[A histologic study on "surgical landmarks" of the specialized conduction system, with particular reference to the adjacent structure].

The conduction system in 29 cardiac specimens was histologically investigated as to the course and its surgical landmarks. The course varied individually, but was relatively inherent to the type of ventricular septal defect (VSD) (classification by Soto, et al.). The His bundle distributed as reported hitherto. Interesting features were noted in the relationship between the right bundle branch (RBB) and its adjacent papillary muscles. Our definition used for certain papillary muscles is merely to point the topographic site. The RBB ran beneath or slightly anterior to upper accessory papillary muscles (AcPMs) or uppermost AcPM, regardless of the type of perimembranous VSD. It ran posterior to the medial papillary muscle (MPM), with wider variation. In tetralogy of Fallot (TOF), it ran beneath or slightly anterior to the MPM. Relationships described above may be unitarily expressed as below, providing that Van Mierop's embryologic hypothesis on the conus defect anomaly (i.e.,: the uppermost AcPM being often morphologically interpreted as the MPM) is valid: -"The RBB runs beneath or slightly anterior to the upper(most) AcPM, regardless of the type of VSD. Such an arrangement was often observed in other anomalies too. The relationship between the RBB and upper or uppermost AcPM was modified by the attitude of the trabecula septomarginalis. Informations thus obtained have significantly lowered conduction disturbances in our experience.