Heart Anatomy: Pericardium, Sinuses, Circulation & Tamponade

Location of the pericardial sac

Posterior to the body of the sternum and 2nd-6th costal cartilages, at the level of T5-T8

Pericardium: structure

Double-walled fibroserous membrane that encloses the heart and the roots of the great vessels

Fibrous pericardium: attachment

Blends with the central tendon of the diaphragm

Layers of the serous pericardium

Parietal layer (lines fibrous pericardium) and visceral layer (epicardium); the pericardial cavity between them holds a thin layer of fluid

Visceral layer of serous pericardium is also called the...

Epicardium

Pericardial attachments (position)

Fused with tunica adventitia of great vessels; posterior sternum via sternopericardial ligaments; central tendon of diaphragm

Functions of the pericardium

Protection from overfilling, stability (anchors heart), protection from infection

Transverse pericardial sinus

Passage posterior to the aorta and pulmonary trunk

Oblique pericardial sinus

Blind recess posterior to the heart

Main arterial supply to the pericardium

Pericardiacophrenic artery (branch of internal thoracic artery)

Smaller arterial branches supplying the pericardium

Musculophrenic artery (terminal branch of internal thoracic), bronchial, esophageal, and superior phrenic arteries

Arterial supply to the visceral layer of pericardium

Coronary arteries

Venous drainage of the pericardium

Pericardiacophrenic veins (tributaries of brachiocephalic) and tributaries of the azygos system

Sensory nerve supply of the pericardium

Phrenic nerves (C3-C5)

Pericardial pain is referred to...

Skin of the ipsilateral shoulder (via phrenic nerve)

Vagus nerve (CN X) and sympathetic trunks: role in pericardium

Vagus - nerve supply; sympathetic trunks - vasomotor

Heart: functional description

Double, self-adjusting muscular pump

Right side of the heart pumps...

Poorly oxygenated blood to the lungs

Left side of the heart pumps...

Well oxygenated blood from the lungs to the aorta

Epicardium

Thin external layer (mesothelium); formed by the visceral layer of serous pericardium

Myocardium

Thick middle layer of cardiac muscle

Endocardium

Thin internal layer (endothelium and subendothelial connective tissue); also covers the valves

Position of the heart in the chest

Anterior to sternum, costal cartilages and medial ends of left 3rd-5th ribs; lies obliquely, ~2/3 left and 1/3 right of the median plane

Shape of the heart

Tipped-over, three-sided pyramid with an apex, a base and four surfaces

Location of the apex of the heart

Posterior to the left intercostal space, ~9 mm from the median plane; mitral valve is best heard here

Base of the heart

Posterior aspect; formed mainly by the left atrium, with some right atrium

Four surfaces of the heart

Anterior, diaphragmatic (inferior), left pulmonary, right pulmonary

Four borders of the heart

Right, inferior, left, superior

Right atrium: what enters it

Venous blood from the SVC, IVC and coronary sinus

Right auricle

Ear-like conical muscular pouch that increases the capacity of the right atrium

Coronary sinus: location

Posterior part of the coronary sulcus; receives blood from the coronary veins

Sinus venarum

Smooth-walled posterior part of the RA where the SVC, IVC and coronary sinus open

Sulcus terminalis vs. crista terminalis

Sulcus terminalis = external terminal groove; crista terminalis = internal terminal crest

Pectinate muscles

Rough, muscular ridges of the atrial wall (RA, and in the left auricle)

Interatrial septum

Separates the right and left atria

Oval fossa

Thumbprint-sized depression in the interatrial septum; remnant of the oval foramen and fetal valve

PFO (patent foramen ovale)

Failure of the fetal oval foramen to close, leaving a communication between RA and LA

Right AV orifice

Tricuspid orifice - opening from RA into RV

Trabeculae carneae

Irregular muscular elevations on the inner ventricular walls

Supraventricular crest

Thick muscular ridge separating the muscular inflow part of the RV from the smooth-walled outflow part

Interventricular septum: parts

Membranous and muscular; partition between the RV and LV

Septomarginal trabecula (moderator band)

Muscular bundle from the inferior IV septum to the anterior papillary muscle; carries the right bundle branch

VSD (ventricular septal defect)

Defect in the interventricular septum (membranous or muscular) allowing communication between RV and LV

Left atrium: key features

Forms most of the base of the heart; large, smooth-walled, thicker than RA

Pulmonary veins entering the LA

Pairs of valveless right and left pulmonary veins enter the posterior wall

Left auricle

Forms the superior part of the left border; lined with pectinate muscle

Left ventricle: workload and wall thickness

Performs the most work; walls 2-3 times thicker than the RV because systemic arterial pressure is much higher

Aortic vestibule

Smooth-walled, nonmuscular outflow tract of the left ventricle

Tricuspid valve: location and cusps

Guards the right AV orifice; anterior, posterior and septal cusps

Chordae tendineae: function

Attach to free edges and ventricular surfaces of cusps; attach to adjacent cusps to prevent prolapse

Papillary muscles

Bases attach to ventricular wall, apices to chordae tendineae; begin to contract before ventricular contraction to tighten the cords

Pulmonary valve: location

Apex of the conus arteriosus, at the level of the left 3rd costal cartilage

Pulmonary valve cusps

Semilunar cusps: anterior, right and left

Mitral valve: cusps

Double leaflet: anterior and posterior (left AV orifice)

Mitral valve: surface location

Posterior to the sternum at the level of the 4th costal cartilage

Mitral valve: how backflow into LA is prevented

Chordae tendineae become taut just before and during systole

Aortic valve: surface location

Posterior to the left side of the sternum at the level of the 3rd intercostal space

Aortic valve cusps

Right, left and posterior ("non-coronary")

Aortic sinuses

Spaces at the origin of the ascending aorta between the aortic wall and the valve cusps

Why do the coronary arteries fill in diastole?

Recoil of the elastic aorta causes backflow of blood that closes the aortic valve and fills the coronary arteries

Lymphatic drainage of the heart

Myocardial/subendocardial lymphatics → subepicardial plexus → coronary sulcus, following coronary arteries → inferior tracheobronchial lymph nodes (right side)

Right coronary artery (RCA): origin

Right aortic sinus of the ascending aorta

Left coronary artery (LCA): origin

Left aortic sinus of the ascending aorta

Main branches of the LCA

Anterior interventricular (LAD) and circumflex arteries

Typical territory of the LAD

Anterior wall of LV, anterior two-thirds of IV septum, apex

Typical RCA branches

SA nodal artery, right marginal artery, posterior interventricular (PDA, in right-dominant hearts), AV nodal artery

Great cardiac vein

Accompanies the LAD (anterior interventricular vein) and drains to the coronary sinus

Conduction pathway of the heart

SA node → AV node → bundle of His → right/left bundle branches → Purkinje fibers

Cardiac tamponade

Accumulation of fluid/blood in the pericardial cavity compressing the heart and limiting filling

Atrial fibrillation

Chaotic, disorganized atrial electrical activity producing an irregularly irregular rhythm