3. Pericardium & Heart

Venae Cordis Minimae

(least cardiac veins or Thebesian veins) - Very (VERY!!) small vessels that begin in the myocardium - Open directly into all four chambers of the heart but mainly into the atria - ESPECIALLY LEFT ATRIUM (Galen)

Trace the course of sensory fibers from the heart to the central nervous system. Locate the cell bodies of pain fibers supplying the heart.

- Afferent fibers from the heart primarily mediate sensations of pain. - These fibers course to the CNS with the branches of the sympathetic trunk to the heart, involving cardiac (visceral) branches from upper thoracic sympathetic ganglia and white rami of the upper four thoracic nerves. - The cell bodies of the pain fibers are in the first four thoracic DRG

Do anastomoses normally exist between coronary arteries or their major branches?

- Although the branches of the coronary arteries are considered to be functionally end arteries, there are anastomoses which may become enlarged and have the potential for collateral circulation. - These anastomoses generally occur at locations where branches of left and right coronary arterial branches are in close proximity (apex, etc.)

Anatomy of the Heart on the Thoracic Surface

- Apex - Left border (obtuse margin) - Superior border - Right border - Inferior border (acute margin)

Mitral valve

- Bicuspid valve - best heard in the 5th intercostal space just medial to the midclavicular line. - The apex beat or PMI (point of maximum impulse) occurs here.

What nerves supply the heart? Contrast the effects of sympathetic and parasympathetic stimulation of the heart.

- Cardiac branches of the vagus and the sympathetic trunk - Activation of sympathetic fibers increases the rate and strength of myocardial contraction - Parasympathetic stimulation results in a decrease in heart rate and little if any effect on force of contraction.

Conducting System

- Composed of specialized cardiac muscle fibers (not nervous tissue). - Sinoatrial (SA) node - Atrioventricular (AV) node - Atrioventricular (AV) Bundle of His - Purkinje fibers

Left Atrium

- Forms most of the anatomical base of the heart and lies directly posterior to the right atrium. It is the most posterior chamber of the heart. - Its interior is smooth except for a few musculi pectinati in the left auricle. It receives the four pulmonary veins (two left, two right).

Left Ventricle

- Forms the apex of the heart and most of its left border and diaphragmatic surface. - Its wall is approximately three times as thick as that of the right ventricle and its internal surface is lined with many trabeculae carneae. - Has two papillary muscles, an anterior and a posterior attached to the cusps of the bicuspid valve by chordae tendineae. - Bicuspid (mitral) valve: Has anterior and posterior cusps. - Aortic semilunar valve: Has three cusps, right, left, and posterior. Above the three cusps are dilations called the aortic sinuses (of Valsalva). - The right and left coronary arteries take origin from the right and left aortic sinuses, respectively.

Right Ventricle

- Forms the inferior border of the heart. - It is also the most anterior chamber of the heart. - The conus arteriosus is the funnel-shaped, smooth-walled, superior part of the right ventricle that gives origin to the pulmonary trunk. (Because of its funnel shape, it is also called the infundibulum. It lies directly anterior to the root of the aorta.) - A prominent ridge of myocardium, the supraventricular crest, separates the conus from the rest of the right ventricle, which has a trabeculated appearance from the many ridges of myocardium, or trabeculae carneae, that line its walls. - The septomarginal trabecula (moderator band) is a bridge of myocardium that crosses from the septum to the base of the anterior papillary muscle and carries part of the right crus of the atrioventricular bundle. - There are usually two other papillary muscles, the posterior and septal which, like the anterior, are attached to cusps of the tricuspid valve by chordae tendineae. - Tricuspid valve: cusps are anterior, septal, and posterior. - Pulmonary semilunar valve: Located at the superior end of the conus arteriosus. Has three cusps, anterior, right, and left.

Right Atrium

- Forms the right border of the heart. - Develops from the *right half of the sinus venosus* and the *right half of the primitive atrium* - The part from the *sinus venosus* is smooth walled and receives the openings of the *coronary sinus* and the *superior and inferior venae cavae*. - The part from the *primitive atrium* is rough-walled with ridges called *musculi pectinati* and includes the *right auricle*. - The *sulcus terminalis* is the external landmark separating the sinus venosus from the primitive atrium. (The internally the *crista terminalis* is the line of separation.) - The *fossa ovalis* on the interatrial septum is a remnant of the fetal foramen ovale. - The floor of the fossa ovalis is derived from the *septum primum*. - The *limbus fossae ovalis* is a muscular ridge around the fossa ovalis derived from the margin of the *septum secundum*.

