Atrial septal defect (
ASD) is a form of congenital heart defect that enables blood flow between the left and right atria via the
interatrial septumThe interatrial septum is the wall of tissue that separates the right and left atria of the heart.-Development:The interatrial septum forms during the first and second months of fetal development. Formation of the septum occurs in several stages...
. The interatrial septum is the tissue that divides the
rightThe right atrium is one of four chambers in the human heart. It receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus, and pumps it into the right ventricle through the tricuspid valve...
and
leftThe left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the atrioventricular valve.-Foramen ovale:...
atria. Without this septum, or if there is a defect in this septum, it is possible for blood to travel from the left side of the heart to the right side of the heart, or vice versa. Irrespective of interatrial communication bi-directions, this results in the mixing of arterial and venous blood. The mixing of arterial and venous blood may or may not be hemodynamically significant, if even clinically significant. This mixture of blood may or may not result in what is known as a "shunt". The amount of shunting present, if any, dictates hemodynamic significance (see Pathophysiology below). A "right-to-left-shunt" typically poses the more dangerous scenario (see Pathophysiology below).
The right side of the heart contains
venousIn the circulatory system, veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood...
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
with a low
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
content, and the left side of the heart contains
arterialArteries are blood vessels that carry blood away from the heart. All arteries, with the exception of the pulmonary and umbilical arteries, carry oxygenated blood.The circulatory system is extremely important for sustaining life...
bloodBlood is a specialized bodily fluid that delivers necessary substances to the body's cells — such as nutrients and oxygen — and transports waste products away from those same cells....
with a high
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
content. The construction of a heart void of an ASD prevents interatrial communication by means of an uncompromised interatrial septum. This prevents the atria from regular communication with each other, and thus oxygen-rich blood and oxygen-deficient blood do not mix together improperly.
During development of the
fetusA fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth. The plural is fetuses....
, the interatrial septum develops to eventually separate the
leftThe left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the atrioventricular valve.-Foramen ovale:...
and
rightThe right atrium is one of four chambers in the human heart. It receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus, and pumps it into the right ventricle through the tricuspid valve...
atria. The
foramen ovaleIn the fetal heart, the foramen ovale allows blood to enter the left atrium from the right atrium. It is one of two shunts, the other being the ductus arteriosus, that allows blood that still escapes to the right ventricle to bypass the pulmonary circulation. Another similar adaptation in the...
remains open during fetal development to allow blood from the venous system to bypass the lungs directly and enter the circulatory system. This is because the oxygen content of the fetal arterial system is provided by the
placentaThe placenta is an organ unique to mammals that connects the developing fetus to the uterine wall. The placenta supplies the fetus with oxygen and food, and allows fetal waste to be disposed of via the maternal kidneys...
, as the lungs of the fetus are nonfunctional when it comes to oxygenizing the blood. A layer of tissue begins to cover the foramen ovale during fetal development, in which typically, after birth, the pressure in the pulmonary circulatory system drops, thus causing the foramen ovale to close entirely. In approximately 25% of adults, the foramen ovale does not entirely seal. In this case, elevation of pressure in the pulmonary circulatory system (ie:
pulmonary hypertensionIn medicine, pulmonary hypertension is an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion...
due to various causes, or transiently during a
coughA cough , in medicine, is a sudden and often repetitively occurring defense reflex which helps to clear the large breathing passages from excess secretions, irritants, foreign particles and microbes...
) can cause the foramen ovale to remain open. This is known as a
patent foramen ovale (
PFO).
Pathophysiology
In unaffected individuals, the chambers of the left side of the heart make up a higher pressure system than the chambers of the right side of the heart. This is because the
left ventricleThe left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...
has to produce enough pressure to pump blood throughout the entire body, while the
right ventricleThe right ventricle is one of four chambers in the human heart. It receives deoxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk....
only has to produce enough pressure to pump blood to the
lungThe lung or pulmonary system is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart...
s.
In the case of a large ASD (>9mm), which may result in a clinically remarkable
left-to-right shuntCardiac shunts may be described as right-left, left-to-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic. The direction may be controlled by left and/or right heart pressure, a biological or artificial heart valve or both...
