Electrocardiac responses associated with the fear paralysis reflex in infant rabbits and rats. Relation to sudden infant death.

It is a controversial issue whether non-hereditary prolonged cardiac repolarization (increased QT-interval in ECG) is a cause of sudden infant death syndrome (SIDS). The QT-interval has, however, been found to be normal at rest. The present experiments on infant rats and infant and adult rabbits demonstrate a transient QT-prolongation during the innate fear paralysis reflex elicited by a variety of frightening stimuli. This reflex has previously been proposed as a triggering mechanism for SIDS. It may represent an extrinsic cause of QT-prolongation which adds to an intrinsic defect in repolarization previously reported. The present findings lend further support to the fear paralysis theory of SIDS.