Tributaries of the coronary sinus:

- Great cardiac vein - Middle cardiac vein - Small cardiac vein - Oblique vein of the left atrium

Interventricular Septum

- Has a large muscular part and a thin, oval membranous part. - The membranous part is the usual site of ventricular septal defects which are the most common of all congenital cardiac defects.

Left Dominance

- In ~10% of hearts, only the circumflex artery reaches the posterior interventricular sulcus and gives off the posterior interventricular artery and, thus supplies the posterior part of the septum and part of the right ventricle. - Since the anterior part of the septum is almost always supplied by a branch of the left coronary artery, occlusion of the main trunk of the left coronary in this type of heart can have disastrous results. - Entire blood supply to interventricular septum is by left coronary artery

Balanced Dominance

- In ~20 % of hearts both the right coronary and circumflex arteries reach the posterior interventricular sulcus. - Even though the posterior interventricular artery is still usually a branch of the right coronary, the posterior septum may be supplied by a number of small branches from either the left coronary, the right coronary, or both.

Right Dominance

- In ~70% of hearts the right coronary passes to the posterior interventricular sulcus and supplies part of the left ventricle and the posterior part of the interventricular septum. - In right dominant heart, blood supply to the interventricular septum is shared - 1/3 of supply to posterior interventricular artery - 2/3 anterior interventricular artery

Cardiac plexus

- Made up of a number of visceral branches from the cervical and thoracic sympathetic trunks and from both vagus nerves. - *Postganglionic sympathetic* fibers from *all the cervical sympathetic ganglia* and from the *first four thoracic sympathetic ganglia* enter the cardiac plexus. Sympathetic stimulation increases the heart rate and the force of contraction. - *Preganglionic vagal* fibers also enter this plexus. Vagal (parasympathetic) stimulation slows the heart rate and reduces the force of contraction - Pain fibers from nerve cells in the *first four thoracic dorsal root ganglia* are distributed to the heart through the visceral branches from the thoracic sympathetic ganglia. These fibers are stimulated by ischemia (lack of blood) which results in pain that is referred to the left side of the chest and the medial surface of the left arm.

What types of fibers, functionally and structurally, are found in the cardiac plexus?

- The cardiac plexus contains 3 types of fibers: afferent, preganglionic efferent (parasympathetic), and postganglionic efferent (sympathetic). - Parasympathetic fibers are supplied by the vagus - Sympathetic from the cervical and thoracic sympathetic ganglia - Afferent fibers from both vagus and sympathetic trunk. - Afferent for pain pain from the heart travel with the sympathetic system (processes of nerve cells located in the first four thoracic DRG) - Afferent for cardiorespiratory reflex fibers reach CNS via the vagus

Outline the projection of the heart on the anterior thoracic wall.

- The right border of the heart extends from the 3rd costal cartilage about a finger's breadth to the right of the sternum to the 6th costal cartilage at the sternocostal junction. - The apex lies in the 5th intercostal space in the midclavicular line. - The left border of the heart extends from the apex in a curving line to the 2nd intercostal space at the sternocostal junction.

Great cardiac vein

- Tributary of the coronary sinus - Begins at apex of the heart and accompanies the anterior interventricular artery to the coronary sulcus where it runs with the circumflex artery. - Becomes the coronary sinus at the point where the oblique vein of the left atrium unites with it. - Drains that part of the heart supplied by both branches of the left coronary artery.

Middle cardiac vein

- Tributary of the coronary sinus - Begins at the apex of the heart and accompanies the posterior interventricular artery to the coronary sulcus where it drains into the coronary sinus almost at the point where the coronary sinus terminates in the right atrium.

Small cardiac vein

- Tributary of the coronary sinus - Begins near the acute margin and accompanies the right coronary artery in the posterior part of the atrioventricular sulcus. - Drains into the coronary sinus at or near the point of termination of the middle cardiac vein. - Together, the middle and small cardiac veins drain blood from the part of the heart supplied by the right coronary artery.

Oblique vein of the left atrium

- Tributary of the coronary sinus - The adult derivative of the left common cardinal vein.

Anterior Cardiac Veins

- Two to four small veins that drain directly into the *right atrium*. - They begin on the anterior surface of the right ventricle and cross superficial to the right coronary artery.

Right Border

- a line from the right 3rd costal cartilage to the right 6th costal cartilage. - Formed by the superior vena cava, the right atrium, and the inferior vena cava.

What structures are innervated by the phrenic nerve?

- diaphragm - portions of the parietal pleura (mediastinal) - portions of pericardium adjacent to the nerve.