, blood will shunt from the
left atriumThe left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the atrioventricular valve.-Foramen ovale:...
to the
right atriumThe right atrium is one of four chambers in the human heart. It receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus, and pumps it into the right ventricle through the tricuspid valve...
causing excessive interatrial communication (In the case of hemodynamically significant ASD (Qp:Qs > 1.5:1), the patient is often found to be notably symptomatic and ASD repair may be indicated). This extra blood from the left atrium may cause a volume overload of both the
right atriumThe right atrium is one of four chambers in the human heart. It receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus, and pumps it into the right ventricle through the tricuspid valve...
and the
right ventricleThe right ventricle is one of four chambers in the human heart. It receives deoxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk....
, which if left untreated, can result in enlargement of the right side of the heart and ultimately heart failure.
Any process that increases the pressure in the
left ventricleThe left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...
can cause worsening of the left-to-right shunt. This includes
hypertensionHypertension is a chronic medical condition in which the blood pressure is elevated. It is also referred to as high blood pressure or shortened to HT, HTN or HPN. The word "hypertension", by itself, normally refers to systemic, arterial hypertension.Hypertension can be classified as either...
, which increases the pressure that the left ventricle has to generate in order to open the
aortic valveThe aortic valve is one of the valves of the heart. It lies between the left ventricle and the aorta.-Function and physiology:During ventricular systole, pressure rises in the left ventricle. When the pressure in the left ventricle rises above the pressure in the aorta, the aortic valve opens,...
during ventricular
systoleSystole may refer to:*Systole , a term used to describe entry into the imagination in a text*Systole , a term describing the contraction of the heart*Systolic array, a term used in computer architecture...
, and coronary artery disease which increases the stiffness of the left ventricle, thereby increasing the filling pressure of the left ventricle during ventricular
diastoleDiastole is the period of time when the heart fills with blood after systole . Ballistics accurately describes Diastole as recoil opposed to coil or Systole. Ventricular diastole is the period during which the ventricles are relaxing, while atrial diastole is the period during which the atria are...
.
The right ventricle will have to push out more blood than the left ventricle due to the left-to-right shunt. This constant overload of the right side of the heart will cause an overload of the entire pulmonary vasculature. Eventually the pulmonary vasculature will develop
pulmonary hypertensionIn medicine, pulmonary hypertension is an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion...
to try to divert the extra blood volume away from the lungs.
The pulmonary hypertension will cause the right ventricle to face increased
afterloadIn cardiac physiology, afterload is used to mean the tension produced by a chamber of the heart in order to contract. If the chamber is not mentioned, it is usually assumed to be the left ventricle. However, the strict definition of the term relates to the properties of a single cardiac myocyte...
in addition to the increased preload that the shunted blood from the left atrium to the right atrium caused. The right ventricle will be forced to generate higher pressures to try to overcome the pulmonary hypertension. This may lead to right ventricular failure (dilatation and decreased
systolicSystole may refer to:*Systole , a term used to describe entry into the imagination in a text*Systole , a term describing the contraction of the heart*Systolic array, a term used in computer architecture...
function of the right ventricle) or elevations of the right sided pressures to levels greater than the left sided pressures.
When the pressure in the right atrium rises to the level in the left atrium, there will no longer be a pressure gradient between these heart chambers, and the left-to-right shunt will diminish or cease.
If left uncorrected, the pressure in the right side of the heart will be greater than the left side of the heart. This will cause the pressure in the right atrium to be higher than the pressure in the left atrium. This will reverse the pressure gradient across the ASD, and the shunt will reverse; a
right-to-left shunt will exist. This phenomenon is known as
Eisenmenger's syndromeEisenmenger's syndrome is defined as the process in which a left-to-right shunt caused by a ventricular septal defect in the heart causes increased flow through the pulmonary vasculature, causing pulmonary hypertension, which in turn, causes increased pressures in the right side of the heart and...
.
Once right-to-left shunting occurs, a portion of the oxygen-poor blood will get shunted to the left side of the heart and ejected to the peripheral vascular system. This will cause signs of
cyanosisCyanosis is a blue coloration of the skin and mucous membranes due to the presence of > 5g/dl deoxygenated hemoglobin in blood vessels near the skin surface....
.
Epidemiology
As a group, atrial septal defects are detected in 1 child per 1500 live births. PFO are quite common (appearing in 10 - 20% of adults) but asymptomatic and therefore undiagnosed. ASDs make up 30 to 40% of all congenital heart disease that is seen in adults.
