Junctional Ectopic Tachycardia

Etiology

The etiology of JET varies depending on whether it is congenital or postoperative in origin. However, both forms result from abnormal automaticity from the AV node, BH, or adjacent conduction tissues.

CJET

CJET can occur without any history of prior cardiac surgery and is often evident at birth or within the first 6 months of life. Although rare—representing less than 1% of pediatric arrhythmias—CJET carries significant morbidity and mortality, with rates as high as 35% if not appropriately diagnosed and treated. The underlying mechanisms include:

• Intrinsic abnormalities of the AV conduction system
  • Developmental defects during cardiac embryogenesis may result in areas of enhanced automaticity within the AV node or His bundle.
• Genetic predisposition
  • Familial clustering has been reported, although specific genetic mutations responsible for this phenomenon remain largely unidentified.
• Ion channel dysfunction
  • The altered function of ion channels regulating action potentials in the AV junction may contribute to the formation of abnormal impulses.
• Histopathologic changes
  • Rare autopsy findings have demonstrated hypertrophy, fibrosis, and disorganization of the AV node tissue, creating a substrate for ectopic pacemaker activity.

CJET is frequently refractory to standard antiarrhythmic therapy and may lead to heart failure or death if not aggressively managed.

POJET

POJET typically occurs in the early period after surgical repair of congenital heart defects, usually within the first 72 hours after surgery. This arrhythmia is attributed to a combination of factors that disturb the integrity and function of the AV conduction tissue, including:

• Direct surgical trauma
  • Incision, suturing, or manipulation near the AV node and BH can result in conduction tissue injury.
• Ischemia
  • Interrupting the blood supply during surgery may promote ectopic activity by inducing cellular injury in conduction tissues.
• Inflammation and edema
  • Postoperative inflammation can irritate the AV node region, increasing automaticity.
• Mechanical stretching
  • Anatomical repositioning or hemodynamic changes can stretch conduction fibers, altering their electrophysiologic properties.
• Catecholamine surge
  • Increased sympathetic stimulation postoperatively, often exacerbated by inotropic agents, lowers the threshold for arrhythmogenesis.
• Electrolyte imbalances
  • Hypokalemia, hypomagnesemia, and acidosis are known to potentiate conduction disturbances.

Several risk factors further increase the likelihood of developing POJET:

• Postoperative use of inotropes, particularly dopamine and milrinone
• Higher postoperative core temperatures
• Electrolyte abnormalities (eg, hypokalemia, hypomagnesemia)
• Age less than 6 months
• Prolonged duration of surgery
• Type of congenital defect and surgical procedure performed [2][3][4]

Procedures associated with a higher incidence of POJET include repairs of tetralogy of Fallot, ventricular septal defect (VSD), atrioventricular septal defect (AVSD), and arterial switch operations. The more complex the surgical repair, particularly those involving structures near the AV node, the higher the risk of POJET.

Epidemiology

JET is a relatively uncommon arrhythmia in the pediatric population, with distinct patterns based on whether it is CJET or POJET. CJET is extremely rare; long-term data collected over 40 years from major electrophysiology centers have reported only about 100 cases worldwide.[1] CJET typically presents within the first 6 months of life, often at birth, and shows a slight male predominance in some series. Despite its rarity, CJET carries a high burden of morbidity and mortality, with reported mortality rates up to 30% to 35% if not diagnosed early and appropriately treated. This type is frequently refractory to standard medical therapy and can lead to tachycardia-induced cardiomyopathy or congestive heart failure if persistent.

POJET is encountered more commonly in pediatric cardiac intensive care units and has been documented in up to 5% of children following cardiac surgery.[5] The incidence of POJET can vary depending on the complexity and nature of the surgical repair, especially procedures that involve structures close to the AV node and conduction tissues, such as repairs of:

• Tetralogy of Fallot
• VSD
• AVSD
• Arterial switch operation
• Double outlet right ventricle (DORV) corrections

Risk factors associated with a higher incidence of POJET include age younger than 6 months, prolonged cardiopulmonary bypass time, postoperative use of inotropes (such as dopamine and milrinone), higher postoperative core temperatures, electrolyte imbalances, and longer surgical durations. Although POJET often resolves spontaneously within 5 to 7 days after surgery, its occurrence is associated with important clinical consequences, including hemodynamic compromise, prolonged mechanical ventilation, increased intensive care unit length of stay, and, in some instances, increased postoperative mortality.

Pathophysiology

JET is primarily driven by enhanced and abnormal automaticity from the AV junction, including the AV node and proximal His bundle. JET does not involve a reentrant circuit, unlike reentrant arrhythmias such as AVNRT and AVRT. Instead, it results from spontaneous, pathological depolarizations within the AV conduction tissue, leading to rapid and often incessant tachycardia. This mechanism also explains why JET is refractory to treatments that typically target reentrant arrhythmias, such as intravenous adenosine and direct current cardioversion.

