A baby born at 37 weeks’ gestation was noted to have premature beats in utero. He was born in good condition. The premature beats were heard intermittently in the first few hours of life. There was no significant family history. He remained well with normal observations and was discharged home after reassurance was provided. At 9 days of age an irregular pulse was noted again during an assessment for jaundice.

On initial assessment, he appeared well. He had an irregular pulse but no other abnormalities in his cardiovascular examination. He required phototherapy for the jaundice. There were no electrolyte abnormalities.

His initial 12-lead electrocardiogram (ECG) showed sinus rhythm with frequent broad-complex beats. A 24-hour ECG (Holter) was performed (see figure 1).

3-lead monitoring from 24-hour Holter ECG monitor.

What is the mechanism of the rhythm shown in figure 1?

Ventricular tachycardia

Accelerated idioventricular rhythm

Sinus rhythm …