Pericardium: Layers and Structure

• Pericardium is a fibroserous membrane that covers the heart and the beginning of its great vessels.
• A closed sac forms the pericardium, and is composed of two layers.

Pericardium Layers

• Fibrous pericardium is a continuous, tough, external layer with the central tendon of the diaphragm.
• Parietal layer of serous membrane lines the internal surface of the fibrous pericardium.
• Serous pericardium is composed of mesothelium, a single layer of flattened cells forming epithelium.
• Mesothelium lines the internal surface of the fibrous pericardium and external surface of the heart
• Fibrous pericardium continues superiorly with the tunica adventitia of the great vessels.
• Great vessels enter/leave the heart, along with the pretracheal layer of deep cervical fascia.
• The sternopericardial ligaments attach the fibrous pericardium anteriorly, to the posterior surface of the sternum.
• Loose connective tissue binds the pericardium posteriorly to structures in the posterior mediastinum.
• Pericardiacophrenic ligament refers to the site of continuity where pericardium is continuous inferiorly with the central tendon of the diaphragm.
• The heart and roots of the great vessels in the pericardial sac are posterior to the sternum.
• The great vessel roots are behind costal cartilages, plus anterior ends of the 3rd-5th ribs on the left side.
• The heart and pericardial sac are situated obliquely with ~2/3 to the left and ~1/3 to the right of the median plane.
• The pericardial cavity, a potential space, lies between opposing parietal and visceral layer.
• The serous pericardium normally contains a thin film of fluid that allows the heart to move and beat without friction.
• The visceral layer of serous pericardium forms the epicardium, the outermost layer of the three heart wall layers.
• It extends onto the beginning of the great vessels.
• The Visceral layer becomes continuous with the parietal layer of serous pericardium where the aorta and pulmonary trunk leave the heart.
• The Visceral layer also becomes continuous where the SVC, inferior vena cava, and pulmonary veins enter the heart.

Sinuses of the Pericardium

• There are two sinuses in serous pericardium: transverse and oblique.
• Transverse sinus is in the recess behind the pulmonary trunk and ascending aorta.
• Anterior boundary: pulmonary trunk & ascending aorta
• Posterior boundary: SVC & upper part of the 2 atria
• Above boundary: rt. pulmonary artery.
• Below boundary: the 2 atria, mainly left.
• The transverse pericardial sinus is especially important to cardiac surgeons.
• A finger can be passed through the transverse pericardial sinus behind the aorta and pulmonary trunk once the pericardial sac is opened anteriorly.
• A surgical camp can pass by placing a ligature around the vessels, inserting tubes or performing cardiac surgery, such as a coronary artery bypass.
• The zone of reflection surrounding the veins is ‘J-shaped’.
• The cul-de-sac formed within the ‘J’, posterior to the left atrium, makes the oblique pericardial sinus.

Pericardium Arterial Supply

• The arterial supply comes mainly from a slender branch of the internal thoracic artery.
• The pericardiophrenic artery usually accompanies or parallels the phrenic nerve to the diaphragm.
• Smaller blood contributions come from:
• Musculophrenic artery, a terminal branch of the internal thoracic artery.
• Bronchial, esophageal, and superior phrenic arteries (branches of the thoracic aorta).
• Coronary arteries, the aorta's first branches that supply the visceral serous pericardium.
• Nerve supply to the pericardium comes from the phrenic nerves (C3-C5), the primary source of sensory fibers.
• Additional nerve supply comes from vagus nerves (function uncertain) and sympathetic trunks (vasomotor).