Postoperative JET (PO-JET) is the most common form of an abnormal automatic rhythm in children. The exact mechanism for this arrhythmia is unknown; however, the fluid and electrolyte shifts of the early postoperative state, trauma, stretch, local edema, or ischemia in the region of the AV node and/or His bundle are likely candidates. Similar to the non-postoperative forms of junctional tachycardia, PO-JET is an automatic arrhythmia displaying warm-up and cool-down transitions to sinus rhythm. The onset is typically during the first 72 h post-op and in the great majority of patients, during the first 24 h. The heart rate during PO-JET can range from 150 to 240 bpm, potentially compromising cardiac output (Fig. 11.4). The atria and ventricles are activated nearly simultaneously from impulses originating within the His bundle causing the contraction of the atria against closed atrioventricular valves (Fig. 11.5). This lack of atrioventricular synchrony compromises the cardiac output by decreasing ventricular filling. Uncontrolled, this tachycardia may further lead to a fall in blood pressure, initiating a downward spiral characterized by increased endogenous catecholamines and increased inotropic support to maintain adequate blood pressure and renal perfusion. As a result of vasoconstriction, the patient’s skin may feel cool, but the core temperature rises because of an inability to dissipate heat. This increase in endogenous and exogenous adrenergic input as well as the elevation in core temperature exacerbates the tachycardia. Thus, it is critical to interrupt this cycle of escalating heart rate, increasing vasoconstriction, and falling cardiac output. Although postoperative JET is often self-limited, slowing to a tolerable heart rate within 48 h, rapid rates (≥180–190 bpm) associated with decreasing blood pressure require intervention. The slower rates often do not need treatment or only need atrial pacing at a slightly higher rate than the junctional rate to provide atrial-ventricular synchrony, and they rarely persist beyond 5–7 days.

The natural history of postoperative JET is time-dependent resolution, regardless of treatment, usually within 24–48 h. Early reports cited up to a 16% mortality. More recently with improved understanding and treatment, a fatal outcome is now uncommon, though there is an increased risk of perioperative death in patients experiencing JET compared to those without JET.

Many studies over the past two decades have attempted to establish the incidence and risks of developing postoperative JET. The reported incidence of JET varies widely from 1.4 to 15 % when all open cardiac operations for congenital malformations are considered. However, a number of lesions are the predominate ones at risk, including tetralogy of Fallot (14–37 %), repair of anomalous pulmonary venous return (36 %), arterial switch operation (23 %), atrioventricular canal (10–21 %), Norwood procedure (20 %), and interrupted aortic arch repair (17 %). Even Blalock–Taussig shunt placement has been reported to result in PO-JET, despite the fact that no intracardiac manipulation is performed. Other risk factors are longer duration of cardiopulmonary bypass, longer aortic cross clamp time, patient temperature, and elevated biomarkers of cardiac injury. Inotrope use, especially dopamine and milrinone, have been correlated to higher risk of JET. Specific genetic polymorphisms, such as the angiotensin-converting enzyme insertion/deletion polymorphism also appear to predispose to JET.

The wide variation in incidence is likely dependent on multiple factors, including an era effect and different center practices. One major cause of variation is the lack of a standard definition of JET across these studies. Early studies on PO-JET differentiated it from other tachyarrhythmias by failure of overdrive pacing or DC cardioversion. Even today the precise definition of JET remains unclear—either exclusively having VA dissociation or inclusive of both VA dissociated and 1:1 conducting arrhythmias provided the tachycardia is diagnosed “JET” in the patient’s medical record. The former criteria will underdiagnose those patients who conduct 1:1 retrograde consistently during JET. The latter interpretation will overdiagnose JET, including other normal complex QRS tachycardias with 1:1 conduction and simultaneous VA or short VA conduction. Visualization of the onset or offset of the tachycardia or other diagnostic maneuvers (overdrive pacing, adenosine) is necessary for a completely accurate diagnosis.

The treatment of postoperative JET has evolved over the past two decades. The initial steps are reduction of catecholaminergic stimuli along with, hypothermia, atrial pacing, antiarrhythmic medications, and time.

Hypothermia induction to 32–34° using extracorporeal cooling or intravenous cooling is effective for slowing the rate. This strategy is also used to allow atrial pacing at 10–20 bpm above the JET rate, thereby restoring atrioventricular synchrony. The JET rate typically needs to be <180 bpm to successfully overdrive the rhythm. This goal can also be achieved with antiarrhythmic medications.

Nearly all intravenous antiarrhythmic medications have been evaluated as therapy for PO-JET. The earliest studies showed that digoxin has some effect, but beta-blockers, phenytoin, and calcium channel blockers were found to be relatively ineffective and carried an increased risk of complication due to their negative inotropic effects. The class IC antiarrhythmics, flecainide, and propafenone have been the subjects of favorable reports in small single center studies. Importantly, procainamide reduces JET rates in a dose-dependent manner. Despite the demonstration of efficacy and the absence of side effects in these prospective studies, procainamide may lead to significant causing hypotension secondary to sympathetic ganglion blockade.

Amiodarone is the most widely studied antiarrhythmic for the treatment of PO-JET. It appears most efficacious when administered as 1 or 2 loading doses of 5 mg/kg followed by a continuous infusion. A double-blind randomized controlled drug trial evaluated the efficacy of three different amiodarone dosing strategies on incessant tachyarrhythmias in pediatrics. While a dose-dependent time to effect was found for the entire dosing level cohorts, JET as a subgroup did not show significant difference in efficacy across dosing levels cohort. The study also found a dose-dependent risk of side effects: 36 % of patients experienced hypotension (undefined); 20 %, bradycardia (undefined); and 15 %, atrioventricular conduction block. Amiodarone has also been used prophylactically after tetralogy of Fallot repair as a 48 h continuous infusion (2 mg/kg/day) with a decrease in the occurrence of JET (10 %) as compared to a control group (37 %). It is important to remember the high incidence of acute, chronic, and potentially severe side effects of amiodarone when considering it as a treatment strategy for this self-limited arrhythmia.

Many centers employ a staged treatment protocol to address PO-JET, utilizing a sequential combination of treatments. Initial interventions include reduction of inotropic support and catecholaminergic stimuli, if possible, including sedation and paralysis. Cooling followed by active cooling and antiarrhythmic medications are instituted subsequently. Atrial pacing above the JET rate should be considered at any stage. The rapidity that one moves through the levels of treatment is dependent on the patient’s clinical status and response to intervention. Because PO-JET is a transient arrhythmia, it is important to weigh the use of treatment with the clinical need. Stable PO-JET, without significant hemodynamic consequence, can be treated solely by removal of stimuli, cooling, and patience.

Congenital JET is rare. A review of all non-postoperative JET patients from 22 centers over 40 years identified just 44 patients with tachycardia at 6 months or less. Maternal and neonatal risk factors are unclear due to the rarity of the diagnosis. Fetal tachycardia was found in 36 % of the congenital JET population and an association with family history of JET and minor congenital heart defects was noted. The influence of maternal auto-antibodies is unknown.