Recommendation of a Strategy

The Heart

Ken M. Fonghe M.D.ANY Department

Heart

The heart is a pair of valved muscular pumps combined in a single organ

The general shape and orientation of the heart are that of a pyramid that has fallen over and is resting on one of its sides.

Placed in the thoracic cavity, the apex of this pyramid projects forward, downward, and to the left, whereas the base is opposite the apex and faces in a posterior direction

The heart is a hollow muscular organ that is somewhat pyramid shaped and lies within the pericardium in the mediastinum

It is connected at its base to the great blood vessels but otherwise lies free within the pericardium.

Although the fibromuscular framework and conduction tissues of these pumps are structurally interwoven, each pump (the so-called right' and left' hearts) is physiologically separate, and is interposed in series at different points in the double circulation.

Cardiac Orientation

The sides of the pyramid consist of:

a diaphragmatic (inferior) surface on which the pyramid rests;

an anterior (sternocostal) surface oriented anteriorly;

a right pulmonary surface;

a left pulmonary surface

The sternocostal surface is formed mainly by the right atrium and the right ventricle, which are separated from each other by the vertical atrioventricular groove. The right border is formed by the right atrium; the left border, by the left ventricle and part of the left auricle. The right ventricle is separated from the left ventricle by the anterior interventricular groove.

The diaphragmatic surface of the heart is formed mainly by the right and left ventricles separated by the posterior interventricular groove. The inferior surface of the right atrium, into which the inferior vena cava opens, also forms part of this surface.

The apex of the heart, formed by the left ventricle, is directed downward, forward, and to the left. It lies at the level of the fifth left intercostal space, 3.5 in. (9 cm) from the midline. In the region of the apex, the apex beat can usually be seen and palpated in the living patient.

The sternocostal surface is formed mainly by the right atrium and the right ventricle, which are separated from each other by the vertical atrioventricular groove. The right border is formed by the right atrium; the left border, by the left ventricle and part of the left auricle. The right ventricle is separated from the left ventricle by the anterior interventricular groove.

The diaphragmatic surface of the heart is formed mainly by the right and left ventricles separated by the posterior interventricular groove. The inferior surface of the right atrium, into which the inferior vena cava opens, also forms part of this surface.

The apex of the heart, formed by the left ventricle, is directed downward, forward, and to the left. It lies at the level of the fifth left intercostal space, 3.5 in. (9 cm) from the midline. In the region of the apex, the apex beat can usually be seen and palpated in the living patient.

The base of the heart, or the posterior surface, is formed mainly by the left atrium, into which open the four pulmonary veins. The base of the heart lies opposite the apex.

Note that the base of the heart is called the base because the heart is pyramid shaped; the base lies opposite the apex. The heart does not rest on its base; it rests on its diaphragmatic (inferior) surface.

The base of the heart is quadrilateral and directed posteriorly. It consists of: the left atrium; a small portion of the right atrium; the proximal parts of the great veins (superior and inferior venae cavae and the pulmonary veins)

Pericardium

The pericardium is a fibroserous sac that encloses the heart and the roots of the great vessels.

Its function is to restrict excessive movements of the heart as a whole and to serve as a lubricated container in which the different parts of the heart can contract.

The pericardium lies within the middle mediastinum, posterior to the body of the sternum and the second to the sixth costal cartilages and anterior to the fifth to the eighth thoracic vertebrae.

Fibrous Pericardium

The fibrous pericardium is the strong fibrous part of the sac. It is firmly attached below to the central tendon of the diaphragm. It fuses with the outer coats of the great blood vessels passing through itnamely, the aorta, the pulmonary trunk, the superior and inferior venae cavae, and the pulmonary veins. The fibrous pericardium is attached in front to the sternum by the sternopericardial ligaments.

Serous Pericardium

The serous pericardium lines the fibrous pericardium and coats the heart. It is divided into parietal and visceral layers

the parietal layer lines the inner surface of the fibrous

the visceral layer (epicardium) of serous pericardium adheres to the heart and forms its outer covering.

Pericardial Cavity

The slitlike space between the parietal and visceral layers is referred to as the pericardial cavity

Normally, the cavity contains a small amount of tissue fluid (10 or 1550 mL), the pericardial fluid, which acts as a lubricant to facilitate movements of the heart.

