Apnea mediated transient complete atrioventricular block in a pre-term neonate

We present a previously unrecognized, reversible cause for complete atrioventricular block in the sick neonate. An 18 day old 33 weeker with Tetralogy of Fallot was admitted with sinus rhythm on ECG. Soon after, the baby developed episodes of apnea during which ECG showed complete atrioventricular block. This was unresponsive to atropine and isoprenaline, and heart rate continued to deteriorate. Mechanical ventilation was initiated in view of the critical condition and in preparation for an emergency temporary pacing wire insertion. Remarkably, ventilation restored sinus rhythm. The probable mechanisms by which apnea and acute hypoxia can cause atrioventricular block include carotid chemoreceptor mediated reflex vagal stimulation, depression of atrioventricular nodal conduction, and increase in endogenous adenosine levels. It is prudent to consider this reversible mechanism in the differential diagnosis of new onset atrioventricular block in the sick neonate, as early recognition may help avoid unnecessary invasive interventions.