Atrial Septal Defect
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Atrial septal defect (ASD) is 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 cardiovascular ...
in which blood flows between the atria (upper chambers) 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 ...
. Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO). It is common in patients with a congenital atrial septal
aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus (s ...
(ASA). After PFO closure the atria normally are separated by a dividing wall, the
interatrial 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 ...
. If this septum is defective or absent, then
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
-rich blood can flow directly from the left side of the heart to mix with the oxygen-poor blood in the right side of the heart; or the opposite, depending on whether the left or right atrium has the higher blood pressure. In the absence of other heart defects, the left atrium has the higher pressure. This can lead to lower-than-normal oxygen levels in the arterial blood that supplies the brain, organs, and tissues. However, an ASD may not produce noticeable signs or symptoms, especially if the defect is small. Also, in terms of health risks, people who have had a cryptogenic
stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
are more likely to have a PFO than the general population. A cardiac shunt is the presence of a net flow of blood through a defect, either from left to right or right to left. The amount of shunting present, if any, determines the hemodynamic significance of the ASD. A right-to-left-shunt results in venous blood entering the left side of the heart and into the arterial circulation without passing through the
pulmonary circulation The pulmonary circulation is a division of the circulatory system in all vertebrates. The circuit begins with deoxygenated blood returned from the body to the right atrium of the heart where it is pumped out from the right ventricle to the lungs ...
to be
oxygenate Oxygenated chemical compounds contain oxygen as a part of their chemical structure. The term usually refers to oxygenated chemical compounds added to fuels. Oxygenates are usually employed as gasoline additives to reduce carbon monoxide and soot ...
d. This may result in the clinical finding of
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 ...
, the presence of bluish-colored skin, especially of the lips and under the nails. During development of the baby, the interatrial septum develops to separate the left and right atria. However, a hole in the septum called the foramen ovale allows blood from the right atrium to enter the left atrium during fetal development. This opening allows blood to bypass the nonfunctional fetal lungs while the fetus obtains its oxygen from the
placenta The placenta is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate mater ...
. A layer of tissue called the septum primum acts as a valve over the foramen ovale during fetal development. After birth, the pressure in the right side of the heart drops as the lungs open and begin working, causing the foramen ovale to close entirely. In about 25% of adults, the foramen ovale does not entirely seal. In these cases, any elevation of the pressure in the pulmonary circulatory system (due to pulmonary hypertension, temporarily while
cough A cough is a sudden expulsion of air through the large breathing passages that can help clear them of fluids, irritants, foreign particles and microbes. As a protective reflex, coughing can be repetitive with the cough reflex following three ph ...
ing, etc.) can cause the foramen ovale to remain open.


Types

The six types of atrial septal defects 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
fetal A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal develo ...
development.


Ostium secundum

The ostium secundum atrial septal defect is the most common type of atrial septal defect and comprises 6–10% of all congenital heart diseases. It involves a patent ostium secundum (that is, a patent
foramen secundum The foramen secundum, or ostium secundum is a in the septum primum, a precursor to the interatrial septum of the human heart. It is not the same as the foramen ovale, which is an opening in the septum secundum. Development The foramen secund ...
). The secundum atrial septal defect usually arises from an enlarged foramen ovale, inadequate growth of the
septum secundum The septum secundum is a muscular flap that is important in heart development. It is semilunar in shape, and grows downward from the upper wall of the atrium immediately to the right of the septum primum and ostium secundum. It is important in t ...
, or excessive absorption of the
septum primum During heart development of a human embryo, the single primitive atrium becomes divided into right and left by a , the septum primum. The septum primum () grows downward into the single atrium. Development The gap below it is known as the ostiu ...
. About 10 to 20% of individuals with ostium secundum ASDs also have mitral valve prolapse. An ostium secundum ASD accompanied by an acquired
mitral valve stenosis Mitral stenosis is a valvular heart disease characterized by the narrowing of the opening of the mitral valve of the heart. It is almost always caused by rheumatic valvular heart disease. Normally, the mitral valve is about 5 cm2 during d ...
is called
Lutembacher's syndrome Lutembacher's syndrome is a very rare form of congenital heart disease that affects one of the chambers of the heart (commonly the Atrium (heart), atria) as well as a valve (commonly the mitral valve). It is commonly known as both Atrial septal def ...
.


