The Heart | Shevet
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The Heart
As we work with children who have holes in their heart, our community takes an active interest in pediatric cardiology. On the bookshelf in our office is a concise guide to the science of the issue, created by our volunteer Ellen, a nursing student; we thought it would be helpful to have it sitting on our virtual shelf as well.
Catalogue of Heart Defects
Cardiology 101
Before addressing the defects found in cardiology, one must first understand how a healthy heart functions.
The heart is a pump that constantly supplies the body with oxygen and nutrients via the blood supply. There are four chambers of the heart: a right atrium, a right ventricle, a left atrium and a left ventricle.
First, deoxygenated blood (blood without oxygen) is carried from the body through the Inferior and Superior Vena Cava. From these vessels, the blood is dumped into the Right Atrium of the heart. The atria serve as preliminary holding chambers; i.e. the main pumping chambers are the ventricles, and the atria hold the blood on standby before pumping it into the ventricles. Anyway, blood from the Right Atrium goes into the Right Ventricle from which the blood is pumped to the lungs via the Pulmonary Artery to get oxygenated (i.e. to get oxygen). Once oxygenated at the lungs, the blood returns to the heart via the Pulmonary Veins, and is dumped into the Left Atrium. From there, the blood is pumped into the Left Ventricle, and then is sent out to the body via a blood vessel called the Aorta. The blood travels throughout the body, oxygenating and nourishing the tissues, and then returns to the heart where the cycle starts all over again.
Defects can occur in any of the above structures or tissues.
In addition to the mechanisms and structures mentioned above, there are four major valves in the heart. These valves separate structures that need to allow the gradual, not sudden, passage of blood. Hence, the valves allow a measured amount of blood to pass through to these structures. The Tricuspid Valve separates the Right Atrium from the Right Ventricle, the Pulmonary Valve separates the Right Ventricle from the Pulmonary Artery, the Mitral Valve separates the Pulmonary Veins from the Left Atrium, and the Aortic Valve separates the Left Ventricle from the Aorta. Defects involving these valves are common; the valves can be too narrow, broken, or completely absent.
Lastly, an important aspect of pediatric cardiology involves fetal cardiology, which is the way the heart functions in utero. In utero, the child’s heart has two structures that disappear at birth: the Foramen Ovale and the Ductus Arteriosus. Since the child cannot breathe yet on its own without access to air, oxygen is supplied by the mother via the placenta. These structures allow blood to bypass the lungs. More specifically, the Foramen Ovale is a hole between the Right and Left Atria that allows blood to bypass the right side of the heart (where it would be sent to the lungs) and sends it directly to the left side of the heart. The Ductus Arteriosus is a structure connecting the Pulmonary Artery to the Aorta. Again, this shunts blood away from the lungs, and out to the body. Both of these holes should snap shut and should be fully sealed within 24 hours after birth; complications arise if they remain open. The patency of these structures qualifies as a cardiac defect.
 
 
Cardiac defects can occur in any of the above mentioned structures, involving broken, ineffective, or missing cardiac structures. These will be explained in detail in the following pages, and you may also consult the glossary for definitions of cardiac vocabulary.
 
 
1. Aortic Stenosis (AS)/Aortic Valvular Stenosis (AVS)
Aortic Stenosis (also called AS) refers to a condition in which there is a blockage preventing blood from traveling through the Left Ventricle to the Aorta. The blockage can be caused by a variety of reasons, including muscular obstructions below the valve, a narrowing of the aorta immediately after the valve, or, most often, the aortic valve itself is the cause. This condition is known as Aortic Valvular Stenosis (AVS).
The aortic valve is composed of three cusps (or leaflets) that open and shut as the heart pumps; if these leaflets do not open and close properly, a blockage may occur. As a result of the additional workload, the left ventricle will often hypertrophy (thicken) in order to provide the additional strength to eject the blood. Treatment depends on the severity of the defect. See illustration below.
 