The ostium secundum atrial septal defect accounts for 7% of all congenital heart lesions. This lesion shows a female preponderance, with a male : female ratio of 1:2.
Types of atrial septal defects
There are many types of atrial septal defects. They are differentiated from each other by whether they involve other structures of the heart and how they are formed during the developmental process during early
fetalA fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth. The plural is fetuses....
development.
Ostium secundum atrial septal defect
The
ostium secundum atrial septal defect is the most common type of atrial septal defect, and comprises 6-10% of all congenital heart diseases.
The secundum atrial septal defect usually arises from an enlarged foramen ovale, inadequate growth of the septum secundum, or excessive absorption of the septum primum. Ten to twenty percent of individuals with ostium secundum ASDs also have
mitral valve prolapseMitral valve prolapse is a valvular heart disease characterized by the displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole. There are various types of MVP, broadly classified as classic and nonclassic. In its nonclassic form, MVP carries a low risk of...
.
Natural history
Most individuals with an uncorrected secundum ASD don't have significant symptoms through early adulthood. About 70% develop symptoms by the time they are in their 40s. Symptoms are typically decreased exercise tolerance, easy fatigueability,
palpitationA palpitation is an abnormal awareness of the beating of the heart, whether it is too slow, too fast, irregular, or at its normal frequency. It can be caused by ectopic beat, which is a more specific diagnosis....
s, and syncope.
Complications of an uncorrected secundum ASD include
pulmonary hypertensionIn medicine, pulmonary hypertension is an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion...
, right-sided
heart failureHeart failure is a condition in which a problem with the structure or function of the heart impairs its ability to supply sufficient blood flow to meet the body's needs...
,
atrial fibrillationAtrial fibrillation is the most common cardiac arrhythmia and involves the two upper chambers of the heart. Its name comes from the fibrillating of the heart muscles of the atria, instead of a coordinated contraction...
or
flutterAtrial flutter is an abnormal heart rhythm that occurs in the atria of the heart. When it first occurs, it is usually associated with a fast heart rate or tachycardia , and falls into the category of supra-ventricular tachycardias...
, stroke, and
Eisenmenger's syndromeEisenmenger's syndrome is defined as the process in which a left-to-right shunt caused by a ventricular septal defect in the heart causes increased flow through the pulmonary vasculature, causing pulmonary hypertension, which in turn, causes increased pressures in the right side of the heart and...
.
While pulmonary hypertension is unusual before 20 years of age, it is seen in 50% of individuals above the age of 40. Progression to
Eisenmenger's syndromeEisenmenger's syndrome is defined as the process in which a left-to-right shunt caused by a ventricular septal defect in the heart causes increased flow through the pulmonary vasculature, causing pulmonary hypertension, which in turn, causes increased pressures in the right side of the heart and...
occurs in 5 to 10% of individuals late in the disease process.
Patent foramen ovale
A
patent foramen ovale (
PFO) is a small channel that has little hemodynamic consequence; it is a remnant of the fetal
foramen ovaleIn the fetal heart, the foramen ovale allows blood to enter the left atrium from the right atrium. It is one of two shunts, the other being the ductus arteriosus, that allows blood that still escapes to the right ventricle to bypass the pulmonary circulation. Another similar adaptation in the...
. Clinically it is linked to
decompression sicknessDecompression sickness describes a condition arising from the precipitation of dissolved gasses into bubbles inside the body on depressurisation...
, paradoxical embolism and
migraineMigraine is a neurological syndrome characterized by altered bodily perceptions, severe headaches, and nausea. Physiologically, the migraine headache is a neurological condition more common to women than to men. The word migraine was borrowed from Old French migraigne...
. On echocardiography, there may not be any shunting of blood noted except when the patient coughs.
There is debate within the neurology and cardiology communities about the role of a PFO in cryptogenic (i.e. of unknown cause) neurologic events such as strokes and transient ischemia attacks (TIAs) without any other potential cause. Even though some data suggested that PFOs may be involved in the pathogenesis of some migraine headaches, this hypothesis has been disproved. Several clinical trials are currently underway to investigate the role of PFO in these clinical situations.