Natural history

Most individuals with an uncorrected secundum ASD do not have significant symptoms through early adulthood. More than 70% develop symptoms by about 40 years of age. Symptoms are typically decreased exercise tolerance, easy fatigability,
palpitation Palpitations are perceived abnormalities of the heartbeat characterized by awareness of cardiac muscle contractions in the chest, which is further characterized by the hard, fast and/or irregular beatings of the heart. Symptoms include a rapi ...
s, and syncope. Complications of an uncorrected secundum ASD include pulmonary hypertension, right-sided
congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...
. 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 syndrome Eisenmenger syndrome or Eisenmenger's syndrome is defined as the process in which a long-standing left-to-right cardiac shunt caused by a congenital heart defect (typically by a ventricular septal defect, atrial septal defect, or less commonly, pat ...
occurs in 5 to 10% of individuals late in the disease process.


Patent foramen ovale

A patent foramen ovale (PFO) is a remnant opening of the fetal foramen ovale, which normally closes after a person's birth. In medical use, the term "patent" means open or unobstructed. In about 25% of people, the foramen ovale fails to close properly, leaving them with a PFO or at least with what some physicians classify as a "pro-PFO", which is a PFO that is normally closed, but can open under increased blood pressure. On echocardiography, shunting of blood may not be noted except when the patient coughs. PFO is linked to
stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
,
sleep apnea Sleep apnea, also spelled sleep apnoea, is a sleep disorder in which pauses in breathing or periods of shallow breathing during sleep occur more often than normal. Each pause can last for a few seconds to a few minutes and they happen many tim ...
,
migraine Migraine (, ) is a common neurological disorder characterized by recurrent headaches. Typically, the associated headache affects one side of the head, is pulsating in nature, may be moderate to severe in intensity, and could last from a few hou ...
with aura, cluster headache,
decompression sickness Decompression sickness (abbreviated DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompressio ...
, Raynaud's phenomenon, hyperventilation syndrome, transient global amnesia (TGA), and leftsided carcinoid heartdisease (mitral valve). No cause is established for a foramen ovale to remain open instead of closing naturally, but heredity and genetics may play a role. In rats research showed a link to the amount of Cryptosporidium infestation and the number of newborn rats that failed to close their foramen ovale rticle in Russian PFO is not treated in the absence of other symptoms. The mechanism by which a PFO may play a role in stroke is called
paradoxical embolism An embolus, is described as a free-floating mass, located inside blood vessels that can travel from one site in the blood stream to another. An embolus can be made up of solid (like a blood clot), liquid (like amniotic fluid), or gas (like air). O ...
. In the case of PFO, a blood clot from the venous circulatory system is able to pass from the right atrium directly into the left atrium via the PFO, rather than being filtered by the lungs, and thereupon into systemic circulation toward the brain. Also multiple substances -including the prothrombotic agent serotonin- are shunted bypassing the lungs. PFO is common in patients with an atrial septal aneurysm (ASA), a much rarer condition, which is also linked to cryptogenic (i.e., of unknown cause) stroke. PFO is more common in people with cryptogenic stroke than in those with a stroke of known cause. While PFO is present in 25% in the general population, the probability of someone having a PFO increases to about 40 to 50% in those who have had a cryptogenic stroke, and more so in those who have a stroke before the age of 55. Treatment with anticoagulant and antiplatelet medications in this group appear similar.


Ostium primum

A defect in the
ostium primum In the developing heart, the atria are initially open to each other, with the opening known as the primary interatrial foramen or ostium primum (or interatrial foramen primum). The foramen lies beneath the edge of septum primum and the endocardi ...
is occasionally classified as an atrial septal defect, but it is more commonly classified as an
atrioventricular septal defect Atrioventricular septal defect (AVSD) or atrioventricular canal defect (AVCD), also known as "common atrioventricular canal" (CAVC) or "endocardial cushion defect" (ECD), is characterized by a deficiency of the atrioventricular septum of the heart ...
. Ostium primum defects are less common than ostium secundum defects. This type of defect is usually associated 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 ...
.


Sinus venosus

A sinus venosus ASD is a type of atrial septum defect in which the defect involves the venous inflow of either the
superior vena cava The superior vena cava (SVC) is the superior of the two venae cavae, the great venous trunks that return deoxygenated blood from the systemic circulation to the right atrium of the heart. It is a large-diameter (24 mm) short length vein th ...
or the
inferior vena cava The inferior vena cava is a large vein that carries the deoxygenated blood from the lower and middle body into the right atrium of the heart. It is formed by the joining of the right and the left common iliac veins, usually at the level of the ...
. 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 vein 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 ...
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 Situs ambiguus is a rare congenital defect in which the major visceral organs are distributed abnormally within the chest and abdomen. Clinically heterotaxy spectrum generally refers to any defect of Left-right asymmetry and arrangement of the visc ...
.


