Atrioventricular septal defect
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Atrioventricular septal defect (AVSD) or atrioventricular canal defect (AVCD), also known as "common atrioventricular canal" (CAVC) or "
endocardial cushion Endocardial cushions, or atrioventricular cushions, refer to a subset of cells in the development of the heart that play a vital role in the proper formation of the heart septa. They develop on the atrioventricular canal and conotruncal region of ...
defect" (ECD), is characterized by a deficiency of the
atrioventricular septum The atrioventricular septum is a septum of the heart between the right atrium (RA) and the left ventricle (LV). Although the name "atrioventricular septum" implies any septum between an atrium and a ventricle, in practice the divisions from RA to ...
of the
heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
that creates connections between all four of its chambers. It is caused by an abnormal or inadequate fusion of the superior and inferior
endocardial cushions Endocardial cushions, or atrioventricular cushions, refer to a subset of cells in the development of the heart that play a vital role in the proper formation of the heart septa. They develop on the atrioventricular canal and conotruncal region of ...
with the mid portion of the
atrial septum The interatrial septum is the wall of tissue that separates the right and left atria of the heart. Structure The interatrial septum is a that lies between the left atrium and right atrium of the human heart. The interatrial septum lies at angl ...
and the muscular portion of the
ventricular septum The interventricular septum (IVS, or ventricular septum, or during development septum inferius) is the stout wall separating the ventricles, the lower chambers of the heart, from one another. The ventricular septum is directed obliquely backwar ...
.


Symptoms and signs

Symptoms include difficulty breathing (
dyspnea Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing di ...
) and bluish discoloration on skin, fingernails, and lips (
cyanosis Cyanosis is the change of body tissue color to a bluish-purple hue as a result of having decreased amounts of oxygen bound to the hemoglobin in the red blood cells of the capillary bed. Body tissues that show cyanosis are usually in locations ...
). A newborn baby will show signs of heart failure such as edema, fatigue, wheezing, sweating and irregular heartbeat.


Complications

Normally, the four chambers of the heart divide oxygenated and de-oxygenated blood into separate pools. When holes form between the chambers, as in AVSD, the pools can mix. Consequently, arterial blood supplies become less oxygenated than normal, causing ischemia and cyanosis in distal tissues. To compensate, the heart must pump a larger volume of blood to deliver enough oxygen, leading to cardiac enlargement and
hypertrophy Hypertrophy is the increase in the volume of an organ or tissue due to the enlargement of its component cells. It is distinguished from hyperplasia, in which the cells remain approximately the same size but increase in number.Updated by Linda J. ...
. The development of pulmonary hypertension is very serious. And this because the
left ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the uppe ...
is weakened due to its overuse. When this happens, the pressure backs up into the
pulmonary veins The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart. The largest pulmonary veins are the four ''main pulmonary veins'', two from each lung that drain into the left atrium of the heart. The pulmonary vei ...
and the lungs. This type of damage is irreversible which is why immediate treatment is recommended after diagnosis.


Associated conditions

Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
is often associated with AVCD. Other risk factors include: having a parent with a
congenital heart defect A congenital heart defect (CHD), also known as a congenital heart anomaly and congenital heart disease, is a defect in the structure of the heart or great vessels that is present at birth. A congenital heart defect is classed as a cardiovascul ...
, alcohol use while pregnant, uncontrolled
diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
treatment during pregnancy and some medications during pregnancy. This type of congenital heart defect is associated with patients with
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
(trisomy 21) or heterotaxy syndromes. 45% of children with Down syndrome have congenital heart disease. Of these, 35–40% have AV septal defects. Approximately 40-50% of fetuses diagnosed with AVCD have Down syndrome, and a further 15-20% are associated with other
chromosomal abnormalities A chromosomal abnormality, chromosomal anomaly, chromosomal aberration, chromosomal mutation, or chromosomal disorder, is a missing, extra, or irregular portion of chromosomal DNA. These can occur in the form of numerical abnormalities, where the ...
and syndromes, such as
DiGeorge syndrome DiGeorge syndrome, also known as 22q11.2 deletion syndrome, is a syndrome caused by a microdeletion on the long arm of chromosome 22. While the symptoms can vary, they often include congenital heart problems, specific facial features, frequent i ...
. The remaining 30-40% of cases are not linked to a syndrome, with AVCD observed without other major defects. AVCD is also linked with
Noonan syndrome Noonan syndrome (NS) is a genetic disorder that may present with mildly unusual facial features, short height, congenital heart disease, bleeding problems, and skeletal malformations. Facial features include widely spaced eyes, light-colored ...
. The pattern seen in those patients with Noonan syndrome differ from those patients who have
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
in that "partial" AVCD is more prevalent in those with NS, whereas those with down syndrome show a prevalence of the "complete" form of AVCD.


Pathophysiology

Defective embryonic formation of the heart results in multiple holes between the
heart chambers The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide ...
. In AVSD, all four chambers are connected, but the exact characteristics of holes and malformations may vary between patients. Even within the categories of "complete" and "partial" AVSD, multiple morphologies exist, with varying clinical consequences. Clinical and physiological manifestations of disease may also change over time, in response to continued stress.


