01 Cardiac Anatomy

External Anatomy

Pericardium

_The pericardium is double-walled sac that encloses the heart and great vessel roots..

_Pericardium composed of 2 layers:

Fibrous pericardium on outside
Serous pericardium on inside, made up of parietal and visceral layers..

Fibrous Pericardium

_Strong external layer that limits the expansion of the pericardial cavity; it is continuous with the adventitia that surrounds the great vessels entering and exiting the heart.,

_Fused to the diaphragm on its inferior surface and is anchored to the sternum by connective tissue called the sternopericardial ligaments.,

Serous Pericardium

_Composed of parietal and visceral layers:

Parietal layer: The parietal layer forms the inner layer of the fibrous pericardium and is the most external layer of the serous pericardum; it is fused to the fibrous pericardium, which is external to the parietal layer.
Visceral layer (epicardium): The visceral layer covers the external surface of the heart itself and is the innermost layer of the pericardium deep to the parietal layer and fibrous pericardium..

_Pericardial fluid collect between visceral and parietal layer of serous pericardium, the pericardial cavity..

Transverse pericardial sinus

_An anatomical space within the pericardial cavity posterior to the pulmonary trunk and ascending aorta but anterior to the superior vena cava.,

Oblique pericardial sinus

_Space on the posterior aspect of the left atrium; it is formed by reflections of pericardium from where the IVC, SVC, and pulmonary veins enter into the heart. The right border is formed by the IVC and right pulmonary veins and the left border is formed by the left pulmonary veins.,

Posterior heart surface

_Defined by left atrium and a portion of the right atrium.,

_Esophagus sits between LA and aorta..

Diaphragmatic surface

_Aka inferior surface of heart.,

_Comprised by 2/3 of the left ventricle and 1/3 of the right ventricle.,

Coronary Sulcus

_Separates the ventricles and atria are circumferentially.,

_The structure is also known as the coronary or atrioventricular groove.,

Sternocostal surface

_Aka anterior surface of heart.,

_Is comprised of 2/3 right heart and 1/3 left heart — centrally by the RV and by the RA and LV on their corresponding sides.,

Heart Apex

_Approximately 8 cm left of the median plane in the 5th intercostal space; formed by the left ventricle.,

Heart Base

_A region where the aorta, pulmonary trunk, and SVC emerge from the heart. Found immediately deep to the sternal angle and the left and right portions of the 2nd intercostal spaces.., Left atrium is considered the base of the heart.

Heart Right Border

_Formed by the right atrium.,

Heart Left Border

_Formed by the left ventricle.,

Heart Inferior Border

_Formed by the right ventricle and a small portion of the left ventricle near the apex of the heart.,

Internal Anatomy

_Cardiac Myocytes form the myocardium on a microscopic level. They are precisely coordinated by gap junctions within intercalated discs that allow rapid spread of electrical signals between cells..

SA Node

_The pacemaker of the heart. Exhibits automaticity by spontaneously generating action potentials. Located at the junction of the superior vena cava and the right atrium. Initiates the electrical impulses to stimulate contraction.,

AV node

_Located between the atria and ventricles and conducts the signal from the sinoatrial node to the rest of the heart. It slows down conduction between the atrium and the ventricles, allowing time for the ventricles to fill with blood before contraction.,

Bundle of His

_Bundle of specialized cardiomyocytes (bigger cells with fewer contractile elements → less electrical resistance) that propagate signals from the AV node down into the ventricles., Clinical Correlate: Defects in the His-Purkinje system are responsible for second degree heart block: Mobitz type 2.

Left and Right Bundle Branches

_Branches of the bundle of His that conduct to the left and right ventricles via Purkinje fibers. Clinical Correlate: These can become blocked in heart failure → left or right bundle branch block..