Mixed

The interatrial septum can be divided into five septal zones. If the defect involves two or more of the septal zones, then the defect is termed a mixed atrial septal defect.


Presentation


Complications

Due to the communication between the atria that occurs in ASDs, disease entities or complications from the condition are possible. Patients with an uncorrected atrial septal defect may be at increased risk for developing a cardiac arrhythmia, as well as more frequent respiratory infections.


Decompression sickness

ASDs, and particularly PFOs, are a predisposing venous blood carrying inert gases, such as
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
or
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
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 lungs 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.


Eisenmenger's syndrome

If a net flow of blood exists from the left atrium to the right atrium, called a left-to-right shunt, then an increase in the blood flow through the lungs happens. Initially, this increased blood flow is asymptomatic, but if it persists, the pulmonary blood vessels may stiffen, causing pulmonary hypertension, which increases the pressures in the right side of the heart, leading to the reversal of the shunt into a right-to-left shunt. Reversal of the shunt occurs, and the blood flowing in the opposite direction through the ASD is called Eisenmenger's syndrome, a rare and late complication of an ASD.


Paradoxical embolus

Venous
thrombus A thrombus (plural thrombi), colloquially called a blood clot, is the final product of the blood coagulation step in hemostasis. There are two components to a thrombus: aggregated platelets and red blood cells that form a plug, and a mesh of ...
(clots in the veins) are quite common. Embolizations (dislodgement of thrombi) normally go to the lung and cause pulmonary emboli. In an individual with ASD, these emboli can potentially enter the arterial system, which can cause any phenomenon attributed to acute loss of blood to a portion of the body, including
cerebrovascular accident A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop funct ...
(stroke), infarction of the
spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .
or intestines, or even a distal extremity (i.e., finger or toe). This is known as a paradoxical embolus because the clot material paradoxically enters the arterial system instead of going to the lungs.


Migraine

Some recent research has suggested that a proportion of cases of migraine may be caused by PFO. While the exact mechanism remains unclear, closure of a PFO can reduce symptoms in certain cases. This remains controversial; 20% of the general population has a PFO, which for the most part, is asymptomatic. About 20% of the female population has migraines, and the
placebo effect A placebo ( ) is a substance or treatment which is designed to have no therapeutic value. Common placebos include inert tablets (like sugar pills), inert injections (like Saline (medicine), saline), sham surgery, and other procedures. In general ...
in migraine typically averages around 40%. The high frequency of these facts make finding statistically significant relationships between PFO and migraine difficult (i.e., the relationship may just be chance or coincidence). In a large
randomized controlled trial A randomized controlled trial (or randomized control trial; RCT) is a form of scientific experiment used to control factors not under direct experimental control. Examples of RCTs are clinical trials that compare the effects of drugs, surgical te ...
, the higher prevalence of PFO in migraine patients was confirmed, but migraine headache cessation was not more prevalent in the group of migraine patients who underwent closure of their PFOs.


Causes

*
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 ...
– patients with Down syndrome have higher rates of ASDs, especially a particular type that involves the ventricular wall. As many as one half of Down syndrome patients have some type of septal defect. *
Ebstein's anomaly Ebstein's anomaly is a congenital heart defect in which the septal and posterior leaflets of the tricuspid valve are displaced towards the apex of the right ventricle of the heart. It is classified as a critical congenital heart defect accounting ...
– about 50% of individuals with Ebstein anomaly have an associated shunt between the right and left atria, either an atrial septal defect or a
patent foramen ovale 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 ...
. * Fetal alcohol syndrome – about one in four patients with fetal alcohol syndrome has either an ASD or a
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 ...
. *
Holt–Oram syndrome Holt–Oram syndrome (also called atrio-digital syndrome, atriodigital dysplasia, cardiac-limb syndrome, heart-hand syndrome type 1, HOS, ventriculo-radial syndrome) is an autosomal dominant disorder that affects bones in the arms and hands (the u ...
– both the osteium secundum and osteum primum types of ASD are associated with Holt–Oram syndrome *
Lutembacher's syndrome Lutembacher's syndrome is a very rare form of congenital heart disease that affects one of the chambers of the heart (commonly the Atrium (heart), atria) as well as a valve (commonly the mitral valve). It is commonly known as both Atrial septal def ...
– the presence of a congenital ASD along with acquired mitral stenosis