Ostium primum atrial septal defect
A defect in the
ostium primumIn the developing heart, for a time the atria communicate with each other by an opening between the free edge of the septum primum and the AV cushions, known as the ostium primum , below the free margin of the septum....
is occasionally classified as an atrial septal defect, but it is more commonly classified as an
atrioventricular septal defectAtrioventricular septal defect or atrioventricular canal defect , previously known as "common atrioventricular canal" or "endocardial cushion defect", is characterized by a deficiency of the atrioventricular septum of the heart...
.
Sinus venosus atrial septal defect
A sinus venosus ASD is a type of atrial septum defect in which the defect in the septum involves the venous inflow of either the
superior vena cavaThe superior vena cava is a large diameter, yet short vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium....
or the
inferior vena cavaThe inferior vena cava is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....
.
A sinus venosus ASD that involves the superior vena cava makes up 2 to 3% of all interatrial communication. It is located at the junction of the superior vena cava and the right atrium. It is frequently associated with anomalous drainage of the right-sided
pulmonary veinA pulmonary vein is a large blood vessel of the human circulatory system that carries blood from the lungs to the left atrium of the heart. There are four pulmonary veins, two from each lung. They carry oxygenated blood, which is unusual since almost all other veins carry deoxygenated...
s into the right atrium (instead of the normal drainage of the pulmonary veins into the left atrium).
Common or single atrium
Common (or single) atrium is a failure of development of the embryologic components that contribute to the atrial septal complex. It is frequently associated with heterotaxy syndrome.
Diagnosis in children
Most individuals with a significant ASD are diagnosed
in uteroIn utero is a Latin term literally meaning "in the uterus". It is used in biology to describe the state of an embryo or fetus.-See also:* ex vivo* in silico* in situ* in vitro* in vivo...
or in early childhood with the use of ultrasonography or
auscultationAuscultation is the technical term for listening to the internal sounds of the body, usually using a stethoscope; based on the Latin verb auscultare "to listen"...
of the
heart soundsThe heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. This is also called a heartbeat...
during
physical examinationPhysical examination or clinical examination is the process by which a doctor investigates the body of a patient for signs of disease. It generally follows the taking of the medical history — an account of the symptoms as experienced by the patient...
.
Diagnosis in adults
Some individuals with an ASD will have undergone surgical correction of their ASD during childhood. The development of signs and symptoms due to an ASD are related to the size of the intracardiac shunt. Individuals with a larger shunt tend to present with symptoms at a younger age.
Adults with an uncorrected ASD will present with symptoms of dyspnea on exertion (shortness of breath with minimal exercise),
congestive heart failureHeart failure is a condition in which a problem with the structure or function of the heart impairs its ability to supply sufficient blood flow to meet the body's needs...
, or cerebrovascular accident (stroke). They may be noted on routine testing to have an abnormal
chest x-rayIn medicine, a chest radiograph, commonly called a chest x-ray , is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures...
or an abnormal EKG and may have
atrial fibrillationAtrial fibrillation is the most common cardiac arrhythmia and involves the two upper chambers of the heart. Its name comes from the fibrillating of the heart muscles of the atria, instead of a coordinated contraction...
.
Physical exam auscultationAuscultation is the technical term for listening to the internal sounds of the body, usually using a stethoscope; based on the Latin verb auscultare "to listen"...
of the heart
The physical findings in an adult with an ASD include those related directly to the intracardiac shunt, and those that are secondary to the
right heart failureHeart failure is a condition in which a problem with the structure or function of the heart impairs its ability to supply sufficient blood flow to meet the body's needs...
that may be present in these individuals.
Upon
auscultationAuscultation is the technical term for listening to the internal sounds of the body, usually using a stethoscope; based on the Latin verb auscultare "to listen"...
of the
heart soundsThe heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. This is also called a heartbeat...
, there may be an
ejection systolic murmur that is attributed to the pulmonic valve. This is due to the increased flow of blood through the pulmonic valve rather than any structural abnormality of the valve leaflets.
In unaffected individuals, there are respiratory variations in the
splitting of the second heart soundA split S2 is a finding upon auscultation of the S2 heart sound.It is caused when the closure of the aortic valve and the closure of the pulmonary valve are not synchronized.-Physiologic split:...