Pericardial Fluid

10-50 mL

pale yellow and clear

Protein. A value greater than 3.0 g/dL has a sensitivity of 97% for exudative effusions, but a specificity of only 22% which significantly limits its usefulness. Thus, total protein has no discriminating power in pericardial diagnosis ( Meyers, 1997 ).

Glucose. Pericardial glucose levels less than 60 mg/dL have a diagnostic accuracy of only 36% in identifying pericardial exudates ( Meyers, 1997 ). Values less than 40 mg/dL (< 2.22 mmol/L) are common in bacterial, tuberculous, rheumatic, or malignant effusions.

pH. Pericardial fluid pH may be markedly decreased (< 7.10) in rheumatic or purulent pericarditis. Malignancy, uremia, tuberculosis, and idiopathic disorders may have moderate decreases in the range of 7.20-7.30 ( Kindig, 1983 ).

Lipids. Separation of true chylous from pseudochylous effusions may be facilitated by triglyceride and cholesterol measurements, as well as lipoprotein electrophoresis for chylomicrons

Enzymes. A pericardial fluidlactate dehydrogenase (LD) level greater than 200 U/L has been suggested as a cutoff for pericardial exudates ( Burgess, 2002a ). Moreover, the measurement of LD and creatine kinase in postmortem pericardial fluid within 48 hours of death may be useful in establishing acute myocardial injury in cases where such injury is suspected but cannot be established by the usual histologic methods ( Luna, 1982 ; Stewart, 1984 ). Pericardial fluid levels of CK-MB, myoglobin, and troponin I in postmortem pericardial fluid are also significantly increased in patients with myocardial injury ( Perez-Carceles, 2004 ).

Right Atrium

The right atrium consists of a main cavity and a small outpouching, the auricle.

On the outside of the heart at the junction between the right atrium and the right auricle is a vertical groove, the sulcus terminalis, which on the inside forms a ridge, the crista terminalis.

The main part of the atrium that lies posterior to the ridge is smooth walled and is derived embryologically from the sinus venosus.

The part of the atrium in front of the ridge is roughened or trabeculated by bundles of muscle fibers, the musculi pectinati, which run from the crista terminalis to the auricle.

Openings into the Right Atrium

The superior vena cava opens into the upper part of the right atrium; it has no valve. It returns the blood to the heart from the upper half of the body. The inferior vena cava (larger than the superior vena cava) opens into the lower part of the right atrium; it is guarded by a rudimentary, nonfunctioning valve. It returns the blood to the heart from the lower half of the body.

The coronary sinus, which drains most of the blood from the heart wall, opens into the right atrium between the inferior vena cava and the atrioventricular orifice. It is guarded by a rudimentary, nonfunctioning valve.

The right atrioventricular orifice lies anterior to the inferior vena caval opening and is guarded by the tricuspid valve.

Many small orifices of small veins also drain the wall of the heart and open directly into the right atrium.

Fetal Remnants

The fossa ovalis is a shallow depression, which is the site of the foramen ovale in the fetus

The anulus ovalis forms the upper margin of the fossa. The floor of the fossa represents the persistent septum primum of the heart of the embryo, and the anulus is formed from the lower edge of the septum secundum

Right Ventricle

communicates with the right atrium through the atrioventricular orifice and with the pulmonary trunk through the pulmonary orifice

extends from the right atrioventricular (tricuspid) orifice nearly to the cardiac apex

ascends to the left to become the infundibulum, or conus arteriosus, reaching the pulmonary orifice and supporting the cusps of the pulmonary valve

thicker than those of the right atrium

The projecting ridges give the ventricular wall a spongelike appearance and are known as trabeculae carneae

The first type comprises the papillary muscles, which project inward, being attached by their bases to the ventricular wall; their apices are connected by fibrous chords (the chordae tendineae) to the cusps of the tricuspid valve (Fig. 3-37).

The second type is attached at the ends to the ventricular wall, being free in the middle. One of these, the moderator band, crosses the ventricular cavity from the septal to the anterior wall. It conveys the right branch of the atrioventricular bundle, which is part of the conducting system of the heart.

