User:Daniel Breslauer/Cardiology

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This article about Cardiology is still under development.

Anatomy and Physiology of the Heart

Basic Cardiac Anatomy Part 1: Blood Flow into and out of the Heart

From an anatomical point of view the human heart is composed of four compartments or chambers. An easy way to remember the compartments of the heart is to imagine the heart composed of two apartments like a duplex. There are two halves to the heart separated by a septum (wall). Each compartment is composed of an atrium (the entrance) and a ventricle (living room). When visitors (blood) arrives at either of the two apartments, it enters the atrium through the doors (valves), then moves through to the living room (ventricle) once again through doors (valves).

Blood arrives at the heart through the veins and leaves via the arteries. For example, when blood returns to the heart after travelling around the entire body, it enters through either the superior or the inferior vena cava. When the blood returns to the left atrium after being oxygenated in the lungs, it does so through the pulmonary veins.

The larger of the two chambers is the left side, because of the greater distance the blood has to travel once expulsed from the heart, the entire body in the left ventricle and the lungs in the right ventricle, the left myocardium is a lot more developed than the right side.

Roughly speaking, blood circulates in two ways around the body. One way is the systemic circulation and the other is the pulmonary circulation. The total circulation follows a figure of eight pattern (8) with the heart in the centre between the two loops. The lungs are supplied by the uppermost loop (pulmonary) and the rest of the body is supplied by through the lower loop (systemic). The blood leaves the heart through the aorta (through the aortic valve) and travels to the upper and lower portions of the body. Blood returns to right atrium via either the inferior or superior vena cava. From the right atrium, the blood empties into the right heart ventricle through the opening of the tricuspid valve; the blood leaves the right ventricle through the pulmonary valve and travels through the pulmonary arteries to the left and right lungs where it is oxygenated. After oxygenation, the blood returns to the left atrium through the pulmonary veins and it passes through the bicuspid (or mitral) valve to the left ventricle. This process is repeated about 60 times per minute, once for each beat of the heart.

Basic Cardiac Anatomy Part 2: Circulation

• 1 Left pulmonary vein
• 2 Right pulmonary vein
• 3 Left atrium
• 4 Mitral valve
• 5 Left ventricle
• 6 Aortic valve (also: Aortic semilunar valve)
• 7 Aorta Ascendens
• 8 Aortic bow
• 9 Aorta Descendens
• 10 Vena Cava Inferior (also: ICV)
• 11 Vena Cava Superior (also: SCV)
• 12 Right atrium
• 13 Tricuspid valve
• 14 Right ventricle
• 15 Pulmonalis valve (also: Pulmonary semilunar valve)
• 16 Truncus pulmonalis
• 17 Right pulmonary artery
• 18 Left pulmonary artery
• 19 Interventricular septum
• 20 Interatrial septum

Note: The major sidebranches of the aorta (around the aortic bow) have not been shown. Many important vessels (arteries supplying the head, neck, and upper limbs) originate in the aortic bow.

We have learned that the heart consists of two atria (singular atrium) and two ventricula (in English, ventricles or the singular, ventricle.)and that blood circulates around the body in two distinct ways. We will now follow the route blood takes when it travels through the heart, beginning with the blood from the lungs.

• 1. Blood is oxygenated in the lungs. Waste materials (Carbon dioxide, CO₂) are released and Oxygen, O₂ is absorbed by the RBCs (Red Blood Cells).
• 2. The oxygenated blood now travels through the pulmonary veins (venae pulmonales) to the left atrium.
• 3. During the diastolic phase (Diastole: relaxation of the heart), the blood enters the left ventricle through the mitral valve.
• 4. During the systolic phase, (Systole: Contraction of the heart), the heart muscle contracts and the blood is pushed into the aorta ascendens (ascending aorta) through the aortic valve.
• 5. From the aortic bow and the aorta descendens (descending aorta), the blood is spread to smaller arteries which supply every part of the body with fresh oxygenated blood.
• 6. Blood passes through capillaries (hair vessels) where gas exchange between the tissues and the RBCs takes place. The RBCs release oxygen into the tissues and absorb carbon dioxide which will be released again in the lungs.
• 7. The blood leaves the capillaries and flows back into veins.
• 8. The veins combine in the vena cava superior (upper body, above the heart) or vena cava inferior (lower body, under the heart).
• 9. The vena cava superior and inferior both end in the right atrium.
• 10. During diastole, the blood enters the right ventricle through the tricuspid valve.
• 11. During systole, the blood is pushed into the main pulmonary artery (truncus pulmonalis) through the pulmonalis valve.
• 12. Via the lung arteries, the blood reaches the lung capillaries where gas exchange between air and RBCs takes place.
• 13. Back to step 1.

Basic Cardiac Anatomy Part 3: Blood Supply of the Heart

• MB = Main Branch
• LRAD = Left Ramus Anterior Descendens
• Cx = Circumflex artery
• RCA = Right Coronary Artery
• RDP = Ramus Descendens Posterior

Note: Only the most basic arteries comprising the coronary arterial system are shown here. There are many small branches to each of these arteries; this is only a basic description of the coronary system.

The heart is always working and therefore, needs a continuous uninterrupted supply of fresh oxygenated blood. A system of vessels surrounding the heart, known as the coronary arteries (or simply the coronaries) supply the heart with all the blood it needs. The coronary arteries originate from the aorta ascendens just above the aortic valve. There are two coronaries, one of which splits into two separate coronaries just after its origin; in fact, we could also say that we have three coronaries.

