| Description |
The cardiac conduction system is a specialized network of tissue throughout the heart that initiates and propagates electrical excitation signals which allow the heart to beat in a synchronous manner. Principal elements of the cardiac conduction system include the sinoatrial node, atrioventricular node, His bundle, left and right bundle branches, and Purkinje fibers. For years, surgeons and researchers have sought an effective method to localize these structures in procedures. Success and effectiveness of cardiac procedures like repair of critical congenital defects, right atrium and atrioventricular node ablation, and His bundle pacing depend on reliable localization of these structures. Inadvertent trauma to the cardiac conduction system leads to high levels of morbidity and mortality. Fiber-optic confocal microscopy has shown promise in locating the sinoatrial and atrioventricular nodes, but it has yet to be validated in larger mammalian hearts. This work aims to provide surgeons and researchers with a geometrical analysis of the sinoatrial and atrioventricular nodes in human and ovine hearts that will aid in the development and validation of localization devices. Through the analysis of hundreds of high-resolution serial histology images, we examined the depth, structure, microstructure, and adjacent environment of the sinoatrial and atrioventricular nodes. We utilized Masson's trichrome-stained sections along with segmentation and image processing programs designed to analyze these complex geometries. We found that the sinoatrial node resides on the right atrium epicardial surface with an average minimum depth of 55.6 μm, and the iv atrioventricular node resides beneath the right atrium endocardial surface with an average minimum depth of 171.4 μm. The depth of the atrioventricular node in ovine and human hearts increases logarithmically with age. We also reveal that the composition and microstructure of tissue superficial to the atrioventricular node can be used for reliable localization of deeper nodal structures. |