(S
2). During respiratory inspiration, the negative intrathoracic pressure causes increased blood return into the right side of the heart. The increased blood volume in the right ventricle causes the pulmonic valve to stay open longer during ventricular
systoleSystole may refer to:*Systole , a term used to describe entry into the imagination in a text*Systole , a term describing the contraction of the heart*Systolic array, a term used in computer architecture...
. This causes a normal delay in the P
2 component of S
2. During expiration, the positive intrathoracic pressure causes decreased blood return to the right side of the heart. The reduced volume in the right ventricle allows the pulmonic valve to close earlier at the end of ventricular systole, causing P
2 to occur earlier.
In individuals with an ASD, there is a
fixed splitting of S2. The reason why there is a fixed splitting of the second heart sound is that the extra blood return during inspiration gets equalized between the left and right atrium due to the communication that exists between the atria in individuals with ASD.
The right ventricle can be thought of as continuously overloaded because of the left to right shunt, producing a widely split S2. Because the atria are linked via the atrial septal defect, inspiration produces no net pressure change between them, and has no effect on the splitting of S2. Thus, S2 is split to the same degree during inspiration as expiration, and is said to be “fixed.”
Echocardiography
In transthoracic
echocardiographyAn echocardiogram, often referred to in the medical community as a cardiac ECHO or simply an ECHO, is a sonogram of the heart. Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart...
, an atrial septal defect may be seen on color flow imaging as a jet of blood from the left atrium to the right atrium.
If agitated saline is injected into a peripheral
veinIn the circulatory system, veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood...
during echocardiography, small air bubbles can be seen on echocardiographic imaging. It may be possible to see bubbles travel across an ASD either at rest or during a cough. (Bubbles will only flow from right atrium to left atrium if the RA pressure is greater than LA).
Because better visualization of the atria is achieved with transesophageal echocardiography, this test may be performed in individuals with a suspected ASD which is not visualized on transthoracic imaging.
Newer techniques to visualize these defects involve intracardiac imaging with special catheters that are typically placed in the venous system and advanced to the level of the heart. This type of imaging is becoming more common and involves only mild sedation for the patient typically.
If the individual has adequate echocardiographic windows, it is possible to use the echocardiogram to measure the cardiac output of the left ventricle and the right ventricle independently. In this way, it is possible to estimate the shunt fraction using echocardiograpy.
Transcranial Doppler (TCD) Bubble study
A less invasive method for detecting a PFO or other ASDs than transesophagal ultrasound is Transcranial Doppler with bubble contrast. This method reveals the cerebral impact of the ASD or PFO.
Electrocardiogram
The ECG findings in atrial septal defect vary with the type of defect the individual has. Individuals with atrial septal defects may have a prolonged PR interval (a
first degree heart blockFirst-degree AV block, or PR prolongation, is a disease of the electrical conduction system of the heart in which the PR interval is lengthened beyond 0.20 seconds....
). The prolongation of the PR interval is probably due to the enlargement of the atria that is common in ASDs and the increased distance due to the defect itself. Both of these can cause an increased distance of internodal conduction from the SA node to the AV node.
In addition to the PR prolongation, individuals with a primum ASD have a left axis deviation of the QRS complex while those with a secundum ASD have a right axis deviation of the QRS complex. Individuals with a sinus venosus ASD exhibit a left axis deviation of the P wave (not the QRS complex).
A common finding in the ECG is the presence of incomplete RBBB. In fact this finding is so characteristic that if it is absent, the diagnosis of ASD should be revised.
Treatment
Once someone is found to have an atrial septal defect, a determination of whether it should be corrected has to be made.
Surgical mortality due to closure of an ASD is lowest when the procedure is performed prior to the development of significant pulmonary hypertension. The lowest mortality rates are achieved in individuals with a pulmonary artery systolic pressure of less than 40 mmHg.
If
Eisenmenger's syndromeEisenmenger's syndrome is defined as the process in which a left-to-right shunt caused by a ventricular septal defect in the heart causes increased flow through the pulmonary vasculature, causing pulmonary hypertension, which in turn, causes increased pressures in the right side of the heart and...
has occurred, there is significant risk of mortality regardless of the method of closure of the ASD. In individuals who have developed Eisenmenger's syndrome, the pressure in the right ventricle has raised high enough to reverse the shunt in the atria. If the ASD is then closed, the
afterloadIn cardiac physiology, afterload is used to mean the tension produced by a chamber of the heart in order to contract. If the chamber is not mentioned, it is usually assumed to be the left ventricle. However, the strict definition of the term relates to the properties of a single cardiac myocyte...
that the right ventricle has to act against has suddenly increased. This may cause immediate right ventricular failure, since it may not be able to pump the blood against the pulmonary hypertension.
