Junctional ectopic tachycardia (JET) is an arrhythmia present usually in infants and children. It originates in the atrioventricular (AV) node or AV junction, including the bundle of His (BH). It is further classified into congenital junctional ectopic tachycardia (CJET) and postoperative junctional ectopic tachycardia (POJET).
CJET occurs without any previous history of heart surgery and can be even present at birth. CJET is associated with high morbidity and mortality as high as 35 percent if not diagnosed and appropriately treated as it is usually refractory to medical therapy.
POJET usually occurs in the first 72 hours of repair of congenital heart defects. It has been attributed to ischemia, stretching, and direct injury to the atrioventricular (AV) conduction tissue of the heart during the repair of congenital defects. It can be regular or irregular. It does not involve the reentry circuit, unlike AV nodal reentry and AV reentry supraventricular arrhythmias. It could have retrograde atrial conduction in 1:1 pattern or AV dissociation with variable conduction.
Congenital junctional ectopic tachycardia can occur without any previous heart surgery and can be even present at birth. It usually occurs in the first six months after birth. Postoperative junctional ectopic tachycardia usually occurs in patients who underwent repair of congenital heart defects. The risk factors that increase the risk of postoperative JET are postoperative use of dopamine, milrinone, higher postoperative core temperatures, electrolyte abnormalities, age less than six months, prolonged duration of surgery, and the type of surgery.
In infants and children, congenital junctional ectopic tachycardia is extremely rare. Data from big electrophysiology centers over 40 years have only shown 100 cases. Postoperative junctional ectopic tachycardia is more common and has been seen up to 5 percent of the cases after cardiac surgery.
Enhanced and abnormal automaticity has been described as the primary pathophysiologic mechanism underlying congenital junctional ectopic tachycardia. This is why this arrhythmia is refractory to intravenous adenosine and direct current cardioversion. It does not involve AV nodal reentry, which differentiates it from AV nodal reentry supraventricular tachycardias. Multiple gene deletions have been proposed as the underlying genetic abnormality, which includes angiotensin-converting enzyme insertion/deletion and troponin-I interacting kinase. Troponin-I interacting kinase mutation has been implicated in dilated cardiomyopathy seen in patients with congenital JET.
Congenital junctional ectopic tachycardia usually occurs in infants less than six months old, but diagnosis can be delayed after six months as well. Patients typically have heart rates of 200 to 250 beats per minute. Patients can develop fetal tachycardia prenatally and present as congestive heart failure or hydrops in the fetus.
Infants can present with dyspnea with dilated cardiomyopathy at presentation, ventricular fibrillation, and also complete heart block leading to sudden cardiac death. Mortality as much as 35 percent as been reported in the past, although more recent reports show mortality of 4 to 9 percent. Younger infants have more incessant tachycardia than older infants and thus higher mortality.
The clinical characteristics are gradual onset with the warm-up phase and cooling down phase with rate variability. Postoperative JET usually presents within 72 hours after surgery. On physical examination, the patient is noted to have tachycardia with signs of congestive heart failure. Cannon waves may be seen in jugular venous pulse if ventriculoatrial dissociation has occurred.
The patient should be evaluated for electrolyte abnormalities and acidosis. A chest x-ray should be done to evaluate for cardiomegaly and pulmonary edema. An electrocardiogram should be checked to assess for narrow complex tachycardia. It usually presents with intermittent ventriculoatrial dissociation with irregular ventricular rates. If there is 1 to 1 ventriculoatrial conduction, then the ventricular and atrial rate will be the same. It may be challenging to differentiate it from AV nodal reentry and AV reentry tachycardia.
Intravenous adenosine will cause ventriculoatrial dissociation in such cases and will show atrial nonparticipation in the arrhythmia. Very rarely, patients can have both JET and complete heart block. An echocardiogram shows cardiac dilation with systolic dysfunction related to tachycardia-induced cardiomyopathy.
Electrolytes should be corrected in case of electrolyte abnormalities. Amiodarone is the drug of choice and is given as a loading dose followed by a maintenance infusion. It can be used alone but is often used with other medications, including propranolol and flecainide. Intravenous adenosine does not terminate this arrhythmia given the absence of AV nodal reentry in JET.
Ivabradine has also been seen as an effective medication for congenital JET. Multiple medications can increase the risk of sudden cardiac death due to proarrhythmic effects. In postoperative JET, induction of hypothermia can also control these arrhythmias. Magnesium sulfate infusion preoperatively can also decrease the risk of these arrhythmias. Postoperative JET usually resolves within 72 hours. Dexmedetomidine, propafenone, procainamide, and sotalol have also been used in treating postoperative JET. Catheter ablation has been reserved for refractory cases.
Congenital junctional ectopic tachycardia is a more difficult arrhythmia to treat with higher morbidity and mortality as compared to postoperative junctional ectopic tachycardia. POJET usually responds better to treatment and is self-limited within 72 hours of its onset. Earlier reports showed CJET causing deaths in up to 35% of the cases as opposed to more recent reports of 4% to 9%.
Congenital junctional ectopic tachycardia can lead to cardiac dilation due to its incessant nature, and the cause of death is congestive heart failure, ventricular fibrillation, or complete heart block. Postoperative junctional ectopic tachycardia usually causes hypotension but has better response rates than CJET.
Pediatric electrophysiologists should be involved very early in these cases.
The patient's parents should be educated about symptoms and signs of this arrhythmia to recognize it promptly if it reoccurs after the patient is discharged. All treatment decisions should be discussed with them with all potential complications.
The nurses should report promptly any rhythm changes to the physicians. Any electrolyte abnormalities should also be reported to help physicians make the right decisions regarding treatment. The pharmacist has a critical role in making sure the doses of antiarrhythmic drugs are accurate, given the proarrhythmic nature of these drugs to prevent any unnecessary harm to the patients. With a better understanding of this arrhythmia and better treatment strategies, more recent reports show lower morbidity and mortality as compared to earlier reports.
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