The third type is simply composed of prominent ridges

Left Atrium

Situated behind the right atrium and forms the greater part of the base or the posterior surface of the heart

Behind it lies the oblique sinus of the serous pericardium, and the fibrous pericardium separates it from the esophagus

The interior of the left atrium is smooth, but the left auricle possesses muscular ridges as in the right auricle

Openings of the Left Atrium

The four pulmonary veins, two from each lung, open through the posterior wall and have no valves.

The left atrioventricular orifice is guarded by the mitral valve.

The two thicker-walled ventricles consist of three interdigitating muscle layers:

the deep sinospiral

the superficial sinospiral

superficial bulbospiral muscles

Components of the myocardium. The outer muscle layers pull the apex of the heart toward the base. The inner circumferential layers constrict the lumen, particularly of the left ventricle.

Left Ventricle

Communicates with the left atrium through the atrioventricular orifice and with the aorta through the aortic orifice

The walls of the left ventricle are three times thicker than those of the right ventricle. (The left intraventricular blood pressure is six times higher than that inside the right ventricle.)

In cross section, the left ventricle is circular; the right is crescentic because of the bulging of the ventricular septum into the cavity of the right ventricle.

There are well-developed trabeculae carneae, two large papillary muscles, but no moderator band. The part of the ventricle below the aortic orifice is called the aortic vestibule.

Valves

Tricuspid valve

Pulmonary valve

Bicuspid valve

Aortic valve

Tricuspid valve

The right atrioventricular orifice is closed during ventricular contraction by the tricuspid valve (right atrioventricular valve), which is so-named because it usually consists of three cusps or leaflets

The base of each cusp is secured to the fibrous ring that surrounds the atrioventricular orifice. This fibrous ring helps to maintain the shape of the opening. The cusps are continuous with each other near their bases at sites termed commissures.

The naming of the three cusps, the anterior, septal, and posterior cusps, is based on their relative position in the right ventricle. The free margins of the cusps are attached to the chordae tendineae, which arise from the tips of the papillary muscles.

Bicuspid Valve

The left atrioventricular orifice opens into the posterior right side of the superior part of the left ventricle. It is closed during ventricular contraction by the mitral valve (left atrioventricular valve), which is also referred to as the bicuspid valve because it has two cusps, the anterior and posterior cusps

The bases of the cusps are secured to a fibrous ring surrounding the opening, and the cusps are continuous with each other at the commissures. The coordinated action of the papillary muscles and chordae tendineae is as described for the right ventricle.

Pulmonary Valve

The pulmonary valve guards the pulmonary orifice and consists of three semilunar cusps formed by folds of endocardium with some connective tissue enclosed.

At the apex of the infundibulum, the outflow tract of the right ventricle, the opening into the pulmonary trunk is closed by the pulmonary valve

The cusps are named the left, right and anterior semilunar cusps, relative to their fetal position before rotation of the outflow tracks from the ventricles is complete.

Each cusp forms a pocket-like sinus-a dilation in the wall of the initial portion of the pulmonary trunk. After ventricular contraction, the recoil of blood fills these pulmonary sinuses and forces the cusps closed. This prevents blood in the pulmonary trunk from refilling the right ventricle.

Aortic valve

The aortic vestibule, or outflow tract of the left ventricle, is continuous superiorly with the ascending aorta.The opening from the left ventricle into the aorta is closed by the aortic valve. This valve is similar in structure to the pulmonary valve. It consists of three semilunar cusps with the free edge of each projecting upward into the lumen of the ascending aorta Between the semilunar cusps and the wall of the ascending aorta are pocket-like sinuses-the right, left, and posterior aortic sinuses. The right and left coronary arteries originate from the right and left aortic sinuses. Because of this, the posterior aortic sinus and cusp are sometimes referred to as the noncoronary sinus and cusp.

Position of the tricuspid and pulmonary valves. B. Mitral cusps with valve open. C. Mitral cusps with valve closed. D. Semilunar cusps of the aortic valve. E. Cross section of the ventricles of the heart. F. Path taken by the blood through the heart. G. Path taken by the cardiac impulse from the sinuatrial node to the Purkinje network. H. Fibrous skeleton of the heart.

Aortic valve

The aortic vestibule, or outflow tract of the left ventricle, is continuous superiorly with the ascending aorta.

The opening from the left ventricle into the aorta is closed by the aortic valve.

