Anatomy and Physiology: The Heart

Coronary ArteriesBecause the heart is composed primarily of cardiac muscle tissue that continuously contracts and relaxes, it must have a constant supply of oxygen and nutrients. The coronary arteries are the network of blood vessels that carry oxygen- and nutrient-rich blood to the cardiac muscletissue.

Superior Vena Cava The superior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart.

Inferior Vena CavaThe inferior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.

AortaThe aorta is the largest single blood vessel in the body. It is approximately thediameter of your thumb. This vessel carries oxygen-rich blood from the left ventricle to the various parts of the body.

Pulmonary ArteryThe pulmonary artery is the vessel transporting de-oxygenated blood from the right ventricle to the lungs. A common misconception is that all arteries carry oxygen-rich blood. It is more appropriate to classify arteries as vessels carrying blood away from the heart.

Pulmonary VeinThe pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to the left atrium. A common misconception is that all veins carry deoxygenated blood. It is more appropriate to classify veins as vessels carrying blood to the heart.

The Right Side of the Heart The right system receives blood from the veins of the whole body. This is "used" blood,

which is poor in oxygen and rich in carbon dioxide. The right atrium is the first chamber that receives blood. The chamber expands as its muscles relax to fill with blood that has returned from the

body. The blood enters a second muscular chamber called the right ventricle. The right ventricle is one of the heart's two major pumps. Its function is to pump the

blood into the lungs. The lungs restore oxygen to the blood and exchange it with carbon dioxide, which is

exhaled.

The Left Side of the Heart The left system receives blood from the lungs. This blood is now oxygen rich. The oxygen-rich blood returns through veins coming from the lungs (pulmonary veins)

to the heart. It is received from the lungs in the left atrium, the first chamber on the left side. Here, it moves to the left ventricle, a powerful muscular chamber that pumps the blood

back out to the body. The left ventricle is the strongest of the heart's pumps. Its thicker muscles need to

perform contractions powerful enough to force the blood to all parts of thebody.

This strong contraction produces systolic blood pressure (the first and higher number in blood pressure measurement). The lower number (diastolic blood pressure) is measured when the left ventricle relaxes to refill with blood between beats.

Blood leaves the heart through the ascending aorta, the major artery that feeds blood to the entire body

The Valves

Valves are muscular flaps that open and close so blood will flow in the right direction. There are four valves in the heart:

The tricuspid regulates blood flow between the right atrium and the right ventricle. The pulmonary valve opens to allow blood to flow from the right ventricle to the lungs. The mitral valve regulates blood flow between the left atrium and the left ventricle. The aortic valve allows blood to flow from the left ventricle to the ascending aorta

Physiology

Physiology The heart is the muscular organ of the circulatory system that constantly pumps blood throughout the body. Approximately the size of a clenched fist, the heart is composed of cardiac muscle tissue that is very strong and able to contract and relax rhythmically throughout a person's lifetime.Electrical Conduction System

The heart is composed primarily of muscle tissue. A network of nerve fibers coordinates the contraction and relaxation of the cardiac muscle tissue to obtain an efficient, wave-like pumping action of the heart.

The Heart's Electrical System.The heartbeats are triggered and regulated by the conducting system, a network of specialized muscle cells that form an independent electrical system in the heart muscles. These cells areconnected by channels that pass chemically caused electrical impulses.

PhysiologyThe Sinoatrial Node (often called the SA node or sinus node) serves as the natural pacemaker for the heart. Nestled in the upper area of the right atrium, it sends the electrical impulse thattriggers each heartbeat. The impulse spreads through the atria, prompting the cardiac muscletissue to contract in a coordinated wave-like manner.

The impulse that originates from the sinoatrial node strikes the Atrioventricular node (or AVnode) which is situated in the lower portion of the right atrium. The atrioventricular node in turn sends an impulse through the nerve network to the ventricles, initiating the same wave-like contraction of the ventricles.

The electrical network serving the ventricles leaves the atrioventricular node through theRight and Left Bundle Branches. These nerve fibers send impulses that cause the cardiacmuscle tissue to contract.

Physiology1. Sinoatrial node (SAnode)2. Atrioventricular node(AV node)3. Common AV Bundle4. Right & Left BundleBranches

HEART - Rheumatic Fever and Rheumatic Heart Disease

Rheumatic fever and Rheumatic Heart Disease:

Rheumatic fever is an acute inflammation of the connective tissue, particularly of heart and joints due to immunological reaction.

It is seen mainly in children (5 to 15 years of age) but adults may suffer the first attack.

Etiopathogenesis:

Disease follows 1-5 weeks after pharyngeal infection by Group A beta -Hemolytic Streptococcus.

There is raised Anti-streptolysin-O titre (ASO titre) in blood.

Hence, the disease is thought to be due to cross-reaction between "Antibodies to streptococcal antigen” and “Cardiac tissue antigen” (which is similar to streptococcal antigen).

The initiating beta-hemolytic streptococcal infection of the throat, introduces the streptococcal antigens into the body and may also activate cytotoxic T-cells.

These antigens lead to the production of antibodies to various antigenic components of the streptococcus, which can cross react with certain cardiac antigens, including those from the myocyte sarcoplasma and from the glycoproteins of the valves.

This may be the mechanism for the production of the acute inflammation of the heart in acute rheumatic fever that involves all cardiac layers (endocarditis, myocarditis, and pericarditis).