Purkinje fibers

_Located along the edges of each ventricle, conduct the signal from the bundle of His and bundle branches to ventricular cardiomyocytes.,

Right Atrium

_Receives deoxygenated blood from the inferior vena cava, superior vena cava, and coronary veins.,

Sinus Venarum

_Smooth internal portion of the posterior right atrium in between the two vena cavae and includes the interatrial septum. It is the incorporated adult remnant of the embryonic sinus venosus.,

Crista Terminalis

_Internal muscular ridge that divides the right atrium into the atrium proper and the vena caval area.,

Atrium Proper

_Trabeculated part of the right atrium lined with pectinate muscles, which are bundle muscle fibers found predominately within the auricle, an ear-shaped appendage. Note: Pectinate muscles are also present in the left atrium but are less prominent.,

Fossa Ovalis

_Depression in the interatrial septum and the remnant of the foramen ovale; lateral and superior borders form the limbus of the fossa ovalis.,

Right Ventricle

Trabeculate carneae

_Thick bundles of muscle that give the right ventricle its rough texture; thicker than the pectinate muscles of the atria.,

Papillary Muscles

_Projections of ventricular muscle that are attached to the cusps of atrioventricular valves via the chordae tendineae preventing valvular prolapse during systole. Note: Please see associated image for the relationship of the three structures.,

Septomarginal trabeculae

_Aka moderator band.,

_Connecting bridge between the interventricular septum and the root of the anterior papillary muscle.,

Chordae Tendinae

_Fibrous cords that attach the papillary muscles to the valve cusps; the tension created by contracting papillary muscles and taut chordae tendinae prevent the cusps of the AV valve from prolapsing into the atrium as the ventricle contracts and the pressure on the valve increases.,

Left Atrium

[_](Left atrium location and why it's important)The most posterior chamber of the heart. Anterior to the esophagus. Thus, enlargement can cause:

Dysphagia by compressing the esophagus
Hoarseness by compressing the left recurrent laryngeal nerve.,

Esophagus: black hole between aorta and left atrium

Left Ventricle

_The wall of the left ventricle is approximately 3x as thick as that of the right ventricle under non-pathological conditions..

Aortic Vestibule

_Aka outflow tract of left ventricle.,

_The smooth portion of the left ventricle immediately proximal to the aortic valve.,

Valves

_The anterior cusp of the mitral valve separates the outflow tract from the inflow tract (trabeculated tract)..

Aortic orifice

_Includes the aortic valve and lies posteriorly and to the right of the pulmonary orifice..

Left atrioventricular orifice

_Defined by the bicuspid (mitral) valve; located posteriorly and to the left of the aortic orifice and to the left of the right atrioventricular orifice..

Mitral and Tricuspid Valves

_Left atrioventricular (bicuspid/mitral) valve: The mitral valve is composed of anterior and posterior cusps; the anterior and posterior papillary muscles attach to the cusps via chordae tendinae

Right atrioventricular (tricuspid) valve: The right atrioventricular valve is formed by the anterior, posterior, and septal cusps..

Anuli fibrosis

_Fibrous rings of connective tissue that encompass each of the 4 valvular orifices; provide stable attachment sites and support for the cusps of the valves.,

Fibrous trigones

_Triangular-shaped fibrous connective tissue structures. The left side is between the annuli fibrosis of the aortic and mitral orifices; the right side is situated between the annuli fibrosis of the tricuspid, mitral, and aortic orifices. Function: Provide structural support for the valves of the heart and are components of the fibrous skeleton of the heart.,

Cardiac Blood Supply

_There are two main coronary arteries, the left coronary artery (LCA) and right coronary artery (RCA)..

LCA

_Originates from the left aortic sinus and bifurcates into:

LAD (left anterior descending) artery, which gives off superficial (diagonal) and multiple deep (septal perforator) branches. anterior LV
LCX (left circumflex) artery ..

_Supplied by the ascending aorta.,

LCX

_Wraps around the left border of the heart within the coronary sulcus.,

_Supplies:

Posterolateral wall of left ventricle
Anterolateral papillary muscle along with LAD.,

LAD

_Aka anterior interventricular artery.,

_Passes within the anterior interventricular sulcus toward the apex.,

_Supplies:

Anterior wall of left ventricle
Anterior 2/3 of the interventricular septum, or superior septum
Anterolateral papillary muscle along with LCX.,

_Since the anterolateral papillary muscle is supplied by both the LAD and LCX, it is relatively resistant to infarction. In contrast, the posteromedial papillary muscle is more susceptible to ischemic injury since it is supplied by a single arterial branch: the PDA depending on dominance of the heart..