In CJET, intrinsic abnormalities of the conduction tissue are suspected. Genetic factors have been implicated, with proposed associations including deletions and mutations involving the angiotensin-converting enzyme insertion/deletion (ACE I/D) polymorphism and the troponin-I interacting kinase gene.[6] The latter has been particularly associated with the development of dilated cardiomyopathy in patients with congenital JET, indicating a broader myocardial dysfunction beyond arrhythmogenesis.[7]

In POJET, the pathophysiology is often multifactorial, typically precipitated by direct surgical trauma, ischemia, edema, or inflammation affecting the AV node and its surrounding tissues during the repair of congenital heart defects. Postoperative factors such as elevated catecholamines, hyperthermia, electrolyte disturbances, and the use of inotropic agents like dopamine and milrinone further enhance automaticity within the AV junction. The resulting tachycardia can be regular or irregular and is often characterized by AV dissociation or a 1:1 ventriculoatrial conduction pattern. Clinically, the high ventricular rates associated with JET significantly reduce diastolic filling time, compromising stroke volume and cardiac output, which can lead to profound hemodynamic instability, particularly in neonates and young infants with limited cardiac reserve.

History and Physical

The clinical presentation of JET varies depending on whether it is CJET or POJET; however, signs of tachycardia-induced hemodynamic compromise are common in both forms.

History

• CJET
  • CJET usually occurs in infants younger than 6 months old, although diagnosis can sometimes be delayed beyond that age. Prenatally, fetal tachycardia may be noted on routine fetal monitoring, and in severe cases, may present as fetal congestive heart failure or hydrops fetalis.[8] After birth, parents may report nonspecific symptoms such as poor feeding, irritability, tachypnea, diaphoresis, failure to thrive, or signs suggestive of heart failure. Infants typically have persistent tachycardia, with heart rates ranging from 200 to 250 beats per minute. More severe presentations include dilated cardiomyopathy, ventricular fibrillation, and even complete heart block leading to sudden cardiac death.[9] 
  • Historically, mortality rates for CJET have been reported as high as 35%, although more recent data suggest a lower mortality rate between 4% and 9%. Younger infants tend to experience more incessant tachycardia compared to older infants, correlating with a higher risk of mortality. Clinically, CJET characteristically exhibits a gradual onset of tachycardia (referred to as the “warm-up phase”) and a gradual resolution (“cooling-down phase”), with rate variability, distinguishing it from other sudden-onset arrhythmias, such as supraventricular tachycardia.
• POJET
  • POJET typically presents within the first 72 hours after surgical repair of congenital heart defects. This type often manifests as a rapid, regular tachycardia, which may be detected through telemetry monitoring or during evaluation for sudden hemodynamic deterioration. Symptoms may include hypotension, poor peripheral perfusion, low urine output, tachypnea, and signs of low cardiac output. In the postoperative setting, rapid diagnosis and management are crucial to avoid progression to multiorgan dysfunction or cardiac arrest.

Physical Examination

• Vital signs
  • Marked tachycardia, typically between 170 and 250 beats per minute
  • Hypotension, often secondary to impaired ventricular filling and decreased cardiac output
  • Tachypnea, with or without evidence of pulmonary congestion
• Cardiac exam
  • Rapid heart rate with either a regular or irregular rhythm on auscultation
  • Diminished heart sounds due to poor stroke volume
  • Presence of cannon “a” waves in the jugular venous pulse, especially if ventriculoatrial (VA) dissociation occurs
• Respiratory exam
  • Tachypnea may be present, sometimes accompanied by crackles (indicating pulmonary congestion)
• Other signs
  • Cool, clammy extremities indicate poor perfusion
  • Hepatomegaly in cases progressing to right heart failure
  • In severe presentations, signs of cardiogenic shock or cardiac arrest

Evaluation

The evaluation of suspected JET includes a detailed clinical assessment, electrocardiographic analysis, laboratory testing, and imaging studies. The primary objectives are to confirm the diagnosis, distinguish JET from other supraventricular arrhythmias, assess for hemodynamic compromise, and identify potentially reversible causes or complications.

Clinical Assessment

As previously detailed, a thorough history and physical examination are essential.

Electrocardiogram 

The electrocardiogram is central to the diagnosis:

• Rate
  • A narrow complex tachycardia is typically observed, with heart rates ranging between 200 and 250 beats per minute.
• P wave–QRS relationship
  • The rhythm may show intermittent VA dissociation with irregular ventricular rates. If there is 1:1 VA conduction, the atrial and ventricular rates are identical, making it challenging to differentiate from AVNRT or AVRT.
• Warm-up and cool-down phases
  • Characteristic gradual acceleration and deceleration of the tachycardia help distinguish JET from reentrant arrhythmias.
• Response to adenosine
  • Adenosine does not terminate JET but may induce VA dissociation, revealing atrial nonparticipation in the tachycardia and helping distinguish it from AVNRT or AVRT.

