Histochemistry of the atrioventricular conducting system during postnatal development.

The atrioventricular conduction system of 27 infants coming to autopsy was examined by histochemical methods. Twenty one were sudden infant deaths; six were explained deaths. A decrease of oxidoreductases and hydrolases activities was found in clusters of conducting cells protruding from the atrioventricular (AV) node and His bundle left into the collagen of the septum. These findings reflect regressive changes connected with reduction of the AV conducting system during postnatal development.