7.4 Atrioventricular Septal Region

Atrioventricular Septal Region is the anatomical area within the heart that constitutes the complex interface between the atrial and ventricular chambers, specifically at the junction where the atrial septum, ventricular septum, and atrioventricular (AV) valves converge. This region includes the structural and fibrous elements that separate the right and left atrioventricular orifices, providing both mechanical support for the valves and electrical insulation between atria and ventricles. It plays a critical role in maintaining the integrity of cardiac septation and ensuring unidirectional blood flow through the AV valves during the cardiac cycle.

Structural Overview

The atrioventricular septal region encompasses multiple components that contribute to its complex architecture:

Atrioventricular Septal Position

This describes the spatial orientation of the atrioventricular septal region relative to adjacent cardiac structures. It lies between the right atrium and left ventricle, forming a three-dimensional interface where the fibrous skeleton of the heart connects the atrial and ventricular myocardium.

Atrial-Ventricular Septal Offset

A key characteristic of this region is the offset between the atrial and ventricular septa, resulting in the atrioventricular septal plane being obliquely oriented rather than a simple straight partition. This offset is important for the proper alignment of the mitral and tricuspid valve orifices and contributes to the septal architecture that accommodates the valves.

Right Atrial-Left Ventricular Adjacency

Uniquely, the atrioventricular septal region includes the anatomical adjacency where the right atrium lies in close proximity to the left ventricle due to the septal structure. This adjacency is significant in the conduction of electrical impulses and in certain congenital malformations where abnormal communication between chambers may occur.

Subregions of the Atrioventricular Septal Region

The atrioventricular septal region is further subdivided into superior, inferior, and central fibrous areas, each with distinct anatomical and functional relevance.

AV Septal Superior Region

Located near the atrial septum and the superior aspect of the atrioventricular junction, this region includes the fibrous continuity between the aortic and mitral valves and the superior rim of the atrioventricular septal area. It provides a structural connection that supports valve function and electrical insulation.

AV Septal Inferior Region

This region lies closer to the inferior margin of the atrioventricular septum adjacent to the membranous septum. It includes the inferior rim of the fibrous skeleton, contributing to the separation between the right and left sides of the heart at the base of the ventricles. It also contains parts of the fibrous trigones important for valve anchoring.

AV Septal Central Fibrous Interface

The central fibrous body is a dense fibrous structure at the core of the atrioventricular septal region. It forms the pivotal anchoring point for the mitral and tricuspid valves and includes the membranous septum. This interface is crucial for the transmission of forces during cardiac contraction and serves as a barrier to electrical conduction except at the atrioventricular node and bundle of His, which traverse this region.

Valve Relations within the Atrioventricular Septal Region

The atrioventricular septal region maintains intimate relations with both the mitral and tricuspid valves, facilitating their coordinated function.

AV Septal Mitral Relation

The mitral valve is connected to the atrioventricular septal region via fibrous continuity and the mitral annulus, which is partly formed by the central fibrous body. This relation influences the motion and competence of the mitral valve leaflets and ensures proper closure during ventricular systole.

AV Septal Tricuspid Relation

Similarly, the tricuspid valve has a close anatomical relationship with the atrioventricular septal region, especially near the membranous septum and fibrous trigones. This proximity allows coordinated valve function and contributes to the electrical insulation between atrium and ventricle except along the conduction system pathways.

AV Septal Membranous Relation

The membranous septum, a small but crucial fibrous partition, is embedded within the atrioventricular septal region. It separates the left ventricular outflow tract from the right atrium and right ventricle and is the site of important conduction tissue. Its integrity is essential for preventing pathological shunting and ensuring synchronized contraction.

Spatial Mapping and Functional Importance

Atrioventricular Septal Spatial Map

The spatial configuration of the atrioventricular septal region is three-dimensional and complex, incorporating the fibrous skeleton, muscular septa, valve leaflets, and conduction tissue. Mapping this region spatially helps in understanding congenital defects such as atrioventricular septal defects, arrhythmogenic substrates, and surgical approaches.

The atrioventricular septal region supports the mechanical function of the heart by anchoring valves and separating chambers, while simultaneously serving as a conduit and barrier for electrical impulses. Its balance of fibrous and muscular components ensures the heart’s efficiency and electrical stability.