Cardiac atrioventricular junctional tissues in hearts from infants who died suddenly.

The cause of sudden infant death syndrome is not known at present. Most agree that in the majority of cases it involves primary apnea. However, cardiac abnormalities probably account for a subset of these deaths. An investigation into the structure of the atrioventricular (AV) junctional tissues of the heart would provide insight into the frequency of sudden death in infants that might result from abnormal cardiac morphology. The hearts of seven infants who died from diagnosed sudden infant death syndrome were examined by serially sectioning and studying this critical region of the heart. The hearts of these infants could be divided into three groups on the basis of their morphologic features. In the first group, represented by two cases, there were marked variations from normal, the most striking feature being the presence of accessory pathways. In the second group, represented by four cases, the AV junctional tissues were not fully mature and clusters of AV nodal and bundle cells were dispersed throughout the anulus fibrosus. In the third group, the structure of the junctional tissues was normal. There remains a distinct subset of infants who might have died suddenly and unexpectedly from cardiac abnormalities that needs to be more completely defined.