4.4 Sternocostal Surface
The sternocostal surface is the anterior chest wall formed by the sternum and ribcage, providing structural support and housing vital thoracic organs.
Sternocostal Surface refers to the anterior (front) aspect of the heart that faces towards the sternum and adjacent costal cartilages. It is also known as the anterior surface of the heart and is a key anatomical area for clinical examination, imaging, and surgical approaches.
Extent and General Features
The sternocostal surface is primarily oriented anteriorly and slightly to the left, lying immediately behind the sternum and the ribs. This surface is mostly covered by the pericardium, but its underlying structures are critical to understanding cardiac anatomy and pathology.
This surface is not flat; it is gently convex and is formed by contributions from multiple heart chambers. Its boundaries are defined superiorly by the origins of the great vessels (ascending aorta and pulmonary trunk) and inferiorly by the acute margin, which is the sharp lower border of the right ventricle.
Chamber Contributions
Right Ventricle
The right ventricle makes up the largest portion of the sternocostal surface. It occupies the inferior two-thirds of this area, forming the majority of what is visible from the anterior view. The acute or inferior margin of the heart, a sharp edge seen on this surface, is created by the right ventricle.
Right Atrium
The right atrium contributes to the upper right portion of the sternocostal surface. Its auricle, a small muscular pouch, is also visible extending from the chamber on this aspect.
Left Ventricle
The left ventricle contributes a smaller area to the left side of the sternocostal surface. It is separated from the right ventricle by the anterior interventricular groove and forms a rounded edge on the left margin.
Left Auricle
The left auricle, a finger-like projection from the left atrium, appears on the upper left part of the sternocostal surface. It partly overlaps the pulmonary trunk at its emergence.
Grooves and Landmarks
Anterior Interventricular Groove
Running down the sternocostal surface is the anterior interventricular groove, marking the boundary between the right and left ventricles. This groove contains the anterior interventricular branch of the left coronary artery (left anterior descending artery) and the great cardiac vein.
Atrioventricular Groove
The coronary (atrioventricular) groove marks the separation between the atria and ventricles. On the sternocostal surface, it is most prominent on the right side where the right coronary artery passes.
Great Vessel Emergence
Pulmonary Trunk
The pulmonary trunk emerges from the superior part of the right ventricle and ascends slightly leftward and posteriorly. Its origin is visible on the sternocostal surface, anterior and to the left of the aorta.
Ascending Aorta
The ascending aorta arises from the left ventricle, posterior to the pulmonary trunk, and is visible at the superior margin of the sternocostal surface. The aorta and pulmonary trunk together form the base for the attachment of the pericardium.
Sternocostal Surface Chamber Map
The distribution of the heart chambers on the sternocostal surface can be summarized as follows:
| Chamber | Relative Position | Percentage of Surface |
|---|---|---|
| Right Ventricle | Central, inferior | ~2/3 |
| Right Atrium | Right, superior | ~1/6 |
| Left Ventricle | Left, lateral | ~1/6 |
| Left Auricle | Superior, left (small) | Minimal |
Diagram: Sternocostal Surface of the Heart
Clinical and Functional Relevance
The sternocostal surface is of great clinical importance. Palpation and auscultation of the heart, as well as certain imaging techniques like echocardiography and chest X-rays, focus on this surface. It is the access route for pericardiocentesis and is exposed during open-heart surgery via median sternotomy.
Conditions such as anterior myocardial infarction commonly affect the right or left ventricles as visualized on the sternocostal surface. The distribution of coronary arteries and veins on this surface is crucial in diagnosing and managing ischemic heart disease.
Summary Table: Sternocostal Surface Structures
| Structure | Location/Relation | Notes |
|---|---|---|
| Right Ventricle | Central, most anterior | Forms acute margin; most of surface |
| Left Ventricle | Left, lateral | Forms obtuse margin |
| Right Atrium | Right, superior | Contains right auricle |
| Left Auricle | Left, superior | Overlaps pulmonary trunk |
| Anterior Interventricular Groove | Between ventricles | Contains LAD artery, great cardiac vein |
| Atrioventricular Groove | Atria/ventricles boundary | Contains right coronary artery |
| Pulmonary Trunk | Superior, left of aorta | Emerges from right ventricle |
| Ascending Aorta | Superior, right of pulmonary | Emerges from left ventricle |
Key Points
- The sternocostal surface is the anterior aspect of the heart, facing the sternum and ribs.
- It is formed mainly by the right ventricle, with contributions from the right atrium, left ventricle, and left auricle.
- Major grooves and landmarks (anterior interventricular and atrioventricular) and the origins of the great vessels are visible on this surface.
- Understanding the sternocostal surface is essential for clinical examination, cardiac imaging, and surgical procedures.