Histological observation of the cardiac conduction system in the diagnostics of sudden unexpected infant death (SIDS)

Introduction. The sudden infant death syndrome (SIDS) cases do not present any abnormality of the ordinary myocardium, while the core of the heart, where cardiac rhythm arises and spreads, can be abnormal, representing an insight to the solution of the problem. Material and Methods. To examine the cardiac conduction system, two blocks for paraffin embedding are prepared. The first block contains the junction of superior vena cava and right atrium encompassing the entire area of the sinus nod+e. The second block contains the atrio-ventricular node, His bundle down to bifurcation and bundle branches. The serial section is a must in conduction system investigation. Results Areas of resorptive degeneration were detected in 97% of the SIDS cases and in 76% of controls. The accessory pathways were mainly Mahaim fibers, detected in 22.5% of SIDS and in 8% of controls. Dispersion or septation of the atrio-ventricular node and/or His bundle, was observed in 41% of SIDS cases and in 16% of control cases. Cartilaginous meta-hyperplasia of the central fibrous body was present in 6% of SIDS and in 4% of controls. Dualism of the atrio-ventricular node and/or His bundle was present in 3% of our SIDS cases, and absent in controls. Discussion Frequent alterations are the accessory atrio-ventricular pathways, mainly of Mahaim type. These fibers can play an important role as pathogenic backgrounds of a significant number of cardio-arrhythmogenic SIDS.