Left Border

- from the apex to the left 2nd costal cartilage. - Formed mostly by the obtuse margin of the left ventricle

Apex

- in the left 5th intercostal space, just medial to the midclavicular line. - Formed by the tip of the left ventricle

Pericarditis

1. Acute inflammation of the serous pericardial sac, often brought about by rheumatic fever or other bacterial, viral or tuberculosis infections as well as metabolic disorders such as uremia. 2. Causes diffuse substernal pain and pericardial effusion (leakage of fluids from the capillaries into the pericardial cavity). 3. Pericardial effusion may compress the pulmonary veins as they pass across the pericardial sac due to the inelasticity of the fibrous pericardium, causing alterations in the action of the heart known as *cardiac tamponade* 4. *Pericardiocentesis* is the draining of this excess fluid by the placing of a needle at the left infrasternal notch into the pericardial sac

Blood Supply of the Pericardium

1. Anterior and lateral surfaces of parietal pericardium: internal thoracic arteries via pericardiacophrenic and musculophrenic branches 2. Posterior surface of parietal pericardium: aorta via bronchial, esophageal, superior phrenic branches, and pericardial 3. Visceral pericardium: coronary arteries Note: Parietal pericardium supply is body wall derived.

Left coronary artery

1. Arises from the left aortic sinus 2. Passes between the left auricle and the pulmonary trunk to end in the following terminal arteries: 3. *Anterior interventricular artery* (Anterior descending or left anterior descending [LAD]) A branch of the left coronary artery Supplies both ventricles and interventricular septum One of the septal branches supplies the AV bundle (of His) and the bundle branches of the conducting system 4. *Circumflex artery* A branch of the left coronary artery Follows the coronary sulcus around the left side of the heart to posterior surface Supplies both left ventricle and left atrium

Right coronary artery

1. Arises from the right aortic sinus 2. Runs in atrioventricular (coronary) sulcus around the right side of the heart, past the posterior interventricular sulcus, to supply posterior surface of the left ventricle 3. Branches: -Artery to sinoatrial (SA) node -Right Marginal Artery (supplies right ventricle only) -Artery to atrioventricular (AV) node -Posterior Interventricular (Posterior descending) Artery

Coronary sinus

1. The main vein of the heart. 2. Opens into right atrium and drains all the venous blood from the heart, *except that returning through the anterior cardiac veins and the venae cordis minimae* 3. Begins at the point where the oblique vein of the left atrium joins the great cardiac vein. 4. Derived from the left horn of the sinus venosus.

Innervation of Pericardium

1. Visceral pericardium—innervated like the underlying heart 2. Parietal pericardium: Somatic afferents-- (1) phrenic nerves: lateral, posterior, inferior; pain of pericarditis felt on body wall (2) intercostal nerves: anterior

Moderator band

A prominent band of muscle fibers at the apex of the right ventricle which usually carries a branch of the atrioventricular bundle of conduction fibers to the septum; also called the septomarginal trabecula.

Atrioventricular node

A second mass of modified cardiac muscle fibers located in the interatrial septum just above the opening of the coronary sinus. (b)

Pericardium

A. Fibrous Pericardium (a) 1. Derived from the pleuropericardial membrane. 2. Fused with the central tendon of the diaphragm and will move with respiration. B. Serous Pericardium 1. Parietal layer (b) - lines inner surface of fibrous pericardium; derived from somatic mesoderm. 2. Visceral layer (d) - covers surface of the heart; derived from splanchnic mesoderm. 3. Pericardial cavity (c) - normally contains only a thin film of fluid, but can expand to hold about 300 ml

Surface Anatomy of The Heart Valves

Although the heart valves are located posterior to the sternum, the sounds made by these valves are best heard where they are carried in the direction of blood flow downstream of the valve. - Aortic valve - Pulmonary valve - Tricuspid valve - Mitral valve

What are the boundaries of the anterior mediastinum?

Anterior - central portions of body of sternum and transversus thoracis muscle. Posterior - central part of anterior wall of pericardial sac. Lateral - anterior part of mediastinal pleura. Inferior - anterior part of diaphragm. Superior - anterior part of imaginary line from sternal angle to intervertebral disc between T4 & T5.

Atrioventricular Bundle of His

Arises in the A-V node (c) and passes adjacent to the membranous part of the interventricular septum. Divides into right and left bundle branches that pass on either side of the muscular part of the interventricular septum (d). A portion of the right bundle branch passes to the anterior papillary muscle of the right ventricle through the septomarginal trabecula, i.e., moderator band (f)

Trabeculae carneae

Bands of muscle fibers on the inner surface of the ventricles.

Oblique sinus

Blind segment of pericardial sac bounded by the reflection of the serous parietal to the visceral pericardium around the pulmonary veins and the venae cavae.

Trace the stimulating impulse of the heart from the pacemaker to the apex of the left ventricle, naming all the components of the conduction system involved.

Conduction Pathway: sinoatrial node; muscle of atrium; atrioventricular node; atrioventricular bundle (of His); left bundle branch; Purkinje fibers on surface of left ventricle to apex.

