Supraventricular Tachycardia as a First Sign of Inborn Metabolic Disease

Introduction: Supraventricular tachycardia (SVT) is the most common arrhythmia in children. SVT may manifest as self-limited paroxysm, or on the contrary as a prolonged dysrhythmia with the subsequent development of cardiac dysfunction, heart failure and multiple organ failure. Cardiac disease associated with an inborn metabolic disorder (IEM) can present as an immediate life-threatening pathology with symptoms affecting growth and development, or as a “silent” disease with an increased risk of sudden cardiac death.

Case Presentation: We report two cases of children who were initially admitted for supraventricular tachycardia, but who have been later diagnosed with an IEM.

Our first patient, a four months old infant, presented in the emergency department with irritability, inappetence and tachypnea. He was diagnosed with SVT and found to be hemodinamically unstable, so he required electrical conversion to sinus rhythm. The initial clinical and biological evaluation pointed towards cardiogenic shock and multiple organ failure. Echocardiography revealed the presence of eccentric hypertrophic cardiomyopathy. Acylcarnitine profile was also evaluated, indicating a low free carnitine level. Treatment with oral carnitine led to normal carnitine values at following visits and a good cardiologic outcome, without other SVT episodes.

Our second patient, of one year and two months, presented two episodes of SVT, at two months interval, both occurring during an infectious episode. Both episodes responded promptly to adenosine therapy. Echocardiography indicated a dilated left ventricle, with preserved systolic and diastolic functions. Shortly after the second episode, the patient presented another infectious episode with fever, vomiting and many loose stools, without cardiac rhythm disturbances associated. He presented in the emergency room, where the biological evaluation uncovered severe metabolic acidosis with an increased anion gap, which does not respond to classical rehydration therapy, revealing also ketonemia and increased ammoniemia. A spectroscopic MRI examination of his urine sample indicated high levels oh methyl-malonic acid, establishing the diagnosis of methyl-malonic acidemia, However, the patient died 44 hours after admission.

Discussion: The diagnosis of an IEM as a cause of cardiomyopathy is extremely important as there is often a specific treatment available for this disorders, highlighting also the importance of genetic counseling in this cases.