The foramen secundum, or ostium secundum is a in 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 ...

, a precursor to 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 ...

of the

human 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 to t ...

. It is not the same as the foramen ovale, which is an opening in 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 ...

Development

The foramen secundum () is formed from small perforations that develop in the

. The septum primum is a that grows down between the single

primitive atrium The primitive atrium is a stage in the embryonic development of the human heart. It grows rapidly and partially encircles the bulbus cordis; the groove against which the bulbus cordis lies is the first indication of a division into right and left ...

of the developing heart to separate it into left and right atria.Schoenwolf, Gary C., and William J. Larsen. Larsen's Human Embryology. 4th ed. Philadelphia: Churchill Livingstone/Elsevier, 2009. 363. Print.

Closure

Once a baby is born, blood should flow through the lungs, which now function to provide oxygen to the blood. The foramen secundum and foramen ovale act as a shunt where blood bypasses the lungs and does not become oxygenated. To provide proper blood flow as a newborn, the foramen secundum and foramen ovale must close at birth. Since the lungs now require a significant amount of blood flow, the vessels going to and from the lungs undergo dilation. While the

pulmonary artery A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and ...

and

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 ...

are dilating, the

umbilical artery The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord. Structure Development The umbilical arteries supply deoxygenated b ...

and

umbilical vein The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta into the growing fetus. The umbilical vein provides convenient access to the central circulation of a neonate for restoration of blood v ...

are severed at the cutting of the

umbilical cord In placental mammals, the umbilical cord (also called the navel string, birth cord or ''funiculus umbilicalis'') is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologi ...

, or the funiculus umbilicalis. This combination results in a reversal of pressure differences between the atria, and the septum primum is permanently forced against the septum secundum. This holds true even during atrial

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 ventri ...

, when the pressure is significantly less than atrial systole.

Function

The septum primum is on the left side of the heart in the

left atrium The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves. There are two at ...

while the septum secundum is much thicker and is located on the right side, in the

right atrium The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves. There are two at ...

. During development, blood shunts from the floor of the right atrium through the foramen ovale in the septum secundum then up through the foramen secundum in the septum primum. The foramen secundum is positioned so that blood exits in the ceiling of the left atrium and then out through 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 ...

and the

aorta The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes o ...

. The position of the foramen secundum and the size of the septum primum are crucial to ensuring that blood not flow backwards from the left atrium to the right atrium. The septum primum, being much thinner, is easily pressed against the septum secundum if blood attempts to flow in the reverse direction, effectively sealing off both the foramen secundum and the foramen ovale.

Clinical significance

An ostium secundum that persists at large size can be a source of

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 ...

s. Foramen secundum atrial septal defects are the most common atrial septal defects. This defect can arise as a result of defects of the septum primum and the septum secundum. For the septum primum, the problem can arise as a result of excess resorption of the septum during the process of apoptosis in order to form the foramen secundum. For the septum secundum, its inadequate growth can cause atrial septal defect since it is supposed to grow and eventually overlap the foramen secundum so as to form the oval foramen. As the right atrial pressure is normally lower than the mean left atrial pressure, a persisting ostium secundum causes usually a left-to-right shunt (meaning that blood flows from the left to the right atrium, wherefore it is an azyanotic heart defect).

Treatment

Newborns with small foramen secundum atrial septal defects have been shown to spontaneously correct by the third or fourth year of life. Therefore, medical supervision is generally accepted as a preventive measure for those diagnosed in infancy, rather than surgical intervention or use of other medical devices. If surgery is required, it is performed using minimally invasive techniques via robotic surgery that often requires only a few days of hospital stay. Surgical intervention should result in full closure of the foramen secundum, and mortality rates are similar to those for

general anesthesia General anaesthesia (UK) or general anesthesia (US) is a medically induced loss of consciousness that renders the patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general ...

. The repair can be made by suturing the atrial septum or, if the foramen secundum is large in size, a patch can be made from the patient's

pericardium The pericardium, also called pericardial sac, is a double-walled sac containing the heart and the roots of the great vessels. It has two layers, an outer layer made of strong connective tissue (fibrous pericardium), and an inner layer made o ...

to fully separate each atrium. The synthetic material

Dacron Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P), is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foo ...

may also be used to create a repair patch. Inserting a catheter has proven to be a safe and successful method for closing the foramen secundum in children. This method avoids the symptoms that accompany most ostium secundum atrial septal defects. The catheter is inserted into the

femoral vein In the human body, the femoral vein is a blood vessel that accompanies the femoral artery in the femoral sheath. It begins at the adductor hiatus (an opening in the adductor magnus muscle) as the continuation of the popliteal vein. It ends a ...

in the leg and moved into place in the atrial septum. Transesophageal echocardiography is accepted as the method to monitor this procedure which, when performed correctly, has shorter recovery times than surgical intervention. Complications of catheter insertion often include nausea and vomiting, blood vessel obstruction, pain, and hemorrhage. The most common problem with this preventive measure is the incomplete closing of the foramen secundum. There is at present no drug therapy for foramen secundum atrial septal defects, although

infective endocarditis Infective endocarditis is an infection of the inner surface of the heart, usually the valves. Signs and symptoms may include fever, small areas of bleeding into the skin, heart murmur, feeling tired, and low red blood cell count. Complications ...

is a postoperative concern. To prevent this condition, a

prophylactic Preventive healthcare, or prophylaxis, consists of measures taken for the purposes of disease prevention.Hugh R. Leavell and E. Gurney Clark as "the science and art of preventing disease, prolonging life, and promoting physical and mental hea ...

is used for six months after the operation.

Prognosis

Many patients with a foramen secundum that persists into adulthood will remain asymptomatic throughout their lives. A mortality rate of less than one tenth of one percent is expected if the operation is performed correctly. Some argue that if the operation is performed before eight years of age, few cardiac abnormalities such as

cardiac dysrhythmia Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adult ...

are expected later in life. Others argue that the operation can take place as late as age 24, to limit cardiac complications in middle age or later. Some sources have argued that mitral regurgitation and mitral valve prolapse are common after age 40, if the ostium secundum is not repaired by age 24. Operative closure of atrial septal defects after age 40, and the ability to diminish symptoms at all remains controversial. Some data does suggest that even after that age, symptoms can be alleviated via surgical intervention, including prevention of

Arrhythmogenic right ventricular dysplasia Arrhythmogenic cardiomyopathy (ACM), arrhythmogenic right ventricular dysplasia (ARVD), or arrhythmogenic right ventricular cardiomyopathy (ARVC), most commonly is an inherited heart disease. ACM is caused by genetic defects of the parts of hea ...

and other associated cardiac abnormalities.

History

The discovery of the formation of the foramen secundum and septum secundum was published by P. N. B. Odgers at the

University of Oxford , mottoeng = The Lord is my light , established = , endowment = £6.1 billion (including colleges) (2019) , budget = £2.145 billion (2019–20) , chancellor ...

in the

Journal of Anatomy The ''Journal of Anatomy'' is a monthly peer-reviewed scientific journal published by Wiley on behalf of the Anatomical Society. It covers all aspects of anatomy and morphology. The journal was first published in 1867 and was originally known as ...

in 1935.Anatomical Society of Great Britain and Ireland. J Anat. 1935 July; 69 (Pt 4): 412–422.5

References

External links

* http://www.mayoclinic.org/atrial-septal-defect/types.html * http://staff.um.edu.mt/acus1/Heart-b.htm {{Authority control Embryology of cardiovascular system