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Development of the

Dr. W. Kibe

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• The heart precursor cells come from the two regions of the splanchnic mesoderm called the cardiogenic mesoderm. These cells can differentiate into endocardium which lines the heart chamber and valves and the myocardium which forms the musculature of the ventricles and the atria.

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Cardiogenic signals are important in directing this development.

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• The cardiac precursor cells migrate anteriorly towards the midline and fuse into a single heart tube. Fibronectin in the extracellular matrix directs this migration. If this migration event is blocked, cardia bifida results where the two heart primordia remain separated. During fusion, the heart tube is patterned along the anterior/posterior axis for the various regions and chambers of the heart.

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• The heart tube undergoes right-ward looping to change from anterior/posterior polarity to left/right polarity. • The cell fates of the heart chambers are characterized before heart looping but cannot be distinguished until after looping

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• Proper positioning and function of the valves is critical for chamber formation and proper blood flow. The endocardial cushion serves as a makeshift valve until then.

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• At 21 days after conception, the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating. • The human heart beats more than 3.5 billion times in an average lifetime.

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• The human embryonic heart begins beating approximately 21 days after conception, or five weeks after the last normal menstrual period (LMP), which is the date normally used to date pregnancy. The human heart begins beating at a rate near the mother’s, about 75- 80 beats per minute (BPM

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• The embryonic heart rate (EHR) then accelerates linearly for the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, an increase of 100 BPM in the first month.

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• There is no difference in male and female heart rates before birth

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• A (CHD) is a defect in the structure of the heart and great vessels of a newborn. Most heart defects either obstruct blood flow in the heart or vessels near it or cause blood to flow through the heart in an abnormal pattern, although other defects affecting heart rhythm (such as long QT syndrome) can also occur.

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• Heart defects are among the most common birth defects and are the leading cause of birth defect-related deaths.

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• Symptoms and signs are related to the type and severity of the heart defect. Some children have no signs while others may exhibit shortness of breath, , chest pain, syncope, sweating, heart murmur, respiratory infections, underdeveloping of limbs and muscles, poor feeding, or poor growth, build up of blood and fluid in lungs, feet, ankles and legs.

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• Congenital heart defects cause abnormal heart structure resulting in production of certain sounds called heart murmurs. Doctors can simply detect it with stethoscope. However, all heart murmurs are not caused by congenital heart defects. CHD symptoms frequently present early in life, but it's possible for some CHDs to go undetected throughout life.

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• The cause may be due to a genetic predisposition or an environmental exposure during pregnancy. • Known genetic causes of heart disease includes chromosomal abnormalities such as trisomies 21, 13, and 18, as well as a range of newly recognised genetic point mutations, point deletions and other genetic abnormalities as seen in syndromes such as Velo-Cardio-Facial Syndrome, familial ASD with heart block, Alagille syndrome, Noonan syndrome, and many more.

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• 1 Hypoplasia • Hypoplasia can affect the heart, which typically results in the failure of either the right ventricle or the left ventricle to develop adequately, leaving only one side of the heart capable of pumping blood to the body and lungs. Hypoplasia of the heart is rare but is the most serious form of CHD; it is called hypoplastic left heart syndrome when it affects the left side of the heart and hypoplastic right heart syndrome when it affects the right side of the heart.

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• In both conditions, the presence of a patent (and, when hypoplasia affects the right side of the heart, a patent foramen ovale) is vital to the infant's ability to survive until emergency heart surgery can be performed, since without these pathways blood cannot circulate to the body (or lungs, depending on which side of the heart is defective). Hypoplasia of the heart is generally a . • atresia

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• Obstruction defects occur when heart valves, arteries, or veins are abnormally narrow or blocked. Common obstruction defects include pulmonary valve stenosis, stenosis, and coarctation of the aorta, with other types such as stenosis and subaortic stenosis being comparatively rare. Any narrowing or blockage can cause heart enlargement or hypertension.

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• The septum is a wall of tissue which separates the left heart from the right heart. It is comparatively common for defects to exist in the interatrial septum or the interventricular septum, allowing blood to flow from the left side of the heart to the right, reducing the heart's efficiency.

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• Ventricular septal defects are collectively the most common type of CHD, although approximately 30% of adults have a type of called patent foramen ovale. Septal defects may or may not cause cyanosis depending on the severity of the defect.

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• Cyanotic heart defects are called such because they result in cyanosis, a bluish-grey discoloration of the skin due to a lack of oxygen in the body. Such defects include persistent truncus arteriosus, total anomalous pulmonary venous connection, , transposition of the great vessels, and tricuspid

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• Known antenatal environmental factors include maternal infections (Rubella), drugs (alcohol, hydantoin, lithium and thalidomide) and maternal illness (diabetes mellitus, phenylketonuria, and systemic lupus erythematosus).

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• Sometimes CHD improves with no treatment necessary. At other times the defect is so small and does not require any treatment. Most of the time CHD is serious and requires surgery and/or medications.

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• Medications include diuretics, which aid the baby in eliminating water, salts, and digoxin and in strengthening the contraction of the heart. This slows the heartbeat and removes some fluid from tissues.

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• Some defects require surgical procedures to repair as much as possible to restore circulation back to normal. In some cases, multiple surgeries are needed to be performed to help balance the circulation. Interventional now offers patients minimally invasive alternatives to surgery.

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• Device closures can now be treated with a standard transcatheter procedure using a closure device mounted on a balloon catheter.

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• Tetralogy of Fallot (TOF) is a congenital heart defect which is classically understood to involve four anatomical abnormalities (although only three of them are always present). It is the most common cyanotic heart defect, representing 55-70%, and the most common cause of blue baby syndrome.

Create PDF files without this message by purchasing novaPDF printer (http://www.novapdf.com) Tof has 4 malformations:

• 1Pulmonary stenosis • 2 Overriding aorta • 3. ventricular septal defect (VSD) • 4 Right ventricular hypertrophy

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