Mechanisms

In unaffected individuals, the chambers of the left side of the heart are under higher pressure than the chambers of the right side because the left ventricle has to produce enough pressure to pump blood throughout the entire body, while the right ventricle needs only to produce enough pressure to pump blood to the
lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
s. In the case of a large ASD (> 9 mm), which may result in a clinically remarkable left-to-right shunt, blood shunts from the left atrium to the right atrium. This extra blood from the left atrium may cause a volume overload of both the right atrium and the right ventricle. If untreated, this condition can result in enlargement of the right side of the heart and ultimately heart failure. Any process that increases the pressure in the left ventricle can cause worsening of the left-to-right shunt. This includes hypertension, which increases the pressure that the left ventricle has to generate to open the aortic valve during ventricular
systole Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. The term originates, via New Latin, from Ancient Greek (''sustolē''), from (''sustéllein'' 'to contract'; from ''sun ...
, and
coronary artery disease Coronary artery disease (CAD), also called coronary heart disease (CHD), ischemic heart disease (IHD), myocardial ischemia, or simply heart disease, involves the reduction of blood flow to the heart muscle due to build-up of atherosclerotic pla ...
which increases the stiffness of the left ventricle, thereby increasing the filling pressure of the left ventricle during ventricular
diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventric ...
. The left-to-right shunt increases the filling pressure of the right heart (
preload Preload may refer to: Science and technology * Preload (cardiology), maximum stretch of the heart at the end of diastole * preload (software), code-prefetching software for Linux * Preload (engineering), the internal application of stress to cert ...
) and forces the right ventricle to pump out more blood than the left ventricle. This constant overloading of the right side of the heart causes an overload of the entire pulmonary vasculature. Eventually, pulmonary hypertension may develop. The pulmonary hypertension will cause the right ventricle to face increased afterload. The right ventricle is forced to generate higher pressures to try to overcome the pulmonary hypertension. This may lead to
right ventricular failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
(dilatation and decreased systolic function of the right ventricle). If the ASD is left uncorrected, the pulmonary hypertension progresses and the pressure in the right side of the heart becomes greater than the left side of the heart. This reversal of the pressure gradient across the ASD causes the shunt to reverse – a right-to-left shunt. This phenomenon is known as
Eisenmenger's syndrome Eisenmenger syndrome or Eisenmenger's syndrome is defined as the process in which a long-standing left-to-right cardiac shunt caused by a congenital heart defect (typically by a ventricular septal defect, atrial septal defect, or less commonly, pat ...
. Once right-to-left shunting occurs, a portion of the oxygen-poor blood gets shunted to the left side of the heart and ejected to the peripheral vascular system. This causes signs of
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 ...
. Image:Gray468.png, Heart of human
embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
of about 35 days Image:Atrial septal defect-en.png, Atrial septal defect with left-to-right shunt File:Blausen 0069 AtrialSeptalDefect 02.png, Illustration depicting atrial septal defect


Diagnosis

Most individuals with a significant ASD are diagnosed ''
in utero ''In Utero'' is the third and final studio album by American rock band Nirvana. It was released on September 21, 1993, by DGC Records. After breaking into the mainstream with their second album, ''Nevermind'' (1991), Nirvana hired Steve Albin ...
'' or in early childhood with the use of
ultrasonography Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...
or
auscultation Auscultation (based on the Latin verb ''auscultare'' "to listen") is listening to the internal sounds of the body, usually using a stethoscope. Auscultation is performed for the purposes of examining the circulatory and respiratory systems (hea ...
of the heart sounds during
physical examination In a physical examination, medical examination, or clinical examination, a medical practitioner examines a patient for any possible medical signs or symptoms of a medical condition. It generally consists of a series of questions about the pati ...
. Some individuals with an ASD have 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 present with symptoms of dyspnea on exertion (shortness of breath with minimal exercise),
congestive heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, ...
, or
cerebrovascular accident A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop funct ...
(stroke). They may be noted on routine testing to have an abnormal
chest X-ray A chest radiograph, called a chest X-ray (CXR), or chest film, is a projection radiograph of the chest used to diagnose conditions affecting the chest, its contents, and nearby structures. Chest radiographs are the most common film taken in med ...
or an abnormal
ECG Electrocardiography is the process of producing an electrocardiogram (ECG or EKG), a recording of the heart's electrical activity. It is an electrogram of the heart which is a graph of voltage versus time of the electrical activity of the hear ...
and may have atrial fibrillation. If the ASD causes a left-to-right shunt, the pulmonary vasculature in both lungs may appear dilated on chest X-ray, due to the increase in pulmonary blood flow.