• On the right side, the right coronary artery, runs through the line known as sulcus coronarius (which lies approximately above the border between the right atrium and ventricle) all the way until the back of the heart where it ends in the long interventricular line. Its latter half is known as the Ramus Descendens Posterior. A few centimeters after its origin in the aorta ascendens, the right coronary has a small sidebranch known as the sinus node artery, this supplies the sinus node with blood, and after that, another small branch supplies the front side of the right ventricle with blood.
• The left side of the heart, is more muscular since it needs to push the blood with greater force into the aorta ascendens than the right ventricle needs to push blood into the truncus pulmonalis. This is because the left side of the heart needs to supply every part of the body with blood, from the brain to the fingers and toes.

Basic Cardiac Anatomy Part 4: Electrical Activity of the Heart

The pumping action of the heart is initiated by electrical stimulation of the right atrium, by a small pocket of tissue called the Sino-Atrial (SA) node. From here, electrical current follows a conduction pathway through to the ventricles. From the SA node, current travels through both atrium, stimulating their contraction, before coming to the Atrio-Ventricular (AV ) node at the junction of the atria and ventricles. Here, conduction is slowed to allow proper contraction of the atrium (and thus adequate filling of the ventricles with blood). From the AV node, curent flows to the bundle of His (located just below the AV node). It then flows down the Left and Right Bundle Branches, on either side of the intraventricular septum, and to the Purkinje fibres in the ventricules, which cause ventricular contraction.

Cardiac Pathology

Coronary Artery Disease (CAD)

CAD involves the impairment of blood flow through the coronary arteries. This can have several causes, including atheromas, but muscular spasms (coronary artery spasms); the latter are often the result of cocaine use. CAD is one of the most frequent causes of morbidity and mortality in the western world; it is widely considered to be a 'luxury disease.' In its acute form, it is referred to as acute coronary syndrome (ACS), which includes angina pectoris and myocardial infarction (MI). Treatment of ACS preferably takes place in a specialized Cardiac Care Unit (CCU), where the patient is stabilized and a further course of action is determined, which may be medical or surgical. Surgical options include percutaneous coronary intervention (PCI) and coronary artery bypass grafting (CABG).

Infectious diseases of the heart

Infections of the heart may have various consequences and may require urgent treatment.

Endocarditis

There are two forms of endocarditis. The first is infective endocarditis, which is an infection of the endocardium with bacteria (most commonly streptococci and staphylococci) or fungi. Treatment is medical and occasionally surgical as well. Infective endocarditis occurs in men twice as often as in women.

The other form of endocarditis is noninfective endocarditis. This type of endocarditis is causes by sterile platelet and fibrin thrombi form on cardiac valves and adjacent endocardium.

Both forms of endocarditis may lead to embolization and disrupt cardiac function.

Pericarditis

Pericarditis refers to infection of the pericardium, which may have various causes. An important cause is idiopathic. It is the most common disorder of the pericardium.

Cardiomyopathies

Cardiomyopathies, which are usually present at birth but may only become apparent later in life, result in altered cardiac function. There are several types of cardiomyopathy.

Arrhytmias

Arrhytmias may be the result of various causes, including disorders of the heart's electrical system, cardiac tumors, or metabolical disorders.

Cardiac Tumors

Cardiac tumors may be either primary or metastatic. In cardiological tumors, the difference between benign and malignant tumors is less important than the location and size of the tumor. The most common type of cardiac tumor is myxoma, which is benign, and represents 50% of all primary cardiac tumors. The patient usually dies because the tumor itself physically disturbs the functioning of the heart. When feasible, the tumor is surgically resected; when this is not possible, cardiac tumors are always fatal. When the tumor is metastatic, resecting it might lead to a deterioration in the general health of the patient which may speeden the process of death; therefore, metastatic tumors are almost always fatal.

Tumors may occur in any cardiac tissue. The most common places where benign primary cardiac tumors originate are the myocardium and the endocardium; less common places include the valve tissue, cardiac connective tissue, or pericardium. The physical consequences of tumor growth may include valvular or inflow-outflow tract obstruction, thromboembolism, arrhytmias, or pericardial disorders.

As mentioned previously, 50% of all primary tumors are myxomas. Other benign primary tumors include papillary fibroelastomas, rhabdomyomas, fibromas, hemangiomas, teratomas, lipomas, paragangliomas, and pericardial cysts. Malignant primary tumors include sarcomas, pericardial mesothelioma, and primary lymphomas.

Treatment

Therapeutic options in cardiology include both medical and surgical options. Some methods, such as cardiological interventional radiology, fall in between.

Medical

Medical options include

Surgical

Large surgeries, such as coronary artery bypass grafting (CABG) are carried out by cardiothoracic surgeons, while smaller operations, such as percutaneous coronary intervention (PCI), may be carried out by a cardiologist who specialized in interventional cardiology. Other operations include valvular repair and replacement of valves with synthetic valves, transplantations, and the removal of cardiac tumors.

Subpages (for development)

• User:Daniel Breslauer/Cardiology/Abbreviations

External Links

• The Merck Manual, Section 7: Cardiovascular Disorders
• eMedicine.com, Cardiology section
• TheVirtualHeart.com Excellent interactive page with heart anatomy and arrhythmias information