 
2. Atrial Septal Defect (ASD)
There are two atria in the heart; one on the right and one on the left. The right atrium carries deoxygenated blood and the left atrium carries oxygenated blood. An ASD is when there is a hole between these two atria, resulting in a mixing of oxygenated and deoxygenated blood. See illustration below.
 
 
As you can see, more blood flows from left-to-right than right-to-left. This is because the pressure gradient is higher on the left side because it pumps blood to the entire body. As a result, more blood flows to the lungs than is normal, and respiratory conditions such as pulmonary hypertension (high blood pressure in the lungs) may emerge. Surgery for this procedure usually has no complications, and normal activity may be resumed following a successful surgery.
 
3. Atrioventricular Septal Defect (or AV Canal Defect) 
This defect is common in children with Down’s Syndrome. An Atrioventricular Septal Defect is when certain cardiac structures (known as endocardial cushions) fail to develop in utero. These structures divide the heart into four chambers, and without them, there is a tremendous amount of oxygenated and deoxygenated blood cross-over. See illustration below.
With this defect, a child may have absent tissue between the atria, the ventricles, or both. The range of severity of this defect merits a range of treatment.
 
4. Coarctation of the Aorta
Coarctation of the Aorta is the narrowing of the descending aorta . Some have speculated that this defect is caused by scar tissue narrowing the aorta during the closing of the ductus arteriosus. Blood flow to the lower extremities is therefore reduced, and children with this defect will often exhibit high blood pressure in the upper extremities (arms), and low blood pressure in the lower extremities (legs). See illustration below.
 
5. Ebstein's Anomaly
 
Ebstein’s Anomaly is a defect in the tricuspid valve of the heart, which separates the right atrium from the right ventricle. Because the three leaflets of the valve are deformed, they do not effectively seal the atrium from the ventricle. As a result, blood leaks backwards into the atrium rather than being pumped through the ventricle. The right atrium becomes enlarged, and, in severe cases, congestive heart failure may follow. Due to the increased pressure in the atrium, at birth the Patent Foramen Ovale (PFO) often remains open, leading to an Atrial Septal Defect. (The Foramen Ovale is a fetal circulatory structure which shunts blood from the right atrium to the left atrium in utero because oxygenated blood is provided by the placenta). See illustration below.
 
 
6. Hypoplastic Left Heart Syndrome (HLHS)
The Hypoplastic Left Heart Syndrome is one of the most complex heart defects. Essentially, the left ventricle is so underdeveloped that it might as well be completely missing. Due to the complexity, other anomalies occur as well, including a small aorta, a small aortic arch, a large Patent Ductus Arteriosus (PDA), and an Atrial Septal Defect (ASD). All of these additional anomalies are a result of the cardiac mechanics attempting to regulate the hypoplastic left ventricle. See illustration below. 
 
 
In such severe defects, transplants may be utilized. However, due to the scarcity of newborn organs and the chance of transplant rejection, surgeries have been developed to correct this problem. The treatment for this defect is usually completed with three surgeries; the Norwood, the Glenn and the Fontan procedures done at 1 week, 3-6 months, and 2-3 years respectively. These surgeries essentially work with the defect and ultimately make a workable pumping mechanism and eventually use the right ventricle as the primary chamber for pumping blood to the body.
 
7. Interrupted Aortic Arch/Ventricular Septic Defect
This defect is almost always accompanied with a Ventricular Septal Defect (VSD), and refers to an absence or discontinuation of the descending aorta. The aorta is the major vessel that takes the blood from the left ventricle, carrying it to the rest of the body. When this vessel is interrupted, the body compensates by shunting blood from the left ventricle through a hole due to VSD into the right ventricle, then up through the Patent Ductus Arteriosus (PDA; a hole between the aorta and the pulmonary artery that should close at birth) into the descending aorta. See illustration below. 
 
 
8. Patent Ductus Arteriosus (PDA)
In utero, the child has a structure known as the Ductus Arteriosus. This structure shunts blood away from the lungs into the aorta.  The lungs are not used in utero because oxygen is supplied by the mother via the placenta, as the child does not yet breathe independently. At birth, with the first cry, this structure snaps shut and should be completely sealed within the first 24 hours of life. However, when this fails to happen, the connection remains open throughout one’s life and is called a PDA. See illustration below.  
 