This inflammation becomes apparent after a latent period of 2 to 3 weeks.

This may progress to chronic stenosis or insufficiency of the valves.

Clinically, the patients give the history of fever, sore throat followed by recovery.

After about two weeks, there is appearance of the symptoms of cardiac involvement and/ or migratory large joint polyarthritis, skin involvement (erythema marginatum) and subcutaneous nodule.

Some patients may develop Sydenham chorea, a neurologic disorder with rapid, involuntary, purposeless movement.

Repeated attacks or severe first attack causes chronic rheumatic heart disease leading to congestive cardiac failure.

Pathology:

Lesion develops in three stages:

1. Stage of exudation (edema with inflammatory cells) with fibrinoid necrosis.

2. Stage of cellular proliferation with formation of Aschoff body.

3. Stage of healing by fibrosis.

Aschoff body:

It is the characteristic lesion of the Rheumatic disease.

It consists of:

1. Cental fibrinoid necrosis ;

2. Surrounded by inflammatory cells and large, mono or multinucleated cells with transverse chromatin (Caterpillar cell or Anitschkow myocyte) ;

3. Fibroblasts encircling the above elements.

Aschoff bodies are situated on one side of the small arteries and are characteristically seen in the myocardium.

Lesions :

- Extracardiac Rheumatic Lesions:

1. Joints - Larger joints are involved. Example: knee, ankle, elbow, wrist, shoulder and hip joints.

Aschoff bodies are formed in the synovial membrane, capsule, ligament etc. with serofibrinous effusion.

2. Serous membranes with effusion.

3. Skin- Erythema marginatum.

4. Subcutaneous tissue -Rheumatic nodule mainly seen over the bony prominences. Example: mastoid, knuckle, elbow, patella, scapular margin etc.

- Cardiac Rheumatic Lesions:

Heart (Pancarditis) - involves pericardium, myocardium and endocardium (valvular and mural).

Pericardium:

Grossly, due to acute fibrinous inflammation, pericardium loses its shiny, glossy appearance and becomes rough.

Sticky fibrinous exudate binds two layers of pericardium and on separation the rough surface shows “bread & butter” appearance.

Occasionally, there is a small amount of serofibrinous exudate in the pericardial sac.

Microscopic appearance :

Loss of endothelium with deposition of inflammatory cells - lymphocytes, plasma cells and occasionally polymorphs.

An occasional subpericardial Aschoff body may be present.

Fate:

1. Complete resolution

2. Organization with:

-i) Adhesion between two layers of pericardium (Adhesive pericarditis).

-ii) Adhesive pericarditis with adhesion to mediastinal structures (Adhesive mediastino-pericarditis).

-iii) Milk spot on the anterior surface of the left ventricle.

It is an unresolved patch of rheumatic pericarditis healed by organization.

Myocardium:

Aschoff bodies the characteristic lesion of rheumatic disease, is typically seen in the loose connective tissue of the myocardium, located characteristically near a small blood vessel.

Myocardial fibers are separated by edema and infiltrated with inflammatory cells .

In acute phase of exudation, heart is enlarged with functional disorder.

Later, Aschoff bodies are formed as minute white specks under endocardium, particularly in the left side of the heart at the base of the interventricular septum.

Aschoff bodies are present in the connective tissue between the muscle fibres and cause secondary degeneration of the muscles.

Aschoff bodies are healed up by fibrosis and myocardium is riddled with scarred areas resulting in myocardial failure.

Endocardium:

1. Mural endocardium, particularly in the posterior wall of the left atrium, just above the mitral

valve, become rough, thick and later on scarred (MacCallum’s patch).

This is due to subendocardial aggregation of Aschoff bodies followed by fibrosis.

2. Valvular endocardium:

Most harmful effect of rheumatic disease is due to involvement of cardiac valves.

Mitral valve is most commonly affected, mainly in women, followed by aortic valve, mainly in men.

Tricuspid valve is rarely affected.

Pulmonary valve is practically never affected.

Inflammed valve cusps become edematous, thickened and there is formation of Aschoff bodies in the subendothelial connective tissue.

Continued work of the inflamed valves causes loss of endothelium due to trauma along the line of contact (a few millimeters above the free margin of the cusps).

On this raw surface platelets and fibrin are deposited forming minute, pale thrombi called rheumatic vegetations.

In course of time vegetations are organized and covered by the growth of the adjacent endothelium.

Rheumatic Vegetations:

1. Tiny (size of a pin’s head), sessile arranged in a row and firmly fixed with the underlying tissue, hence there is no embolism.

2. These are situated in the valve cusp, a few millimeters away from the free margin (this is the most traumatized area).

3. Vegetations may be situated on the auricular surface of mitral valve and ventricular surface of the aortic valve.

4. These are organized and endothelialized pale thrombi.

Aschoff bodies are also found in the chordae tendineae, which become fibrosed and shortened.

During acute stage, inflamed edges of cusps adhere together and later become fibrosed causing narrowing or stenosis.

Repeated attack of rheumatic fever causes repeated injury to valves and chordae tendineae, which become fibrosed, thickened and shortened.

Valve cusps appear as diaphragm with a central slit called ‘button hole’ type of mitral stenosis, commonly seen in adults.

Fusion of cusps with shortening of chordae tendineae produce ‘funnel shaped’ mitral stenosis with oval orifice at the apex of the funnel.

This is commonly seen in children.