This valve is similar in structure to the pulmonary valve. It consists of three semilunar cusps with the free edge of each projecting upward into the lumen of the ascending aorta

Between the semilunar cusps and the wall of the ascending aorta are pocket-like sinuses-the right, left, and posterior aortic sinuses. The right and left coronary arteries originate from the right and left aortic sinuses. Because of this, the posterior aortic sinus and cusp are sometimes referred to as the noncoronary sinus and cusp.

Position of the tricuspid and pulmonary valves. B. Mitral cusps with valve open. C. Mitral cusps with valve closed. D. Semilunar cusps of the aortic valve. E. Cross section of the ventricles of the heart. F. Path taken by the blood through the heart. G. Path taken by the cardiac impulse from the sinuatrial node to the Purkinje network. H. Fibrous skeleton of the heart.

The functioning of the aortic valve is similar to that of the pulmonary valve with one important additional process: as blood recoils after ventricular contraction and fills the aortic sinuses, it is automatically forced into the coronary arteries because these vessels originate from the right and left aortic sinuses.

Interatrial septum

Interventricular septum

Layers of the Heart Wall

The endocardium, a simple squamous epithelium and underlying subendothelial connective tissue, lines the lumen of the heart.

The thick middle layer of the heart (the myocardium) is composed of cardiac muscle cells.

Epicardium, the outermost layer of the heart wall, is also called the visceral layer of the pericardium (composed of a simple squamous epithelium known as a mesothelium).

Cardiac Skeleton

The cardiac skeleton, composed of dense connective tissue, includes three main components: The annuli fibrosi, formed around the base of the aorta, pulmonary artery, and the atrioventricular orifices The trigonum fibrosum, formed primarily in the vicinity of the cuspal area of the aortic valve The septum membranaceum, constituting the upper portion of the interventricular septum In addition to providing a structural framework for the heart and attachment sites for the cardiac muscle, the cardiac skeleton provides a discontinuity between the myocardia of the atria and ventricles, thus ensuring a rhythmic and cyclic beating of the heart, controlled by the conduction mechanism of the atrioventricular bundles.

Coronary Circulation

Arterial

Venous

Right Coronary Artery

right aortic sinus of the ascending aorta right coronary artery atrial branch sinu-atrial nodal branch SA node right marginal branch apex of the heart small branch to the atrioventricular node before giving off its final major branch, the posterior interventricular branch, which lies in the posterior interventricular sulcus.

The right coronary artery supplies the right atrium and right ventricle, the sinu-atrial and atrioventricular nodes, the interatrial septum, a portion of the left atrium, the posteroinferior one-third of the interventricular septum, and a portion of the posterior part of the left ventricle.

Left Coronary Artery

left aortic sinus of the ascending aorta left coronary artery two terminal branches: anterior interventricular and the circumflex

the anterior interventricular branch (left anterior descending artery-LAD), which continues around the left side of the pulmonary trunk and descends obliquely toward the apex of the heart in the anterior interventricular sulcus - during its course, one or two large diagonal branches may arise and descend diagonally across the anterior surface of the left ventricle

the circumflex branch, which courses toward the left, in the coronary sulcus and onto the base/diaphragmatic surface of the heart and usually ends before reaching the posterior interventricular sulcus-a large branch, the left marginal artery, usually arises from it and continues across the rounded obtuse margin of the heart.

The distribution pattern of the left coronary artery enables it to supply most of the left atrium and left ventricle, and most of the interventricular septum, including the atrioventricular bundle and its branches.

Several major variations in the basic distribution patterns of the coronary arteries occur: The distribution pattern described for both right and left coronary arteries is the most common and consists of a right dominant coronary artery. This means that the posterior interventricular branch arises from the right coronary artery. The right coronary artery therefore supplies a large portion of the posterior wall of the left ventricle and the circumflex branch of the left coronary artery is relatively small. In contrast, in hearts with a left dominant coronary artery, the posterior interventricular branch arises from an enlarged circumflex branch and supplies most of the posterior wall of the left ventricle.Another point of variation relates to the arterial supply to the sinu-atrial and atrioventricular nodes. In most cases, these two structures are supplied by the right coronary artery. However, vessels from the circumflex branch of the left coronary artery occasionally supply these structures.