In rare cases, patients may exhibit both JET and complete heart block, complicating diagnosis and management.

Laboratory and Ancillary Testing

• Serum electrolytes
  • Potassium, magnesium, and calcium levels should be checked and corrected, as imbalances can exacerbate arrhythmias.
• Arterial blood gases and serum lactate
  • Evaluate for acidosis and tissue hypoperfusion, especially in hemodynamically unstable patients.
• Thyroid function testing
  • Consider this testing in infants or older children with persistent arrhythmia without an obvious surgical trigger.
• Cardiac biomarkers
• Troponin may be elevated postoperatively or in the setting of myocardial injury.

Imaging Studies

• Chest x-ray
  • This is performed to assess for cardiomegaly or pulmonary edema, especially in cases presenting with heart failure.
• Echocardiography
  • This test is crucial for evaluating cardiac anatomy and function. In CJET, echocardiography often reveals cardiac dilation and systolic dysfunction secondary to tachycardia-induced cardiomyopathy. In the postoperative setting, it can help identify residual lesions, pericardial effusion, or valvular abnormalities.

Cardiac Monitoring and Telemetry

Continuous telemetry is useful for documenting arrhythmias, observing for VA dissociation, and assessing rate variability. This helps capture warm-up/cool-down phases, providing further evidence of JET.

Electrophysiology Study (EPS)

Reserved for refractory cases, an EPS can help localize the ectopic focus and differentiate JET from other supraventricular tachycardias. This is often performed when ablation is being considered, especially in older children or adolescents with drug-refractory CJET.

Genetic and Advanced Testing

In congenital cases, genetic evaluation may be considered, particularly if there is a coexisting cardiomyopathy or a strong family history of arrhythmias. Mutations in TNNI3K and ACE I/D polymorphisms have been associated with CJET and related cardiomyopathies.

Treatment / Management

Supportive Measures and Initial Stabilization

JET management begins with stabilizing the patient and addressing any contributing physiological derangements. Electrolyte abnormalities—particularly hypokalemia, hypomagnesemia, and hypocalcemia—should be promptly corrected, as they can trigger or sustain arrhythmias. Acid-base disturbances, such as metabolic acidosis, should also be corrected, as acidosis can impair myocardial function and exacerbate tachycardia. Adequate oxygenation and hemodynamic support are essential, especially in unstable patients. In cases of postoperative JET, minimizing the use of inotropic agents like dopamine and milrinone is prudent, as their use has been associated with increased arrhythmogenicity. Maintaining normothermia or inducing mild hypothermia postoperatively may also contribute to the control of arrhythmias.

Antiarrhythmic Therapy

Amiodarone is the cornerstone of pharmacologic therapy for both congenital and postoperative JET. This medication is typically initiated with a loading dose followed by a continuous maintenance infusion. Amiodarone may be used as monotherapy but is often combined with additional agents such as propranolol or flecainide, depending on patient tolerance and arrhythmia control.[10] The selection of combination therapy should be made cautiously, as multiple antiarrhythmic agents can increase the risk of proarrhythmia, including torsades de pointes and sudden cardiac death.(B2)

Adenosine is ineffective in terminating JET due to the lack of AV nodal reentry, although it may be used diagnostically to demonstrate VA dissociation. Ivabradine, which inhibits the If current in the sinus node, has shown promise in treating congenital JET, especially in cases where amiodarone is poorly tolerated or ineffective. This medication reduces automaticity without negatively impacting myocardial contractility or blood pressure, making it suitable for infants with compromised cardiac function. Other antiarrhythmics used with variable success in postoperative JET include dexmedetomidine, propafenone, procainamide, and sotalol.

Nonpharmacologic Interventions

Therapeutic hypothermia is an effective adjunct to pharmacologic therapy in patients with postoperative JET. Mild hypothermia, targeting a core temperature of 34 °C to 35 °C, reduces myocardial oxygen consumption and suppresses abnormal automaticity in the AV junctional tissues. This approach is particularly beneficial in managing arrhythmias during the early postoperative period. Prophylactic administration of magnesium sulfate before surgery may also reduce the incidence of postoperative JET by stabilizing the cardiac membrane and decreasing susceptibility to triggered activity.

Sedation and mechanical ventilation may be necessary in severely ill postoperative patients to reduce sympathetic tone and cardiac metabolic demand. These supportive measures can provide a more favorable environment for antiarrhythmic therapies to work effectively. Catheter ablation is typically reserved for patients with congenital JET who fail maximal medical therapy. While potentially curative, ablation carries a high risk of damage to the AV node or BH, often necessitating permanent pacemaker placement if complete heart block occurs. Therefore, it is considered only in refractory or life-threatening cases where other therapies have been exhausted.

