Innervation of the Human Atrioventricular Node via the Inferior Pyramidal Space: Characterization Using...

Area of Science:

• Cardiovascular Anatomy
• Autonomic Nervous System Research
• Cardiac Electrophysiology

Background:

• The inferior pyramidal space (IPS), an epicardial fat depot, is located at the inferior crux of the heart.
• The atrioventricular node (AVN), critical for cardiac conduction, resides at the apex of the IPS.
• The precise autonomic innervation of the human AVN via the IPS is not well understood.

Purpose of the Study:

• To investigate the detailed anatomical distribution and characteristics of autonomic nerve fibers and ganglia within the human inferior pyramidal space (IPS) surrounding the atrioventricular node (AVN).
• To elucidate the specific pathways and types of innervation (sympathetic and nonsympathetic) supplying the human AVN through the IPS.
• To establish a foundation for understanding the role of IPS neural structures in AVN function and potential therapeutic interventions.

Main Methods:

• Utilized seven whole-mount human heart samples containing the IPS and AVN, sourced from donor hearts unsuitable for transplantation.
• Dissected the IPS into anterior and posterior fat pads relative to the coronary sinus.
• Employed a whole-mount tissue-clearing technique combined with immunohistochemical staining to identify and quantify nerve fascicles and ganglia.

Main Results:

• Identified distinct patterns of sympathetic and nonsympathetic nerve fascicle distribution within the anterior and posterior fat pads of the IPS.
• Observed that sympathetic nerve fascicles were significantly thicker than nonsympathetic ones.
• Found a higher prevalence of predominantly nonsympathetic ganglia in the posterior fat pad compared to the anterior portion; AVN core regions showed fine nerve fiber networks but lacked thick fascicles or ganglia.

Conclusions:

• The human inferior pyramidal space (IPS) demonstrates a unique arrangement of autonomic innervation and ganglia surrounding the atrioventricular node (AVN).
• These neural elements within the IPS are likely crucial for the physiological regulation of AVN function.
• The identified neural structures represent a potential novel target for neuromodulation therapies aimed at correcting abnormal AVN function and heart rhythm disturbances.