Cardiac Veins

The coronary sinus receives four major tributaries:

the great cardiac vein

Middle cardiac vein

Small cardiac vein

posterior cardiac vein

The great cardiac vein begins at the apex of the heart. It ascends in the anterior interventricular sulcus, where it is related to the anterior interventricular artery and is often termed the anterior interventricular vein. Reaching the coronary sulcus, the great cardiac vein turns to the left and continues onto the base/diaphragmatic surface of the heart. At this point, it is associated with the circumflex branch of the left coronary artery. Continuing along its path in the coronary sulcus, the great cardiac vein gradually enlarges to form the coronary sinus, which enters the right atrium

The middle cardiac vein (posterior interventricular vein) begins near the apex of the heart and ascends in the posterior interventricular sulcus toward the coronary sinus. It is associated with the posterior interventricular branch of the right or left coronary artery throughout its course.

The small cardiac vein begins in the lower anterior section of the coronary sulcus between the right atrium and right ventricle. It continues in this groove onto the base/diaphragmatic surface of the heart where it enters the coronary sinus at its atrial end. It is a companion of the right coronary artery throughout its course and may receive the right marginal vein. This small vein accompanies the marginal branch of the right coronary artery along the acute margin of the heart. If the right marginal vein does not join the small cardiac vein, it enters the right atrium directly.

The posterior cardiac vein lies on the posterior surface of the left ventricle just to the left of the middle cardiac vein. It either enters the coronary sinus directly or joins the great cardiac vein.

Other Cardiac Veins

The anterior veins of right ventricle (anterior cardiac veins) are small veins that arise on the anterior surface of the right ventricle. They cross the coronary sulcus and enter the anterior wall of the right atrium. They drain the anterior portion of the right ventricle. The right marginal vein may be part of this group if it does not enter the small cardiac vein.

A group of smallest cardiac veins (venae cordis minimae or veins of Thebesius) have also been described. Draining directly into the cardiac chambers, they are numerous in the right atrium and right ventricle, are occasionally associated with the left atrium, and are rarely associated with the left ventricle.

Lymphatics

brachiocephalic nodes, anterior to the brachiocephalic veins;

tracheobronchial nodes, at the inferior end of the trachea

Conduction System

the sinu-atrial node (SA)

the atrioventricular node (AV)

the atrioventricular bundle with its right and left bundle branches

the subendocardial plexus of conduction cells (the Purkinje fibers)

SA node

Impulses begin

the cardiac pacemaker

superior end of the crista terminalis at the junction of the superior vena cava and the right atrium

junction between the parts of the right atrium derived from the embryonic sinus venosus and the atrium proper.

The excitation signals generated by the sinu-atrial node spread across the atria, causing the muscle to contract.

AV node

near the opening of the coronary sinus, close to the attachment of the septal cusp of the tricuspid valve, and within the atrioventricular septum

near the opening of the coronary sinus, close to the attachment of the septal cusp of the tricuspid valve, and within the atrioventricular septum

AV bundle

direct continuation of the atrioventricular node

follows along the lower border of the membranous part of the interventricular septum before splitting into right and left bundles

The right bundle branch continues on the right side of the interventricular septum toward the apex of the right ventricle. From the septum it enters the septomarginal trabecula to reach the base of the anterior papillary muscle. At this point, it divides and is continuous with the final component of the cardiac conduction system, the subendocardial plexus of ventricular conduction cells or Purkinje fibers. This network of specialized cells spreads throughout the ventricle to supply ventricular musculature including the papillary muscles

The left bundle branch passes to the left side of the muscular interventricular septum and descends to the apex of the left ventricle. Along its course it gives off branches that eventually become continuous with the subendocardial plexus of conduction cells (Purkinje fibers). As with the right side, this network of specialized cells spreads the excitation impulses throughout the ventricle.

Innervation

Sympathetic (cervical and upper portions of thoracic sympathetic ganglia)

Parasympathetic (vagus)

Branches from both the parasympathetic and sympathetic systems contribute to the formation of the cardiac plexus.

This plexus consists of a superficial part, inferior to the aortic arch and between it and the pulmonary trunk, and a deep part, between the aortic arch and the tracheal bifurcation.