Special Considerations in Fetal and Neonatal JET

Fetal junctional ectopic tachycardia poses unique diagnostic and therapeutic challenges. The 2023 Heart Rhythm Society Expert Consensus Statement emphasizes the importance of early detection and management of fetal tachycardia to prevent complications, such as hydrops fetalis and in utero heart failure. Fetal echocardiography is crucial in monitoring the fetal heart rhythm, heart rate, and signs of hemodynamic compromise. Transplacental therapy with antiarrhythmic agents such as flecainide, sotalol, or amiodarone may be initiated depending on maternal and fetal tolerance, gestational age, and disease severity. A multidisciplinary approach involving pediatric cardiologists, maternal-fetal medicine specialists, and neonatologists is critical for optimizing outcomes in these high-risk pregnancies.

Differential Diagnosis

The differential diagnoses for JET include: 

• AVNRT
  • This usually responds to intravenous adenosine as opposed to JET, which is resistant to it, given that it is enhanced automatically as the underlying pathophysiologic mechanism.
• Pediatric atrial flutter
• Pediatric atrial ectopic tachycardia
• Accelerated junction rhythm
• Wolf Parkinson White syndrome
• Permanent junctional reciprocating tachycardia

Prognosis

The prognosis of JET varies considerably depending on whether the arrhythmia is congenital or postoperative, as well as the age of onset, the duration and severity of tachycardia, and the promptness of diagnosis and treatment. CJET is associated with a more guarded prognosis due to its typically incessant nature, high ventricular rates, and resistance to conventional antiarrhythmic therapy. Historically, CJET has been linked with mortality rates as high as 35%, especially in cases that are not diagnosed early or fail to respond to treatment.

The risk is highest in infants younger than 6 months of age, where the rapid and persistent tachycardia often leads to tachycardia-induced cardiomyopathy, congestive heart failure, or sudden cardiac death. However, advances in diagnosis, earlier therapeutic interventions, and the availability of more effective antiarrhythmic medications such as amiodarone and ivabradine have significantly improved outcomes. Recent study results suggest that mortality rates for CJET have declined to approximately 4% to 9%, particularly in centers with specialized electrophysiology expertise.

POJET, in contrast, tends to have a more favorable prognosis. This condition usually occurs within 72 hours of cardiac surgery, particularly after repair of congenital heart defects, and is often transient. With appropriate supportive care, electrolyte correction, and pharmacologic treatment—most commonly with amiodarone or other antiarrhythmics—POJET generally resolves within a few days. The incidence of long-term sequelae such as persistent arrhythmia or heart failure is low when JET is promptly recognized and treated. That said, hemodynamic instability during episodes of POJET can still contribute to postoperative morbidity, including prolonged intensive care unit stay and increased need for mechanical circulatory support.

Patients with JET—especially congenital forms—require close follow-up. Long-term monitoring for recurrence, arrhythmia burden, ventricular function, and side effects from antiarrhythmic drugs is essential. In rare cases, catheter ablation or pacemaker implantation may be necessary in those with refractory arrhythmia or conduction system complications. Multidisciplinary care involving pediatric cardiology, electrophysiology, and critical care is key to optimizing both short-term outcomes and long-term quality of life.

Complications

JET, particularly CJET, can lead to a range of serious complications due to its rapid, often incessant nature and resistance to standard therapies. One of the most significant complications is tachycardia-induced cardiomyopathy, where persistent high heart rates impair ventricular function, resulting in left ventricular dilation and systolic dysfunction. This can progress to congestive heart failure if not promptly treated, presenting as poor feeding, dyspnea, hepatomegaly, and failure to thrive in infants. Another major complication, particularly in fetal or neonatal cases, is the development of hydrops fetalis due to sustained intrauterine tachycardia. Fetal JET may present with fetal tachycardia, cardiomegaly, pericardial effusion, and ascites, which are signs of impending decompensation and can lead to intrauterine demise if unrecognized.

In both CJET and POJET, ventricular fibrillation, sudden cardiac death, and complete heart block have been reported. The risk is heightened in infants younger than 6 months and in those with high arrhythmia burden or coexisting structural heart disease. Proarrhythmic effects of antiarrhythmic medications, particularly when used in combination or without appropriate monitoring, can also contribute to life-threatening arrhythmias.

In POJET, complications include hemodynamic instability, prolonged mechanical ventilation, extended intensive care unit stays, and increased morbidity due to low cardiac output or poor organ perfusion. The arrhythmia itself may also obscure signs of surgical complications or residual lesions, potentially delaying diagnosis and appropriate intervention. Finally, neurologic complications from poor perfusion during sustained tachycardia, especially in infants with low cardiac reserve, may result in long-term developmental delays or cognitive impairments.