JET) is characterized by rapid heart rate for a person's age that is driven by a focus with abnormal automaticity within or immediately adjacent to the atrioventricular (AV) junction of the cardiac conduction system (ie, AV node–His bundle complex). It does not have the electrophysiologic features associated with reentrant tachycardia (eg, AV node reentry) because this form of tachycardia does not respond to a single extrastimulus, does not convert with programmed stimulation or cardioversion, and may or may not have ventriculoatrial (VA) dissociation; also, administration of adenosine results in VA dissociation without termination. The QRS is usually normal, and retrograde P waves may be seen in the terminal portion of the QRS.
JET primarily occurs in two forms: idiopathic chronic junctional ectopic tachycardia, which is observed in the setting of a structurally normal heart, and transient postoperative junctional ectopic tachycardia occurs following repair of congenital heart disease.
In addition, nonparoxysmal junctional tachycardia is a related but rare pattern of arrhythmia that can be observed in the setting of digoxin toxicity.
For patient education resources, see Heart Health Center, as well as Supraventricular Tachycardia.
Pathophysiology
The pathophysiology of JET is unclear. Postoperative JET is associated with manipulation within the crux of the heart. It is believed to be secondary to trauma, infiltrative hemorrhage, or inflammation of the conduction tissue. [1] The incidence of JET after cardiac surgery is approximately 14%. Specifically, tetralogy of Fallot repair and longer aortic cross clamp times increase the risk of developing postoperative JET. [2] Congenital JET is rare and difficult to control. It is most often incessant, and many patients require multiple antiarrhythmic medications, ablation, and even pacemaker insertion due to resultant complete AV node block.
As implied by the synonym junctional automatic tachycardia, the mechanism may be automaticity. Others have suggested that triggered activity is responsible for this disorder. [3]
The location of the responsible tissue is probably truly ectopic to the primary conduction pathway of the AV junction because JET has been successfully treated by the application of radiofrequency catheter lesions without the production of AV block. Intracardiac mapping shows a normal heart volume interval and VA dissociation, or VA association if VA conduction is present.
Junctional acceleration, albeit at a lesser rate than typical JET, is a recognized phenomenon during and following radiofrequency energy delivery for modification of slow pathway conduction in the therapy of AV node reentry.
Histamine, eosinophil cation protein, or other products of mast cell, eosinophil, or basophil degranulation that are liberated in response to cardiopulmonary bypass have been implicated in the genesis of transient postoperative JET. The relative levels of various cytokines may also play a role. Low magnesium levels have been noted in children who develop JET following cardiopulmonary bypass surgery.
Etiology
The speculative causes of postoperative JET are discussed in Pathophysiology. The one fairly uniform finding is a preceding cardiopulmonary bypass surgery.
Postoperative JET occurs more often after tetralogy of Fallot repair. [4] It has been associated with resection of muscle bundles, increased traction through the right atrium for relief of right ventricular outflow tract obstruction, and with higher bypass temperatures.
The cause of congenital JET is unknown. A family history of JET has been reported in 50-55% patients. It appears that patients with the angiotensin-converting enzyme insertion/deletion (ACE D/D) polymorphism have a greater than 2-fold increase in the incidence of postoperative JET. Therefore, it is hypothesized that the renin-angiotensin-aldosterone system plays an important role in the etiology of JET. [5]
The nonparoxysmal form of junctional tachycardia, which may be a triggered arrhythmia, is observed following digoxin overdose.
Epidemiology
United States data
Postoperative junctional ectopic tachycardia (JET) occurred in 5.6% of 594 patients who underwent cardiac surgery. [6] JET was seen more frequently with postoperative use of dopamine and in younger patients.
International data
In one series, postoperative JET was identified in 7.5% of young patients undergoing Fontan procedures. Another series described JET in 10.2% of 874 pediatric patients undergoing cardiopulmonary bypass. [7]
Postoperative JET that required intervention was identified in 1.5% of infants undergoing the arterial switch procedure. It was also seen in 21.9% of patients who had undergone cardiac surgery for tetralogy of Fallot. [1]
Age
JET is one of the rarest forms of supraventricular tachycardia in infants. Congenital JET is presumed to be present from birth but may not be identified until months or years later.
Postoperative JET most commonly occurs in younger patients (it was found to occur more frequently in patients younger than 6 months) but is also known to occur in teenagers and adults after cardiopulmonary bypass surgery.
Prognosis
Spontaneous resolution of congenital junctional ectopic tachycardia (JET) has been observed in as many as one third of patients who reach age 1 year. Patients who continue to experience JET may do so at slower rates.
Curative attempts with radiofrequency catheter ablation therapy are probably warranted in patients with uncontrolled JET or if their size and age is sufficient to minimize procedural risks. Nevertheless, permanent AV block is a significant potential risk in the ablation of congenital JET.
Postoperative JET usually subsides after 36 hours without recurrence.
Morbidity/mortality
Although not a frequent type of arrhythmia, JET is one of the most serious and difficult-to-treat supraventricular tachycardias. Rare case reports have suggested that JET may be associated with progression to complete AV block. This does not appear to be the case in postoperative JET and has not been the author's experience in the rare cases of idiopathic JET.
Postoperative JET is usually transient and begins upon rewarming the patient. Its morbidity and mortality relates to the fact that it occurs at an extremely vulnerable period following cardiac surgery, when nodal inflammation and ischemia may be present and ventricular function is often diminished. The additional insults of poor ventricular filling because of tachycardia and the loss of AV sequential contraction are considered to significantly contribute to morbidity and mortality. However, if the JET rate is not too fast or is somewhat faster than the sinus node rate, it can be well tolerated until JET spontaneously subsides.
In a large series of patients with postoperative JET, dopamine use and an age less than 6 months were associated with the development of this tachycardia. [6] However, only 39% of patients required intervention.
Congenital JET occurs in neonates and infants as an incessant tachycardia that usually results in tachycardia-induced cardiomyopathy. Mortality in these patients has been reported to be as high as 35% [8] and may occur secondary to congestive heart failure, sudden onset of ventricular fibrillation, and sudden evolution to paroxysmal complete AV block and as result of proarrhythmic effect of drug therapy and medical interventions.
In fetuses with JET (as well as those with ventricular tachycardia) third-degree AV block should be ruled out. [9]
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Lead II rhythm strip of a surface ECG from a patient with postoperative JET. Atrial activity (P) is marked with blue lines and ventricular depolarization (QRS) is marked in red. Note the narrow QRS complexes due to their origin at the AV junction. Also note the dissociation between atrial and ventricular depolarizations where some of the QRS complexes seem to "follow" the P waves. However, this is not possible because the PR intervals are exceedingly short to allow conduction. In addition, some of the P waves fall after the QRS.