The postganglionic sympathetic fibers terminate on the sinuatrial and atrioventricular nodes, on cardiac muscle fibers, and on the coronary arteries. Activation of these nerves results in cardiac acceleration, increased force of contraction of the cardiac muscle, and dilatation of the coronary arteries. The postganglionic parasympathetic fibers terminate on the sinuatrial and atrioventricular nodes and on the coronary arteries. Activation of the parasympathetic nerves results in a reduction in the rate and force of contraction of the heart and a constriction of the coronary arteries.

Excitation Contraction Coupling of the Cardiac Muscle

Action potential spreads into the interior of cardiac muscle fiber, along the membrane of T tubules. The T tubule action potentials act on sarcoplasmic reticulum Calcium is released into the myofibril which catalyzes chemical reaction that promotes the pulling/sliding action of actin and myosin filaments contraction

Extra calcium ions also diffuses into the sarcoplasm from the T tubules themselves at the time of the action potential.Openings of the T tubules pass directly through the cardiac cell membrane into the extracellular spaces surrounding the cell, allowing the samce extracellular fluid that is in cardiac muscle interstitium to percolate through the T tubules as well.(non in the skeletal muscle) the contraction of cardiac muscle is affected by the extracellular calcium.At the end of the plateau, the influx of calcium is shut off, the calcium in the sarcoplasm is pumped back into the sarcoplasmic reticulum and into the T tubules/extracellular fluid, them the contraction ceases until the new action potential occurs.

M

Duration of Contraction

0.2 seconds in atrial muscle

0.3 seconds in ventricular muscle

Cardiac muscle begins to contract a few milliseconds after the action potential begins and continues to contract until a few milliseconds after the action potential ends.

Action Potentials of Cardiac Muscle

Ventricle: about ave 105 mV

Rise from -85mV to about 20mV (in between beats)

After the initial spike, the membrane remains depolarized for about 0.2 second, exhibiting a plateau, followed at the end of plateau by repolarization.

The presence of plateau in the action potential causes ventricular contraction to last as much as 15 times as long in cardiac muscle as in skeletal muscle.

What Causes the long potential and the Plateau?

Calcium Sodium Channels (slow)

Decrease of the permeability of the potassium ions after the onset of action potential

Velocity of Signal Conduction in Cardiac Muscle

Atrial and ventricular fibers: 0.3 0.5 m/s or about 1/250 the velocity of the very large nerve fibers and 1/10 the velocity of skeletal muscle fiber.

Purkinje fibers: 4 m/s

The normal refractory period of the ventricle is 0.25 0.30 seconds

Relative refractory period (ventricle): 0.05 seconds

Atrial muscle: 0.15 seconds

Cardiac Cycle

Are cardiac events from the beginning of one heartbeat to the beginning of the next.

Passage of impulse from atria to ventricles: more than 0.1 second to allow atria to pump ahead of ventricular contraction, therefore pumping the blood to the ventricles before the stronger ventricular contraction begins.

The atria will serve as primer pumps

Isovolumetric contraction

Begins at diastole

The atria filled the ventricle with blood (end diastolic volume: 140cc)

On excitation, the ventricle contracts, the pressure rises, and the valves close.

Since valves are closed, no blood can be ejected from the ventricles (isovolumetric)

Ventricular Ejection

The aortic valve opens when the left ventricular pressure exceeds the pressure of the aorta.

Blood is ejected into the aorta, the volume of the left ventricle is decreased.

The volume remaining in the left ventricle is called end systolic volume.

Isovolumetric relaxation

The ventricle relaxes.

When the ventricular pressure decreases to less than aortic pressure, the aortic valve closes.

All valves are closed volume is constant (isovolumetric)

Ventricular filling

Once the ventricular pressure decreases to less than atrial pressure the AV valve opens ventricular filling up to about 140cc

Frank Starling Law

The greater the heart muscle is stretched, the greater the force of contraction, thus the greater the quantity of blood pumped into the aorta.

Within physiologic limits, the heart pumps all the blood retured to it by the way of the veins.

Pressure Changes in the Atria

a wave: atrial contraction

Right atrium: 4 6 mmHg

Left atrium: 7 8 mmHg

c wave: slight backflow of blood into the atria at the onset of ventricular contraction but mainly by bulging of the AV valves backward to the atria due to increasing pressure of the ventricles

v wave: slow flow of the blood into the atria from the veins

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