Case 3: An Unusual Rhythm in a 12-day-old Infant

Presentation

A 12-day-old neonate born at 36 weeks and 2 days of gestation is transferred to an outside institution for further management of an arrhythmia noted in the early postnatal period. Before her transfer, she had been admitted to the NICU at another hospital for management of postnatal hypoglycemia. While her hypoglycemia was being managed, an irregular rhythm was appreciated on physical examination, prompting further evaluation. A monomorphic, wide QRS complex rhythm was captured on 12-lead electrocardiography (ECG). The infant was placed on continuous telemetry, which revealed frequent salvos of the wide QRS complex rhythm at rates slightly faster than baseline sinus rates. Echocardiography showed normal intracardiac anatomy, no evidence of significant pulmonary hypertension, and normal left ventricular systolic function during periods of sinus rhythm. Given the perceived high arrhythmia burden, propranolol was initiated and the patient was subsequently transferred to a different center.

Initial evaluation in the current NICU reveals a normal-appearing neonate with no significant abnormalities on physical examination. The infant feeds normally and appears to be in no distress. Telemetry shows intermittent salvos of a wide QRS complex rhythm, with abrupt onset and resolution. Serial ECGs record periods of sinus rhythm (Fig 1A) and nonsustained episodes of monomorphic wide QRS complex tachycardia at rates slightly faster than the preceding sinus rate (Fig 1B). These episodes occurred randomly and were generally brief, lasting less than 30 seconds.