3 Pericardium and Cardiac Relations

Pericardium and Cardiac Relations refers to the anatomical configuration, structure, and spatial relationships of the pericardium—the double-walled sac surrounding the heart—and its association with the heart and adjacent thoracic structures. This includes the organization of the pericardium, its subdivisions, attachments, the pericardial cavity, and the way the pericardium interfaces with the heart, great vessels, and surrounding organs.

Pericardial Anatomy Scope

The pericardium consists of two main layers: the fibrous pericardium (a tough, external connective tissue layer) and the serous pericardium (a delicate, double-layered membrane). These components form a protective sac that encases the heart, providing mechanical protection, limiting excessive movement, and serving as a barrier against infection.

Fibrous Pericardium

The fibrous pericardium is a conical, inelastic structure composed of dense connective tissue. It is the outermost layer, enveloping the heart and the roots of the great vessels. This layer acts as a tough, protective envelope, preventing overdistension of the heart and anchoring it within the mediastinum.

• Attachments:
  • Superiorly, it is fused with the tunica adventitia of the great vessels (aorta, pulmonary trunk, superior vena cava).
  • Inferiorly, it is firmly attached to the central tendon of the diaphragm, providing stability during the cardiac cycle.
  • Anteriorly, it is loosely attached to the posterior surface of the sternum by sternopericardial ligaments.

Serous Pericardium

The serous pericardium is divided into two layers:

• Parietal Layer: Lines the internal surface of the fibrous pericardium.
• Visceral Layer (Epicardium): Closely adheres to the heart's surface and reflects onto the great vessels.

Between these layers lies the pericardial cavity, a potential space containing a thin film of serous fluid that reduces friction during cardiac movement.

Pericardial Cavity

The pericardial cavity is the potential space between the parietal and visceral layers of the serous pericardium. It normally contains 15–50 mL of pericardial fluid, which serves as a lubricant, allowing the heart to contract and relax with minimal friction.

Pericardial Sinuses and Recesses

During embryological development, the folding of the heart tube and the reflection of the serous pericardium around the great vessels create two important sinuses:

• Transverse Pericardial Sinus: A passageway posterior to the ascending aorta and pulmonary trunk, and anterior to the superior vena cava.
• Oblique Pericardial Sinus: A cul-de-sac located posterior to the left atrium, bounded by the reflections around the pulmonary veins and inferior vena cava.

Pericardial Attachments

The pericardium is anchored within the thorax by various attachments:

• Diaphragmatic Attachment: The fibrous pericardium fuses with the central tendon of the diaphragm, enabling synchronous movement during respiration and cardiac cycles.
• Sternal Attachment: Sternopericardial ligaments connect the fibrous pericardium to the posterior surface of the sternum, stabilizing the heart's anterior position.
• Vascular Attachments: The pericardium is continuous with the adventitia of the great vessels, providing further stability and anatomical continuity.

Anterior Cardiac and Pericardial Relations

Anteriorly, the pericardium and heart are related to the following structures:

• Sternum (Body and Xiphoid Process): The anterior aspect of the pericardial sac is separated from the sternum by loose connective tissue, fat, and, in children, the thymus gland.
• Costal Cartilages (2nd to 6th): These overlie the pericardium and heart, providing partial protection.
• Anterior Mediastinum: Contains connective tissue and lymphatics between the pericardium and sternum.

Posterior Cardiac and Pericardial Relations

Posteriorly, the heart and pericardium are related to:

• Esophagus: Lies directly posterior to the left atrium, separated by the pericardium.
• Descending Thoracic Aorta: Positioned to the left of the esophagus and pericardium.
• Thoracic Vertebrae (T5–T8): Provide a posterior boundary.
• Azygos and Hemiazygos Veins: Situated to the right and left, respectively.

Lateral Cardiac and Pericardial Relations

Laterally, the pericardium and heart are related to:

• Lungs and Pleura: The mediastinal pleura and lungs surround the pericardium on both sides, except in the area of the cardiac notch on the left, where the pericardium is in direct contact with the anterior thoracic wall.

Inferior and Superior Cardiac Relations

• Inferiorly: The pericardium rests on and is fused with the central tendon of the diaphragm. Below the diaphragm lies the liver, particularly the left lobe, separated by the diaphragm.
• Superiorly: The pericardium is continuous with the adventitia of the great vessels (ascending aorta, pulmonary trunk, superior vena cava, pulmonary veins). The superior limit of the pericardium lies at the level of the second costal cartilage.

Pericardial Neurovascular Anatomy

• Arterial Supply: The pericardium receives blood mainly from the pericardiacophrenic arteries (branches of the internal thoracic arteries), with contributions from the musculophrenic, bronchial, esophageal, and superior phrenic arteries.
• Venous Drainage: Pericardiacophrenic veins accompany the arteries and drain into the brachiocephalic or internal thoracic veins.
• Nerve Supply:
  • Phrenic Nerves (C3–C5): Provide sensory innervation to the fibrous and parietal serous pericardium.
  • Vagus Nerve: Contributes parasympathetic fibers.
  • Sympathetic Trunks: Contribute vasomotor fibers.

Pericardial Relationships to the Great Vessels

The pericardium is intimately related to the origins and initial segments of the great vessels:

• Ascending Aorta and Pulmonary Trunk: Both arise within the pericardial sac and are enveloped by the serous pericardium.
• Superior and Inferior Vena Cava: Surrounded at their cardiac entry points by the pericardium.
• Pulmonary Veins: Enter the left atrium within the pericardial cavity.

Integrated Pericardial and Cardiac Relations

The overall configuration of the pericardium ensures that the heart is protected, stabilized, and functions efficiently within the mediastinum. The pericardium’s close anatomical relationships with the diaphragm, sternum, lungs, and great vessels are vital for the physiological movement of the heart, the accommodation of changes in thoracic pressure, and the protection against infection or trauma.

The spatial arrangement can be summarized as follows:

• The pericardium forms a central compartment in the mediastinum, enclosing the heart and the origins of the great vessels.
• It acts as a mechanical barrier and provides a lubricated environment for cardiac motion.
• Its attachments maintain the heart’s position and limit excessive movement.

The pericardium’s neurovascular supply ensures adequate nutrition, drainage, and sensory feedback, which is especially important in disease states such as pericarditis or cardiac tamponade.

This integrated anatomical framework of the pericardium and its cardiac relations forms the basis for understanding both normal cardiac physiology and the clinical implications of pericardial diseases.