Author: Melissa Colizza, MD - Stollery Children’s Hospital - Edmonton, Canada
A 3-month-old infant has just undergone ventricular septal defect closure on cardiopulmonary bypass. After weaning from bypass, the rhythm strip demonstrates a narrow-complex tachycardia at a rate of 190 bpm. The CVP tracing demonstrates a large V wave and absent A wave, and transesophageal echocardiography reveals depressed left ventricular function. Which of the following treatments is MOST appropriate for management of this rhythm?
EXPLANATION
Junctional ectopic tachycardia (JET) is a relatively common tachyarrhythmia occurring after congenital cardiac surgery with a reported incidence of 1 to 10%. It is caused by enhanced automaticity of the atrio-ventricular (AV) node at ventricular rates greater than or equal to 160 to 170 bpm. It is characterized by a narrow QRS complex with either ventriculo-atrial (VA) dissociation or 1:1 retrograde conduction (retrograde P-waves). The etiology remains unclear but is hypothesized to result from direct mechanical trauma or indirect stretch injury to the conduction system. Risk factors include specific surgical procedures (Tetralogy of Fallot repair, ventricular septal defect closure, and atrio-ventricular septal defect repair), young age, heterotaxy syndrome and prolonged cross-clamp time. The clinical impact of JET is significant as the loss of AV synchrony often results in a decrease in cardiac output, potentially leading to prolonged intubation and hospitalization.
Management principles of JET in the post-bypass period are based on decreasing the adrenergic drive that sustains tachycardia, controlling heart rate and re-establishing AV synchrony. General measures include the following: 1) cooling to 33-35oC; 2) decreasing the dosage of or eliminating sympathomimetic drugs; and 3) correcting electrolyte abnormalities, in particular calcium, magnesium, and potassium. Overdrive pacing involves temporarily pacing the heart at a rate that is 10-20 bpm over the underlying rate in order change the refractory period and terminate the tachyarrhythmia. It is less effective for termination of automatic tachyarrhythmias versus re-entrant tachyarrhythmias. Additionally, when the native rate is greater than 180-190 bpm, overdrive pacing may be detrimental, as the even faster heart rate would limit cardiac filling, decrease cardiac output, and cause significant hypotension.
Amiodarone is a class III anti-arrhythmic agent with multiple mechanisms of action including the following, 1) inhibition of fast sodium channels; 2) depression of sinus node automaticity and AV nodal conduction; and 3) prolongation of the refractory period secondary potassium channels. Its use has been described in both the prevention and treatment of JET. Treatment proceeds with a loading dose of 5-10 mg/kg over 30-60 minutes and an infusion of 5-15 mg/kg/day. Adverse events may include hypotension, bradycardia, AV block and rarely, cardiovascular collapse due to calcium chelation.
Procainamide is a class I anti-arrhythmic drug, which acts predominantly on sodium channels. It has a shorter onset of action and half-life than amiodarone. Clinical efficacy is increased when used in conjunction with core temperature cooling. However, decreased systemic vascular resistance and inotropy occur more frequently with procainamide than amiodarone, making use of this drug less appropriate in patients with concurrently depressed ventricular function. Usual dosing includes a loading dose of 10-15 mg/kg over 30-45 minutes and an infusion rate of 40-50 mcg/kg/min.
Other agents are used for both prophylaxis and treatment of JET. Multiple studies have demonstrated that prophylactic dexmedetomidine, a selective a2-agonist used for sedation, is effective at preventing JET when an infusion is started pre-incision and continued postoperatively. A prospective, randomized placebo-controlled study by El Amrousy et al demonstrated that a loading dose of dexmedetomidine of 0.5 mcg/kg followed by a continuous infusion at 0.5 mcg/kg/h for 48 hours postoperatively significantly reduced the incidence of JET to 3.3% versus 16.7% in the placebo group. The study group also had a reduction in mechanical ventilation time, duration of ICU stay, and hospital length of stay. However, there was no difference in mortality rate, nor the incidence of bradycardia and/or hypotension between the two groups. Magnesium sulfate has also shown promising utility for prophylaxis of JET in the pediatric population. A 2022 meta-analysis by Mendel et al compared the efficacy of dexmedetomidine, magnesium and amiodarone for JET prophylaxis. Although all three drugs were effective at preventing JET,only amiodarone and dexmedetomidine decreased ICU length of stay. Further, only dexmedetomidine was associated with decreased mortality. The authors concluded that dexmedetomidine may be the drug of choice for preventing JET. Other drugs used to treat JET include digoxin and sotalol, albeit with little supportive data. Ivabradine, an oral medication, is being utilized with increasing frequency as a novel treatment of postoperative JET. In a small study by Kumar et al, it was demonstrated to be effective at reducing heart rate and converting JET to sinus rhythm in five patients who were refractory to amiodarone treatment. Ivabradine is orally administered and reaches peak plasma concentration in one hour, limiting its use for terminating JET in the immediate post-bypass period.
The correct answer in this clinical scenario is amiodarone for the treatment of JET, which is demonstrated with findings on the rhythm strip and CVP tracing described in the stem. Procainamide would not be appropriate to treat JET in a patient with depressed ventricular function. No treatment is not the correct answer as JET can lead to hemodynamic instability and cardiac arrest. Overdrive pacing would have limited utility as this patient’s heart rate is already quite high at 190 bpm and has a high likelihood of causing hypotension.
REFERENCES
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El Amrousy DM, Elshmaa NS, El-Kashlan M, et al. Efficacy of Prophylactic Dexmedetomidine in Preventing Postoperative Junctional Ectopic Tachycardia After Pediatric Cardiac Surgery. J Am Heart Assoc. 2017;6(3):e004780. doi: 10.1161/JAHA.116.004780
Mendel B, Christianto C, Setiawan M, Prakoso R, Siagian SN. A Comparative Effectiveness Systematic Review and Meta-analysis of Drugs for the Prophylaxis of Junctional Ectopic Tachycardia. Curr Cardiol Rev. 2022;18(1):e030621193817
He D, Sznycer-Taub N, Cheng Y, et al. Magnesium Lowers the Incidence of Postoperative Junctional Ectopic Tachycardia in Congenital Heart Surgical Patients: Is There a Relationship to Surgical Procedure Complexity? Pediatr Cardiol. 2015;36(6):1179-1185. doi: 10.1007/s00246-015-1141-5
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