Histopathology of the conduction system in sudden infant death

Because ventricular fibrillation or other arrhythmia have been suggested as a cause of unexplained sudden infant death, many authors focused their studies on the conduction system especially in the 1970s. These studies were not conclusive and many pathologists have abandoned the study of the conduction system. We have reviewed the conduction system of 87 sudden infant death cases between 15 days and 1 year old: 55 were SIDS cases; 17 had mild lesions insufficient to explain death and 15 cases were sudden explained deaths considered as controls. Fetal dispersion of the AV node and/or His bundle and left-sided His bundle, the most frequent findings in the three groups, can be considered normal variations. Nodoventricular tracts were observed in five cases from the three groups whereas fasciculoventricular tracts were present in seven cases of the SIDS group, one case of the second group and in no controls. We consider the possible pathologic significance of this accessory pathway in some SIDS cases. Other infrequent lesions were fibromuscular hyperplasia of AV node artery and His bundle hemorrhage in one SIDS case each; lymphocytic infiltration of the conduction system in one SIDS case and one case with myocarditis and left bundle branch fibrosis in a female infant with endocardial fibroelastosis.