5.11 Right Ventricular Outflow Tract

Right Ventricular Outflow Tract (RVOT) is the superior, smooth-walled portion of the right ventricle that leads to the pulmonary valve and pulmonary artery. It serves as the pathway for blood ejected from the right ventricle into the pulmonary circulation. The RVOT is a key anatomical and functional structure within the right heart, distinguished from the trabeculated inflow portion of the right ventricle by its smooth walls and distinct muscular boundaries.

Anatomical Definition and Boundaries

The RVOT, also known as the infundibulum or conus arteriosus, forms the outflow portion of the right ventricle and is located anteriorly and superiorly relative to the right ventricular inflow tract. It extends from the supraventricular crest—a muscular ridge separating the trabeculated right ventricular cavity from the smooth outflow portion—towards the pulmonary valve annulus and pulmonary trunk.

Its boundaries include:

• Inferiorly: The supraventricular crest, which marks the transition between the trabeculated right ventricle and the smooth RVOT.
• Medially: The infundibular septum, a muscular structure that separates the RVOT from the left ventricular outflow tract.
• Anteriorly and superiorly: The conus arteriosus, the funnel-shaped smooth chamber leading into the pulmonary valve.
• Laterally: The infundibular free wall, a smooth muscular wall continuous with the anterior wall of the right ventricle.
• Superiorly: The pulmonary valve and the pulmonary root, forming the continuity between the RVOT and the pulmonary arterial system.

Structural Components

Right Ventricular Infundibular Cavity

This cavity comprises the main lumen of the RVOT, characterized by smooth walls designed to facilitate laminar blood flow from the right ventricle to the pulmonary artery. The infundibular cavity narrows superiorly as it approaches the pulmonary valve, forming a funnel shape that enhances efficient ejection of blood.

Conus Arteriosus

The conus arteriosus refers to the conical outflow segment of the RVOT immediately proximal to the pulmonary valve. It is formed by the infundibular free wall and the infundibular septal boundary and serves as the transition zone between the ventricular cavity and the pulmonary valve orifice.

Smooth-Walled Outflow Region

Unlike the trabeculated inflow portion of the right ventricle, the RVOT is lined by smooth endocardium and myocardium, which reduces turbulence during systolic ejection. This region includes the infundibular free wall and the infundibular septal boundary.

Infundibular Free Wall

The infundibular free wall is the smooth muscular wall of the RVOT facing anteriorly and laterally. It is continuous with the anterior wall of the right ventricle and helps maintain the shape and integrity of the outflow tract.

Infundibular Septal Boundary

This muscular septum separates the RVOT from the left ventricular outflow tract (LVOT) and is critical in maintaining the anatomical and functional distinction between the right and left ventricular outflow pathways.

Functional Relationships

Supraventricular Crest and Outflow Tract

The supraventricular crest is a prominent muscular ridge that marks the boundary between the trabeculated inflow right ventricle and the smooth RVOT. It plays an important role in maintaining the separation of inflow and outflow blood streams and provides attachment for the septomarginal trabeculation and moderator band.

Trabeculated-Smooth Wall Transition

The transition from the trabeculated right ventricular body to the smooth RVOT is abrupt and marked by the supraventricular crest. This anatomical feature is essential for the functional compartmentalization of the right ventricle, optimizing both filling and ejection phases.

Outflow Tract Superior Narrowing

The RVOT narrows superiorly as it approaches the pulmonary valve, creating a conical shape that facilitates efficient blood flow and minimizes regurgitation. This narrowing is reinforced by the muscular infundibulum, which can contract to regulate outflow.

Outflow Tract-Pulmonary Root Continuity

At its superior end, the RVOT is continuous with the pulmonary root, which includes the pulmonary valve leaflets and the initial portion of the pulmonary artery. This continuity ensures unidirectional blood flow from the right ventricle to the lungs.

Right Ventricular Outflow Tract Map

The RVOT can be conceptualized as a three-dimensional map consisting of:

• The infundibular cavity, the lumen through which blood passes.
• The infundibular free wall, forming the anterior and lateral boundaries.
• The infundibular septal boundary, separating it from the left ventricle.
• The supraventricular crest, marking its inferior boundary.
• The pulmonary valve annulus and pulmonary root, marking its superior boundary.

This spatial organization is critical for understanding congenital and acquired pathologies affecting the right ventricular outflow tract, such as infundibular stenosis or arrhythmogenic right ventricular cardiomyopathy.

Where:

• r is the radius of the pulmonary valve annulus (base radius),
• h is the length of the infundibular cavity (height of the cone),

This formula approximates the volume of the RVOT given its conical geometry.

This detailed anatomical and functional description of the Right Ventricular Outflow Tract highlights its key components and relationships within the right heart, essential for understanding cardiac physiology and pathology.