PDA causes blood in the aorta, fully oxygenated and ready to provide the rest of the body with oxygen, to be shunted back down to the pulmonary artery, creating a highly ineffective pumping system. Blood saturated with oxygen being repeatedly cycled through the lungs by the pulmonary artery means that less blood is sent out to the body. The child often has an enlarged heart due to the high volume of blood traffic, as well as a high blood volume in the lungs.
 
9. Pulmonary Stenosis (PS)/ Pulmonary Valvular Stenosis (PVS)
This defect involves the pulmonary artery. The pulmonary valve separating the right atrium from the pulmonary artery should be flexible, to allow for smooth blood flow. However, in this defect, a stenosis (narrowing) has occurred at or around the pulmonary valve, consequently inhibiting the flow of blood to the lungs for oxygenation. See illustration below.
 
This narrowing can occur at the valve, or immediately after. If the narrowing is at the valve, the defect is called Pulmonary Valvular Stenosis (PVS); if the defect is in the vessel, then it is simply called Pulmonary Stenosis (PS). 
 
10. Pulmonary Atresia (PA)
Pulmonary Atresia is when the pulmonary valve fails to develop an opening, resulting in a blockage between the right ventricle and the pulmonary artery, preventing blood from getting to the lungs. Several complications accompany this defect, including a smaller right ventricle (as it is not in strenuous use) and both the Ductus Arteriosus and Foramen Ovale (remnants of the fetal circulatory system) remain patent (open) in order to bypass the pulmonary valve and provide a compensatory passage for blood flow.
Rather than following its intended course, the blood travels through the Patent Foramen Ovale (PFO) into the left atrium, from which the blood goes up the aorta with some of the blood going through the Patent Ductus Arteriosus (PDA) down to the lungs, while the rest of the blood continues to the body. See illustration below.
 
11. Single Ventricle Anomalies
Single Ventricle Anomalies is a term applied to several different defects; the name simply means that one of the two ventricles is underdeveloped to the point that it is unable to function adequately. Defects in this category are numerous, including disorders such as Tricuspid Atresia and Hypoplastic Left Heart Syndrome.
 
12. Tetralogy of Fallot
Tetralogy of Fallot is a complex heart defect involving a combination of four specific defects (tetra=four), including pulmonary stenosis, Ventricular Septal Defect (VSD), overriding aorta, and right ventricle hypertrophy. Pulmonary Stenosis is when there is a narrowing of the pulmonary artery, which decreases blood flow. Secondly, a VSD, the most common pediatric heart defect, is a hole between the right and left ventricles of the heart (discussed in detail on page 18). Thirdly, an overriding aorta simply means that the aorta (the vessel that carries blood from the heart to the body) appears to stem from both the right and the left ventricles instead of just the left, as in a normal heart. This causes a mixing of oxygenated and deoxygenated blood, and the child will often exhibit a cyanotic (blue) color. Lastly, right ventricular hypertrophy is when the right ventricle is overly muscular and large in size, compensating for an increased workload. Due to the complexity of the defect, the child can also exhibit additional defects, such as an ASD, poor placement of the coronary arteries, etc. Surgery is always needed to correct this problem.
 
 
13. Total Anomalous Pulmonary Venous Return (TAPVR)
This defect is a rare abnormality involving the placement of the pulmonary veins. Normally, the pulmonary veins take blood from the lungs and dump it into the left atrium to be sent out to the body. With this defect, however, the pulmonary veins drain back into the right atrium instead of the left. This means that all of the oxygenated blood returns to the right ventricle, mixing with the deoxygenated blood that has returned from the body, thus lowering the oxygen saturation of the blood. See illustration below.
 
 
In addition to the low oxygen saturation, the Foramen Ovale (a hole between the atria from the fetal circulatory system that should completely close within 24 hours of birth) remains open because of the pressure gradient caused by the TAPVR. The Foramen Ovale becomes an Atrial Septal Defect (ASD) that allows a way for the mixed blood from the right atria to travel to the left atria and ultimately to the left ventricle to at least partially oxygenate the rest of the body.
 