Closure of an ASD in individuals under age 25 has been shown to have a low risk of complications, and individuals have a normal lifespan (comparable to a healthy age-matched population). Closure of an ASD in individuals between the ages of 25 and 40 who are asymptomatic but have a clinically significant shunt is controversial. Those that perform the procedure believe that they are preventing long-term deterioration in cardiac function and preventing the progression of pulmonary hypertension.
Methods of closure of an ASD include surgical closure and percutaneous closure.
Evaluation prior to correction
Prior to correction of an ASD, an evaluation is made of the severity of the individual's pulmonary hypertension (If present at all) and whether it is reversible (Closure of an ASD may be recommended for prevention purposes, to avoid such a complication in the first place. Pulmomary hypertension is not always present in adults that are diagnosed with an ASD in adulthood).
If pulmonary hypertension is present, the evaluation may include a right heart catheterization. This involves placing a catheter in the venous system of the heart and measuring pressures and oxygen saturations in the
SVCThe superior vena cava is a large diameter, yet short vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium....
,
IVCThe inferior vena cava is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....
,
right atriumThe right atrium is one of four chambers in the human heart. It receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus, and pumps it into the right ventricle through the tricuspid valve...
,
right ventricleThe right ventricle is one of four chambers in the human heart. It receives deoxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk....
,
pulmonary arteryThe pulmonary arteries carry blood from heart to the lungs. They are the only arteries that carry deoxygenated blood....
, and in the wedge position. Individuals with a pulmonary vascular resistance (PVR) of less than 7 wood units show regression of symptoms (including
NYHA functional classThe New York Heart Association Functional Classification provides a simple way of classifying the extent of heart failure. It places patients in one of four categories based on how much they are limited during physical activity; the limitations/symptoms are in regards to normal breathing and...
). On the other hand, individuals with a PVR of greater than 15 wood units have increased mortality associated with closure of the ASD.
If the pulmonary arterial pressure is more than 2/3 the systemic systolic pressure, there should be a net left-to-right shunt of at least 1.5:1 or evidence of reversibility of the shunt when given pulmonary artery vasodilators prior to surgery. (If eisenmenger's physiology has set in, it must be proven that the right-to-left shunt is reversible with pulmonary artery vasodilators prior to surgery.)
Surgical ASD closure
Surgical closure of an ASD involves opening up at least one
atriumIn anatomy, the atrium , sometimes called auricle, refers to a chamber or space. It may be the atrium of the lateral ventricle in the brain or the blood collection chamber of a heart. It has a thin-walled structure that allows blood to return to the heart. There is at least one atrium in animals...
and closing the defect with a patch under direct visualization.
Percutaneous ASD closure
Percutaneous closure of an ASD is currently only indicated for the closure of secundum ASDs with a sufficient rim of tissue around the septal defect so that the closure device does not impinge upon the
SVCThe superior vena cava is a large diameter, yet short vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium....
,
IVCThe inferior vena cava is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....
, or the
tricuspidThe tricuspid valve is on the right side of the heart, between the right atrium and the right ventricle. The normal tricuspid valve usually has three leaflets and three papillary muscles. They are connected to the papillary muscles by the chordae tendineae, which lie in the right ventricle...
or
mitralThe mitral valve is a dual-flap valve in the heart that lies between the left atrium and the left ventricle...
valves. The
AmplatzerDr. Kurt Amplatz is a retired radiologist and medical device inventor. He may be best known for the invention of the Amplatzer Septal Occluder, a device which repairs atrial septal defects of the heart by percutaneous catheter placement, avoiding open heart surgery. He also performed one of the...
