7.5 Interventricular Septum

Interventricular Septum is a thick, muscular wall that separates the left and right ventricles of the heart. It forms a crucial internal partition within the cardiac structure, preventing the mixing of oxygenated blood in the left ventricle with deoxygenated blood in the right ventricle, thereby maintaining efficient circulatory separation and cardiac function.

Structure and Composition

The interventricular septum is composed predominantly of cardiac muscle tissue (myocardium) and is divided into two distinct parts: the muscular septum and the membranous septum. The muscular portion constitutes the majority of its mass and provides the contractile force necessary for ventricular systole. The membranous septum is a thinner, fibrous part located near the base of the heart, adjacent to the atrioventricular septum, and plays a key role in the integrity of the cardiac conduction system.

The septum's thickness varies throughout its length, being thickest at the base near the atrioventricular valves and tapering towards the apex of the heart. Its three-dimensional form conforms closely to the shape of the ventricles, contributing to the overall conical architecture of the ventricular chambers.

Regional Divisions of the Interventricular Septum

Basal Interventricular Septal Region

The basal region lies closest to the atrioventricular valves and the cardiac base. It contains part of the membranous septum and contributes to the fibrous skeleton of the heart. This region is important for anchoring the cardiac valves and is a critical area for the conduction pathways, including the atrioventricular bundle.

Midventricular Septal Region

This is the central portion of the muscular septum, thicker than the basal region, and constitutes the bulk of the interventricular septum. It contains dense myocardial fibers arranged in a complex helical pattern, facilitating coordinated contraction during systole.

Apical Interventricular Septal Region

The apical region tapers down near the apex of the heart and is the thinnest portion of the septum. Despite its reduced thickness, it plays an important role in defining the ventricular apex and contributing to the ventricular free walls.

Surfaces and Orientation

Right Ventricular Septal Face

The right ventricular face of the interventricular septum is relatively smooth and convex, forming part of the right ventricular cavity. This surface is visible from inside the right ventricle and serves as the attachment site for the septal leaflet of the tricuspid valve. It is also the site where the right bundle branch of the conduction system runs.

Left Ventricular Septal Face

The left ventricular face is more irregular and slightly concave, contributing to the left ventricular cavity. It provides attachment points for the septal leaflet of the mitral valve apparatus and reflects the complex trabecular pattern characteristic of the left ventricle.

Position, Orientation, and Curvature

The interventricular septum lies obliquely between the ventricles, extending from the base of the heart near the atrioventricular junction towards the apex. Its orientation forms an angle with the long axis of the heart, accommodating the spatial arrangement of the right and left ventricles, which are offset both anteriorly and posteriorly.

The curvature of the septum is convex toward the right ventricle due to higher pressure in the left ventricle during systole. This convexity can vary with changes in intraventricular pressure gradients and is an important indicator in cardiac imaging and pathology.

Septal Free-Wall Junction

The interventricular septum meets the free walls of the right and left ventricles at the septal free-wall junctions. These junctions are crucial anatomical landmarks that mark the transition between the septal myocardium and the ventricular free walls. They contribute to the mechanical integrity of the ventricular chambers and serve as sites of insertion for myocardial fibers that coordinate ventricular contraction.

Three-Dimensional Form

The three-dimensional architecture of the interventricular septum is complex, reflecting its role as a dynamic structure in the heart. It is not a simple flat wall but exhibits curvature and variable thickness to accommodate the different pressures and mechanical demands of the right and left ventricles. It participates actively in the systolic contraction, contributing to the ejection of blood from both ventricles.

The septum also houses important components of the cardiac conduction system, including the bundle of His and its branches, which traverse the membranous and muscular parts, facilitating synchronized ventricular contraction.

The interventricular septum is a fundamental cardiac structure essential for the separation of the ventricles, mechanical support, and conduction of electrical impulses. Its anatomy and physiology are critical to maintaining the efficiency of cardiac function and systemic circulation.