14. Transposition of the Great Arteries (TGA)
TGA is when the aorta and the pulmonary artery are switched; the pulmonary artery rises from the left ventricle and the aorta rises from the right ventricle, which is the opposite of what a normal heart should look like. This causes a massive problem as blood is going in the exact opposite area of the body where it is needed. See illustration below.
 
 
With this defect, the blood is trapped on either side of the heart; the blood on the right side mostly stays on the right side, cycling through the lungs and back to the right side, and the blood on the left side mostly stays on the left, cycling through the body and back to the left side. Consequently, the heart is not working in a functional manner and, ultimately, very little oxygenated blood escapes this ineffective cycle to nourish the body.
Like TAPVR, TGA also causes a structural defect to compensate for this anomaly. The first possibility is that the two fetal circulatory structures (the Foramen Ovale and the Ductus Arteriosus) may remain open in order to provide a passageway for blood to flow between the right and left sides of the heart. The second possibility is the presence of a Ventricle Septal Defect (VSD) or an Atrial Septal Defect (ASD). In either case, there is an abnormal structure allowing the passage of blood between the two sides of the heart. To correct this defect (or series of defects), major surgery is required.
 
15. Tricuspid Atresia
Tricuspid Atresia is where the tricuspid valve (the valve between the right atrium and the right ventricle) fails to develop normally. As a result, the right ventricle is seriously underdeveloped (qualifying this defect as a single ventricle anomaly, as discussed on page 12) and other structural abnormalities may be present as well, such as VSDs, ASDs, PDAs, and TGAs. See illustration below.
 
 
The implications of this defect are that a less than normal amount of blood goes to the lungs. Blood therefore, passes through the Foramen Ovale (a structure from fetal circulation), creating as ASD (Atrial Septal Defect) for the blood to pass over to the left side of the heart. Then either a VSD (Ventricular Septal Defect) or PDA (Patent Ductus Arteriosus) allows the passage of blood to the lungs. 
 
16. Truncus Arteriosus
Truncus Arteriosus is where a single artery emerging from the heart forms both the pulmonary artery and the aorta (in a normal heart these are two separate vessels). See illustration below. 
 
A Ventricular Septal Defect (VSD) is typically present as well. This second defect allows the mixed blood to pass through the single artery, and go to both the lungs and the body.
 
17. Vascular Rings
The term “Vascular Rings” applies to a number of defects, all of which involve a deformation of the aortic arch around the esophagus or the trachea. A variety of deformations can occur, but they all in some way restrict the trachea or esophagus. As you can imagine, such a defect not only affects the patient’s cardiovascular system, but the respiratory and gastrointestinal systems as well. In addition to signs of a cardiac defect, patients may also have symptoms of noisy breathing or difficulty swallowing.
 
18. Ventricular Septal Defect (VSD)
Ventricular Septal Defects are one of the most common pediatric cardiac defects. In normal cardiology, the right side of the heart receives deoxygenated blood from the body and takes the blood to the lungs to be re-oxygenated. The blood then goes to the left side of the heart where it is pumped out to the body. A VSD indicates that there is a hole between the right and left ventricles of the heart, causing the oxygenated and deoxygenated blood to mix. Because of different pressure gradients (the left side of the heart has a higher pressure than the right), blood is shunted from the left ventricle to the right. See illustration below. 
 
As a result, the heart becomes an ineffective pump, as oxygenated blood is sent to the lungs twice to be oxygenated. The size, location, and composition of the VSD dictate the severity.
 
19. Univentricular Heart
This is a very rare heart defect. The American Heart Association quotes its frequency as 54 cases per million, or .0054% of the population. 
The two ventricles of the heart are malformed into one super-ventricle, resulting in a dangerous and inefficient mixture of oxygenated and deoxygenated blood. Surgical correction usually requires two separate operations. The American Heart Association further says that the univentricular heart defect has "inspired some of the most creative surgical and interventional approaches in human history."
Glossary