RCA

_Originates from right aortic sinus and upplies:

Right atrium and ventricle (inferior walls) via right marginal artery
Left ventricle (diaphragmatic surface) via right marginal artery
Posterior 1/3 of the interventricular septum or the inferior septum via PDA
Right posteromedial papillary muscle via PDA
AV node (in right-dominant individuals) via AV nodal artery from PDA
SA node via SA nodal artery..

_The RCA travels in the coronary sulcus between RA and RV and passes around right border of heart between the posterior and diaphragmatic surfaces..

_Gives rise to the 4 branches below:

Right marginal branch
SA nodal artery
PDA that also gives rises to AV nodal artery.,

Right marginal branch

_Arises from the RCA before it crosses the right border of the heart and travels along the acute margin just superior to the inferior border (see image); supplies the right ventricle.,

SA nodal artery

_Has a variable course of travel and can encircle the SVC either posteriorly or anteriorly; during posterior circling, the artery travels left of the SVC, circles around the posterior aspect of the vessel, and emerges anteriorly on the right side of the SVC to supply the SA node.,

AV nodal artery

_Supplies the AV node (90% of patients AV nodal artery, 10% LCX). Comes off off PDA.,

PDA

_Aka posterior interventricular artery (PIV).,

_Emerges from the RCA after leaving the coronary sulcus and descends toward the apex of the heart (70% of population).,

_Supplies:

Posterior 1/3 of interventricular septum or inferior septum
Posterior walls of ventricles
Posteromedial papillary muscle.,

_The artery that supplies the PDA is the structure that determines coronary dominance:

Right dominant — PDA is supplied by the RCA (85% of population)
Left dominant — PDA is supplied by the LCX (8% of population)
Co-dominant — PDA is supplied by both the RCA and LCX (7% of population)..

Heart Veins

_Primarily drain to the coronary sinus, which empties directly into the right atrium..

Great cardiac vein

_Originates in the anterior interventricular sulcus; travels first with the left anterior descending artery (LAD) and then alongside the left circumflex artery (LCX).,

Middle cardiac vein

_Ascends in the posterior interventricular sulcus with the posterior interventricular artery.,

Small cardiac vein

_Runs alongside the right marginal artery before traveling posteriorly in the right coronary sulcus with the right coronary artery; drains into the coronary sinus near its junction with the right atrium.,

Anterior cardiac veins

_Originate on the anterior wall of the right ventricle, cross the coronary sulcus, and drain into the right atrium.,

Smallest (thebesian) veins

_Are found in the walls of myocardium of the 4 chambers of the heart; drain directly into the chambers.,

_aka venae cordis minimae.,

_Branches of aorta, ABC’S:

Aorta
Brachiocephalic trunk — Gives rise to the right common carotid and right subclavian
Common carotid (left)
Subclavian artery (left)..

Brachiocephalic Artery

_The first branch of the aortic arch, which immediately branches into the right common carotid and right subclavian arteries to supply the right arm, neck and head.,

Left common carotid artery

_The second branch of aortic arch, which supplies the left side of the neck and head.,

Left subclavian artery

_The third branch of aortich arch, which primarily supplies the left arm.,

Both the right and left subclavian arteries give off multiple branches that enter and supply the neck region.

Pulmonary arteries

_Branches of the pulmonary trunk and carry deoxygenated blood to the lungs..

Right pulmonary artery

_Longer than the left and enters the hilum of the right lung between the right pulmonary vein and intermediate bronchus..

Left pulmonary artery

_Shorter, enters the hilum of the left lung posterior to the left pulmonary vein and superior to the left primary bronchus..

Ligamentum arteriosum

_A fibrous remnant of the ductus arteriosus attaching the left pulmonary artery to the aortic arch.,

_The relationship of the pulmonary artery to the bronchus can be remembered with the mnemonic: RALS..

Right — Anterior (right pulmonary artery is anterior to right intermediate bronchus)
Left — Superior (left pulmonary artery is superior to the left principal bronchus)..