Cardiac Arrest in an 8-Year-Old

An 8-year-old previously healthy male was brought to the Emergency Department (ED) by Emergency Medical Services (EMS) after he collapsed at home. Parents reported that he was in the pool and looked unwell. As he got out of the pool and started running toward the house, he suddenly fell to the ground. His mother, a nursing student, noted that he was pulseless and started cardiopulmonary resuscitation (CPR). When EMS arrived, he was obtunded, but had palpable pulses. In the ambulance, he was initially bradycardic, then developed a wide-complex tachycardia. A blood pressure was difficult to obtain.

On arrival to the ED, the patient was initially moving spontaneously. He had 2+ radial pulses bilaterally. His mental status quickly declined as he again became obtunded. Pulse oximetry was difficult to obtain. He received 4 rounds of CPR for pulseless electrical activity with momentary return of pulses each time. A limited bedside echocardiogram revealed severely decreased left ventricular systolic function. His electrocardiogram (ECG) is seen in Image 1.

Image 1

Figure 1
Image 1: ECG on arrival to the ED showed normal sinus rhythm, left axis deviation, diffuse ST segment depressions and ST elevations seen in aVR and V1.

This patient was cannulated onto venoarterial extracorporeal membrane oxygenation (VA-ECMO) in the ED and transferred to the pediatric intensive care unit (PICU). Upon arrival to the PICU, he was found to be in ventricular fibrillation consistent with torsades de pointes (Image 2) and was successfully cardioverted to sinus rhythm.

Image 2

Figure 2
Image 2: Rhythm strip from the PICU showing torsades de pointes prior to and following cardioversion.

Repeat ECG in the PICU while on VA-ECMO demonstrated resolution of ST changes and prolonged QTc of approximately 520msec (Image 3).

Image 3

Figure 3
Image 3: ECG several hours after presentation, patient on ECMO: normal sinus rhythm with prolonged QTc interval (~520 ms).

His parents denied any preceding fever, congestion, myalgias, shortness of breath, vomiting or diarrhea. He had no known ingestions.

The most likely etiology of this patient's clinical course and cardiac arrest is:

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