4.5 Diaphragmatic Surface

Diaphragmatic Surface refers to the inferior surface of the heart that rests directly upon the diaphragm. This surface forms a broad, flattened region on the base of the heart, facing downward and slightly posteriorly, and is sometimes called the inferior surface. It is primarily formed by the left ventricle, with a lesser contribution from the right ventricle. The diaphragmatic surface is key in understanding cardiac orientation within the thoracic cavity and anatomical relationships with neighboring structures.

Extent and Boundaries

Surface Extent

The diaphragmatic surface extends from the acute (inferior) margin of the heart upward to the posterior aspect, forming a broad area that contacts the central tendon of the diaphragm. It is demarcated anteriorly by the inferior margin and posteriorly by the posterior interventricular groove. This surface is not truly flat; it is gently convex, matching the curvature of the diaphragm.

Chamber Contributions

The left ventricle forms the majority of this surface, while the right ventricle contributes near the inferior margin.

Anatomical Features

Posterior Interventricular Groove

The posterior interventricular groove (sulcus) is a key landmark on the diaphragmatic surface. It runs almost vertically and marks the boundary between the left and right ventricles on this surface. The posterior interventricular branch of the right coronary artery and the middle cardiac vein run within this groove.

Inferior Atrioventricular Groove

Also known as the coronary sulcus, this groove separates the atria from the ventricles along the diaphragmatic surface. It encircles the heart and is more pronounced posteriorly, housing the coronary sinus, which drains most of the cardiac venous blood.

Cardiac Crux

The cardiac crux is the intersection point of the posterior interventricular and atrioventricular grooves. It is an important landmark, as it is the site where the atrial and ventricular septa and the walls of all four chambers come together. The crux is also the location where the atrioventricular nodal artery commonly branches.

Morphological Map

This diagram shows the main features: the dominant left ventricular area (top), the right ventricular area (lower right), the posterior interventricular groove (vertical line), and the crux (yellow dot).

Inferior Vena Cava Entry and Related Structures

Inferior Vena Cava Entry

The inferior vena cava (IVC) pierces the diaphragm at T8 and enters the right atrium near the right margin of the diaphragmatic surface. Its point of entry can be palpated at the junction of the right atrium and the diaphragmatic surface, just to the right of the cardiac crux.

Relationships to Adjacent Structures

The diaphragmatic surface lies directly on the central tendon of the diaphragm. Inferiorly, it is related to the liver (mainly the left lobe) and, to a lesser extent, the stomach and esophagus posteriorly.

Functional and Clinical Significance

Cardiac Motion and Diaphragm

During the cardiac cycle, the diaphragmatic surface moves with the diaphragm during respiration. Its proximity to the diaphragm is relevant for the transmission of pericardial sounds and for certain imaging modalities (e.g., echocardiography via subcostal view).

Clinical Relevance

• Electrocardiography: Infarcts in the inferior wall of the heart are often due to occlusion of the right coronary artery, which supplies much of the diaphragmatic surface.
• Pericardial Effusion: Fluid accumulates first on the diaphragmatic surface due to gravity when a person is supine.
• Surgical Access: Subxiphoid pericardiocentesis targets the diaphragmatic surface to avoid puncturing the lungs.

Key Points Table

Summary

The diaphragmatic surface of the heart is its inferior aspect, primarily formed by the left ventricle, with a significant contribution from the right ventricle along the margin. This surface is marked by the posterior interventricular groove, the inferior atrioventricular groove, and the cardiac crux, which are critical for anatomical orientation and understanding cardiac circulation. Functionally, its relationship with the diaphragm and adjacent viscera is important in both health and disease, with particular clinical implications for imaging, diagnosis, and surgical intervention.