Septal Occluder (ASO) is commonly used to close ASDs. The ASO consists of two self-expandable round discs connected to each other with a 4 mm waist, made up of 0.004–0.005´´ nitinol wire mesh filled with Dacron fabric. Implantation of the device is relatively easy. The prevalence of residual defect is low. The disadvantages are a thick profile of the device and concern related to a large amount of nitinol (a nickel-titanium compound) in the device and consequent potential for nickel toxicity.
Percutaneous closure is the method of choice in most centres.
Associated conditions
Due to the communication between the atria that occurs in ASDs, disease entities or complications from the condition, are possible.
Decompression sickness
ASDs, and particularly PFOs, are a predisposing risk factor for
decompression sicknessDecompression sickness describes a condition arising from the precipitation of dissolved gasses into bubbles inside the body on depressurisation...
in divers because a proportion of venous blood carrying inert gases, such as
heliumHelium is the chemical element with atomic number 2, and is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table...
or
nitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere.Many industrially important...
does not pass through the lungs.
The only way to release the excess inert gases from the body is to pass the blood carrying the inert gases through the
lungThe lung or pulmonary system is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart...
s to be exhaled. If some of the inert gas-laden blood passes through the PFO, it avoids the lungs and the inert gas is more likely to form large bubbles in the arterial blood stream causing
decompression sickness.
Paradoxical emboli
Venous
thrombiA thrombus , or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system...
(clots in the
veinIn the circulatory system, veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood...
s) are quite common. Embolization (dislodgement of thrombi) normally go to the lung and cause
pulmonary emboliPulmonary embolism is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream . Usually this is due to embolism of a thrombus from the deep veins in the legs, a process termed venous thromboembolism...
. In an individual with ASD, these emboli can potentially enter the arterial system. This can cause any phenomenon that is attributed to acute loss of blood to a portion of the body, including cerebrovascular accident (stroke), infarction of the
spleenThe spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells, holds a reserve in case of hemorrhagic shock, especially in...
or
intestineIn anatomy, the intestine is the segment of the alimentary canal extending from the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s, or even a distal extremity (i.e.: finger or toe).
This is known as a
paradoxical embolus because the clot material paradoxially enters the arterial system instead of going to the lungs.
Migraine
Some recent research has suggested that a proportion of cases of
migraineMigraine is a neurological syndrome characterized by altered bodily perceptions, severe headaches, and nausea. Physiologically, the migraine headache is a neurological condition more common to women than to men. The word migraine was borrowed from Old French migraigne...
may be caused by patent foramen ovale. While the exact mechanism remains unclear, closure of a PFO can reduce symptoms in certain cases. This remains controversial. 20% of the general population have a PFO, which for the most part, is asymptomatic. 20% of the female population have migraines. And, the
placebo effectPlacebo effect may refer to:* Placebo effect, the tendency of any medication or treatment, even an inert or ineffective one, to exhibit results simply because the recipient believes that it will work...
in migraine typically averages around 40%. The high frequency of these facts makes statistically significant relationships between PFO and migraine difficult (i.e., the relationship may just be chance or coincidence). In a large randomized controlled trial the higher prevalence of patent foramen ovale in migraine patients was confirmed, but migraine headache cessation was not more prevalent in the group of migraine patients that underwent closure of their patent foramen ovale.
See also
- Atrioventricular septal defect
Atrioventricular septal defect or atrioventricular canal defect , previously known as "common atrioventricular canal" or "endocardial cushion defect", is characterized by a deficiency of the atrioventricular septum of the heart...
- Cardiac output
Cardiac output is the volume of blood being pumped by the heart, in particular by a ventricle in a minute. This is measured in dm3 min-1...
- Congenital heart disease
- Heart sounds
The heart sounds are the noises generated by the beating heart and the resultant flow of blood through it. This is also called a heartbeat...
- Pulmonary hypertension
In medicine, pulmonary hypertension is an increase in blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, and other symptoms, all of which are exacerbated by exertion...
- Vascular resistance
Vascular resistance is a term used to define the resistance to flow that must be overcome to push blood through the circulatory system. The resistance offered by the peripheral circulation is known as the systemic vascular resistance , while the resistance offered by the vasculature of the lungs...
- Pulmonary vascular resistance
- Ventricular septal defect
A ventricular septal defect is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart.The ventricular septum consists of an inferior muscular and superior membranous portion and is extensively innervated with conducting cardiomyocytes...
- Illnesses of Ariel Sharon