The Conduction System
Histologic examination of the conduction system is difficult and time-consuming, and it is usually fruitless unless the patient has a clinical history of a complete heart block. Nonetheless, in some in-stances examination of the conduction system can provide critical insight into the underlying nature of the patient’s pathology.
In general, the sinoatrial node is not present in the explanted heart. Examination of the atrio-ventricular (AV) node was well described by Hutchins:3 From the right side of the heart, iden-tify the ostium of the coronary sinus, the septal leaflet of the tricuspid valve, the membranous interventricular septum, and a line approxi-mately 2 cm below the insertion of the septal leaflet of the tricuspid valve. Remove the block of tissue contained within these landmarks by cutting into the septum from the right side. This block of tissue can then be serially sectioned for histologic examination.