Genetic Relationship

Like other congenital heart defects, major associations have been found between AVCD and genes regulating embryonic cell cilia. These human cell cilia normally contain receptors for signal molecules that regulate the healthy and organized tissue. Dysfunctional cilia can create multiple disease manifestations, leading to broad syndromes. Chromosome 21 harbors important regulators for cilia, and trisomy 21 (Down syndrome) can de-regulate them.


Diagnosis

AVSDs can be detected by
cardiac auscultation Heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. Specifically, the sounds reflect the turbulence created when the heart valves snap shut. In cardiac auscultation, an examiner may use a stet ...
; they cause atypical murmurs and loud heart tones. Confirmation of findings from cardiac auscultation can be obtained with a cardiac
ultrasound Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...
( echocardiography - less invasive) and cardiac catheterization (more invasive). It is also possible to diagnose AVSD in-utero via routine fetal ultrasounds or, more conclusively, fetal echocardiograms.


Classification

A variety of different classifications have been used, but the defects are usefully divided into "partial" and "complete" forms. * In the partial AVSD, there is a small or partial defect in the interventricular septum, and a primum
atrial septal defect Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this d ...
, which is a moderate or large connection between the atria, often featuring
mitral valve regurgitation Mitral regurgitation (MR), also known as mitral insufficiency or mitral incompetence, is a form of valvular heart disease in which the mitral valve is insufficient and does not close properly when the heart pumps out blood. Section: Valvular Hea ...
. Partial AVSD may be asymptomatic in early childhood, but typically progresses by late childhood or adulthood into symptoms of heart failure. The onset of symptoms may be earlier in children with more significant mitral regurgitation. * In the complete AVSD (CAVSD), there is a large ventricular component beneath either or both the superior or inferior bridging leaflets of the AV valve. The defect involves the whole area of the junction of the upper and lower chambers of the heart, i.e. where the atria join the ventricles. There is a large hole between the lower portion of the atria and the upper or 'inlet' portion of the ventricles and this is associated with a significant abnormality of the valves separating the atria from the ventricles. The valves in effect become a common atrio-ventricular valve, and the severity of the defect depends largely on the supporting attachments of the valve to the ventricles and whether the valve allows dominant flow from the right atrium to right ventricle and from left atrium to left ventricle ("unbalanced" flow). The overall problems are similar to those of VSD but are more complicated. There is an increased flow of blood to the lungs through both the ventricular and atrial components of the defect. In addition, the abnormal atrio-ventricular valve invariably leaks, so that when the ventricles contract, blood flows not only forwards to the body and the lungs, but also backwards into the atria. The back-pressure effect on the atria causes congestion of blood in the left atrium in particular, and this in turn causes congestion in the veins draining the lungs. The effect on the baby is to worsen the heart failure that is associated with an isolated VSD and to hasten the onset of pulmonary hypertension. It should be mentioned that CAVSD is found in approximately one-third of babies who have
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
, but it also occurs as an isolated abnormality.


Treatment

Treatment is surgical and involves closure of the atrial and ventricular septal defects and restoration of a competent left AV valve as far as is possible. Open surgical procedures require a
heart-lung machine Cardiopulmonary bypass (CPB) is a technique in which a machine temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and oxygen to the body. The CPB pump itself is often referred to as a ...
and are done with a
median sternotomy Median sternotomy is a type of surgical procedure in which a vertical inline incision is made along the sternum, after which the sternum itself is divided using a sternal saw. This procedure provides access to the heart and lungs for surgical pro ...
. Surgical mortality for uncomplicated ostium primum defects in experienced centers is 2%; for uncomplicated cases of complete atrioventricular canal defect, 4% or less. Certain complications such as
tetralogy of Fallot Tetralogy of Fallot (TOF), formerly known as Steno-Fallot tetralogy, is a congenital heart defect characterized by four specific cardiac defects. Classically, the four defects are: *pulmonary stenosis, which is narrowing of the exit from the r ...
or highly unbalanced flow across the common AV valve can increase risk significantly. Infants born with AVSD are generally in sufficient health to not require immediate corrective surgery. If surgery is not required immediately after birth, the newborn will be closely monitored for the next several months, and the operation held-off until the first signs of lung distress or heart failure. This gives the infant time to grow, increasing the size of, and thereby the ease of operation on, the heart, as well as the ease of recovery. Infants will generally require surgery within three to six months, however, they may be able to go up to two years before the operation becomes necessary, depending on the severity of the defect.


See also

*
Atrial septal defect Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this d ...
*
Congenital heart disease A congenital heart defect (CHD), also known as a congenital heart anomaly and congenital heart disease, is a defect in the structure of the heart or great vessels that is present at birth. A congenital heart defect is classed as a cardiovascular ...
*
Down syndrome Down syndrome or Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is usually associated with physical growth delays, mild to moderate intellectual dis ...
*
Heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
* Heart sounds * Pulmonary hypertension *
Ventricular septal defect A ventricular septal defect (VSD) is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart. The extent of the opening may vary from pin size to complete absence of the ventricular septum, creating one ...


References


External links

{{Medicine Congenital heart defects