Endothoracic fascia

Connective tissue which attaches the parietal pleura to the thoracic wall

Coronary Arteries (General)

Coronary Arteries: Arise from aortic sinuses (of Valsalva), right and left; first branches of the aorta

What are the histological layers of the cardiac wall?

Endocardium, myocardium, epicardium.

Chordae tendineae

Fibrous attachments from papillary muscles to the leaflets of the atrioventricular valves.

In what layer of the cardiac wall are the coronary arteries and their major branches found?

In the epicardium.

Musculi pectinati

Muscular bundles making ridges in the inner surface of the auricles.

Are the cardiac valves heard best by listening directly over their projection on the surface?

No. Valve sounds are best heard by listening directly over the structure immediately distal to blood flow through the valve.

Cardiac referred pain

Pain fibers from nerve cells in the first four thoracic dorsal root ganglia are distributed to the heart through the visceral branches from the thoracic sympathetic ganglia. These fibers are stimulated by ischemia (lack of blood) which results in pain that is referred to the left side of the chest and the medial surface of the left arm.

Transverse sinus

Part of the pericardial sac located between the atria and the great vessels.

Sternocostal surface of the heart

Principally formed by the right ventricle; that part of the heart facing the sternum, costal cartilages, and ribs. (anterior surface)

No right coronary artery

Rare

What are the contents of the middle mediastinum?

The contents of the middle mediastinum include the contents of the pericardial sac and a few structures in contact with it: - - heart - pericardium - ascending aorta - pulmonary trunk - roots of the lungs - tracheobronchial lymph nodes. In addition, parts of the following are also considered to lie within the middle mediastinum: - superior vena cava - pulmonary veins - azygos vein; phrenic nerves - pericardiacophrenic vessels.

What is the normal "pacemaker" of the heart?

The normal pacemaker of the heart is the sinoatrial node.

Why does a "heart attack" (myocardial infarction) sometimes produce pain along the medial aspect of the arm?

This phenomenon involves a poorly understood entity called "referred pain". One explanation of this occurrence calls attention to the fact that afferent fibers from the heart enter the spinal cord at the same level as those from the medial aspect of the arm. Since the visceral afferent fibers from the heart are presumably only rarely active, impulses set up in these fibers are interpreted by the brain as coming from the more commonly active somatic afferent fibers of the arm

Pericardial Cavity

Transverse sinus (right)- a portion of the pericardial cavity bounded anteriorly by the aorta and pulmonary trunk and posteriorly by the left atrium and the superior vena cava. Formed during development by the breakdown of the dorsal mesocardium between the arterial and venous ends of the heart. Clinical enrichment: Allows vessels to be temporarily clamped during cardiopulmonary bypass. b. Oblique sinus (left)- blind pouch between the left atrium and the posterior part of the pericardium. Bounded on either side by the pulmonary veins. Cul-de-sac posterior to left atrium. Clinical enrichment: Accumulated blood (after surgery) can cause tamponade (compression) of left atrium

Venae cordis minimae

Very small veins which drain blood from the myocardium, opening directly into the right atrium, primarily; also called Thebesian veins or least cardiac veins

Epicardium

Visceral pericardium

Superior Border

a line from the left 2nd costal cartilage to the right 3rd costal cartilage

Inferior Border

a line from the right 6th costal cartilage to the apex.

Posterior surface (base of the heart)

a. Called the "base" because it is opposite the "apex" b. Formed mainly by the superior portions (the atria, mainly left), the inferior portions (ventricles) being part of the diaphragmatic surface c. Great vessels enter and leave the heart at this surface

Inferior (diaphragmatic) surface

a. Formed by both ventricles, but mainly the left b. Rests on the diaphragm which lies between it and the liver and stomach c. Posterior interventricular sulcus separates left and right ventricles

Anterior anatomical surfaces of hearth

a. Formed mainly by right ventricle and right atrium & auricle b. Coronary (atrioventricular) sulcus separates atria from ventricles c. Anterior interventricular sulcus separates left and right ventricles

Pulmonary valve

best heard in the second intercostal space to the left of the sternum

Aortic valve

best heard in the second intercostal space to the right of the sternum

Tricuspid valve

best heard just to left of the lower part of the sternum.

Purkinje fibers

small, terminal conducting fibers from the right and left bundle branches that ramify in the subendocardial layer of the walls of the ventricles. (e)

Sinoatrial node

the pacemaker of the heart. A mass of modified cardiac muscle fibers located in the wall of the right atrium at the junction between the atrium and the superior vena cava, near the upper end of the crista terminalis. (a)

Dominance is determined by

which coronary artery gives rise to the posterior interventricular a.