Physical examination

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 failure that may be present in these individuals. In unaffected individuals, respiratory variations occur in the splitting of the second heart sound (S2). 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 systole. This causes a normal delay in the P2 component of S2. 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 P2 to occur earlier. In individuals with an ASD, a fixed splitting of S2 occurs because the extra blood return during inspiration gets equalized between the left and right atria 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
echocardiography An echocardiography, echocardiogram, cardiac echo or simply an echo, is an ultrasound of the heart. It is a type of medical imaging of the heart, using standard ultrasound or Doppler ultrasound. Echocardiography has become routinely used in t ...
, 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 vein during echocardiography, small air bubbles can be seen on echocardiographic imaging. Bubbles traveling across an ASD may be seen either at rest or during a cough. (Bubbles only flow from right atrium to left atrium if the right atrial pressure is greater than left atrial). 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 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, use of the echocardiogram to measure the cardiac output of the left ventricle and the right ventricle independently is possible. In this way, the shunt fraction can be estimated using echocardiography.


Transcranial doppler bubble study

A less invasive method for detecting a PFO or other ASDs than transesophagal ultrasound is
transcranial Doppler Transcranial Doppler (TCD) and transcranial color Doppler (TCCD) are types of Doppler ultrasonography that measure the velocity of blood flow through the brain's blood vessels by measuring the echoes of ultrasound waves moving transcranially (th ...
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 block First-degree atrioventricular block (AV block) is a disease of the electrical conduction system of the heart in which electrical impulses conduct from the cardiac atria to the ventricles through the atrioventricular node (AV node) more slowly tha ...
). The prolongation of the PR interval is probably due to the enlargement of the atria 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 The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is an oval shaped region of special cardiac muscle in the upper back wall of the right atrium made up of cells known as pacemaker cells. The sinus node is approximat ...
to the
AV node The atrioventricular node or AV node electrically connects the heart's atria and ventricles to coordinate beating in the top of the heart; it is part of the electrical conduction system of the heart. The AV node lies at the lower back section of t ...
. 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
right bundle branch block A right bundle branch block (RBBB) is a heart block in the right bundle branch of the electrical conduction system. During a right bundle branch block, the right ventricle is not directly activated by impulses travelling through the right bu ...
, which is so characteristic that if it is absent, the diagnosis of ASD should be reconsidered. File:UOTW 54 - Ultrasound of the Week 1.webm, ASD with pulmonary embolism resulting in a right-to-left shunting of blood File:UOTW 54 - Ultrasound of the Week 2.webm, ASD with pulmonary embolism resulting in a right-to-left shunting of blood File:UOTW 54 - Ultrasound of the Week 3.webm, ASD with pulmonary embolism resulting in a right-to-left shunting of blood


Treatment


Patent foramen ovale

Most patients with a PFO are asymptomatic and do not require any specific treatment. However, those who develop a stroke require further workup to identify the etiology. In those where a comprehensive evaluation is performed and an obvious etiology is not identified, they are defined as having a cryptogenic stroke. The mechanism for stroke is such individuals is likely embolic due to paradoxical emboli, a left atrial appendage clot, a clot on the inter-atrial septum, or within the PFO tunnel.


PFO closure

Until recently, patients with PFO and cryptogenic stroke were treated with antiplatelet therapy only. Previous studies did not identify a clear benefit of PFO closure over antiplatelet therapy in reducing recurrent ischemic stroke. However, based on new evidence and systematic review in the field, percutaneous PFO closure in addition to antiplatelet therapy is suggested for all who meet all the following criteria: * Age ≤ 60 years at onset of first stroke, *
Embolic An embolism is the lodging of an embolus, a blockage-causing piece of material, inside a blood vessel. The embolus may be a blood clot (thrombus), a fat globule ( fat embolism), a bubble of air or other gas (gas embolism), amniotic fluid ( amni ...
-appearing cryptogenic
ischemic stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
(i.e., no evident source of stroke despite a comprehensive evaluation), and * PFO with a right-to-left interatrial shunt detected by bubble study (echocardiogram) A variety of PFO closure devices may be implanted via catheter-based procedures.


Medical therapy

Based on the most up to date evidence, PFO closure is more effective at reducing recurrent ischemic stroke when compared to medical therapy. In most of these studies, antiplatelet and anticoagulation were combined in the medical therapy arm. Although there is limited data on the effectiveness of anticoagulation in reducing stroke in this population, it is hypothesized that based on the embolic mechanism, that anticoagulation should be superior to antiplatelet therapy at reducing risk of recurrent stroke. A recent review of the literature supports this hypothesis recommending anticoagulation over the use of antiplatelet therapy in patients with PFO and cryptogenic stroke. However, more evidence is required comparing of PFO closure with anticoagulation or anticoagulation with antiplatelet therapy.


Atrial septal defect

Once someone is found to have an atrial septal defect, a determination of whether it should be corrected is typically made. If the atrial septal defect is causing the right ventricle to enlarge a secundum atrial septal defect should generally be closed. If the ASD is not causing problems the defect may simply be checked every two or three years. 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. Pulmonary hypertension is not always present in adults who 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 superior vena cava, inferior vena cava, right atrium, right ventricle, and pulmonary artery, and in the wedge position. Individuals with a pulmonary vascular resistance (PVR) less than 7 wood units show regression of symptoms (including NYHA functional class). However, individuals with a PVR greater than 15 wood units have increased mortality associated with closure of the ASD. If the pulmonary arterial pressure is more than two-thirds of the systemic systolic pressure, a net left-to-right shunt should occur 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, the right-to-left shunt must be shown to be reversible with pulmonary artery vasodilators prior to surgery.) 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 less than 40 mmHg. If
Eisenmenger's syndrome Eisenmenger syndrome or Eisenmenger's syndrome is defined as the process in which a long-standing left-to-right cardiac shunt caused by a congenital heart defect (typically by a ventricular septal defect, atrial septal defect, or less commonly, pat ...
has occurred, a significant risk of mortality exists 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 afterload 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.


Surgical closure

Surgical closure of an ASD involves opening up at least one atrium and closing the defect with a patch under direct visualization.


Catheter procedure

Percutaneous device closure involves the passage of a catheter into the heart through the femoral vein guided by fluoroscopy and echocardiography. An example of a percutaneous device is a device which has discs that can expand to a variety of diameters at the end of the catheter. The catheter is placed in the right femoral vein and guided into the right atrium. The catheter is guided through the atrial septal wall and one disc (left atrial) is opened and pulled into place. Once this occurs, the other disc (right atrial) is opened in place and the device is inserted into the septal wall. This type of PFO closure is more effective than drug or other medical therapies for decreasing the risk of future thromboembolism. The most common adverse effect of PFO device closure is new-onset atrial fibrillation. Other complications, all rare, include device migration, erosion and embolization and device thrombosis or formation of an inflammatory mass with risk for recurrent ischemic stroke. 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 superior vena cava, inferior vena cava, or the
tricuspid The tricuspid valve, or right atrioventricular valve, is on the right dorsal side of the mammalian heart, at the superior portion of the right ventricle. The function of the valve is to allow blood to flow from the right atrium to the right ven ...
or
mitral The mitral valve (), also known as the bicuspid valve or left atrioventricular valve, is one of the four heart valves. It has two cusps or flaps and lies between the left atrium and the left ventricle of the heart. The heart valves are all one-w ...
valves. The Amplatzer 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– to 0.005-inch 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. Studies evaluating percutaneous ASD closure among pediatric and adult population show that this is relatively safer procedure and has better outcomes with increasing hospital volume.


Epidemiology

As a group, atrial septal defects are detected in one child per 1500 live births. PFOs are quite common (appearing in 10–20% of adults), but when asymptomatic go undiagnosed. ASDs make up 30 to 40% of all congenital heart diseases that are seen in adults. The ostium secundum atrial septal defect accounts for 7% of all congenital heart lesions. This lesion shows a male:female ratio of 1:2.


References


Additional references

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Further reading

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External links


Atrial septal defect
information for parents. {{DEFAULTSORT:Atrial Septal Defect Congenital heart defects Diving medicine