The heart is divided into four distinct chambers, separated by tight walls called septa, and valves that direct bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood in the right direction.
It can be compared to a house with several rooms, and doors that allow movement from one to another.
A Small Opening Inside the Heart
An atrial septal defect, commonly abbreviated “ASD,” is an abnormal opening in the wall that separates the two upper chambers of the heart: the atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles..
When an atrial septal defect is present, its significance may vary. Its size, shape, and location within the interatrial septum differ from one individual to another.
A Condition Present From Birth
An ASD is a congenital abnormality, meaning it is present at birth.
During the first weeks of embryonic development, the heart gradually forms. Initially, there is only one primitive atrium, which later divides into two distinct chambers: the right atrium and the left atrium.
This separation occurs through the formation of a wall called the interatrial septum.
The development of this septum takes place in several stages. If one of these stages is incomplete or disrupted, an opening may persist between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles..
This explains why different types of atrial septal defects exist.
Not to Be Confused With a Patent Foramen Ovale
It is important to distinguish these true “structural formation abnormalities” of the interatrial septum from another phenomenon: the failure of closure of an opening that is normal during fetal life.
In the fetus, a natural communication exists between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles.. After birth, this opening usually closes spontaneously.
When it remains partially open, it is referred to as a patent foramen ovale (PFO).
Read: Patent Foramen Ovale
What Does This Actually Mean?
At birth, bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood circulation follows a well-organized path through the bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood vessels, the heart, and the lungs.
BloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood moves in one direction only, without flowing backward.
The presence of an atrial septal defect alters this normal pathway.
The opening between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles. creates an additional passage within the heart itself: bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood can then move from one atrium to the other.
Because pressure is normally higher in the left atrium than in the right atrium, a portion of oxygenated bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood returning from the lungs is diverted to the right side through the ASD.
This oxygen-rich bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood is added to the venous bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood already present in the right atrium.
A Progressive Overload
This additional volume results in extra work for the right-sided chambers of the heart.
Depending on the size of the defect and the amount of blood that “recirculates” unnecessarily through the lungs, the right atrium and right ventricle may gradually enlarge.
In other words, the larger the shunt, the harder the right side of the heart must work.
What Are the Possible Symptoms?
An atrial septal defect is present from birth. However, it most often remains silent for many years.
When the opening is very small, it may never cause symptoms.
If the defect is larger, there is usually a long symptom-free period. Signs may appear gradually, sometimes only in adulthood, and even after the age of 40.
Possible symptoms include:
- unusual fatigue
- palpitations“Palpitation” is a symptom related to an abnormality in heartbeats. There are several types of arrhythmias. This term is like a surname that encompasses several first names.
- reduced exercise tolerance
- shortness of breath
- swelling of the legs
The severity and timing of symptoms depend mainly on the size of the opening and the workload imposed on the right side of the heart over time.
Discovery on examination and confirmation of the diagnosis
In many cases, an atrial septal defect is discovered during a routine medical examination.
When listening to the heart, the healthcare professional may detect a heart murmur, usually related to increased bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood flow through the right heart chambers rather than the direct passage of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood across the opening.
Read: Heart murmur
This finding generally leads to an echocardiogram, which is the reference test to confirm the diagnosis. It allows visualization of the opening between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles., measurement of its size, analysis of the direction of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood flow, and assessment of its impact on the right side of the heart.
An atrial septal defect may also be discovered incidentally, during an echocardiogram performed for an entirely different reason.
Cardiac Magnetic Resonance Imaging
In certain situations, cardiac magnetic resonance imaging (cardiac MRI) may be requested.
This test provides additional information, particularly regarding the anatomy of the pulmonary veins — the vessels that carry oxygenated bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood from the lungs back to the left atrium.
In some types of atrial septal defects, these veins may have an abnormal connection, which influences management.
Cardiac Catheterization: Measuring the True Impact
Thanks to advances in echocardiography and cardiac MRI, cardiac catheterization is no longer used to establish the diagnosis of an atrial septal defect.
However, it may be considered in specific situations to more precisely assess the consequences of the ASD on heart function, particularly on the right-sided chambers.
When imaging studies do not allow a clear evaluation of the magnitude of the abnormal blood flow and its real impact on the right heart, catheterization can be used to directly measure pressures within the heart chambers and the pulmonary arteries.
These measurements help determine whether the overload affecting the right side of the heart is significant and whether closure of the defect is justified.
What Should Be Done When an ASD Is Present?
Management of an atrial septal defect depends primarily on its size and its effects on the heart, especially on the right atrium and right ventricle.
- No intervention is required in many situations
In the absence of symptoms and when the right-sided chambers show no enlargement, intervention is generally not required.
In such situations, periodic follow-up is sufficient. Individuals can lead a normal life, including participation in appropriate physical activity and, for women, pregnancy when medical evaluation is reassuring.
- Closure may be recommended when the defect affects the heart
An intervention may be recommended when symptoms attributable to the ASD are present or when cardiologic evaluation shows enlargement of the right-sided chambers, indicating that the defect is affecting heart function.
Two Types of Procedures
Depending on the size and location of the opening, two approaches are possible: open-heart surgery or a percutaneous intervention performed using catheters.
ASDs located in the central portion of the interatrial septum, called ostium secundum defects, represent the most common form of this congenital abnormality.
In adults, the majority of ostium secundum ASDs can be closed percutaneously, meaning without open-heart surgery.
Read: Percutaneous ASD Closure
However, some ostium secundum defects, due to their size or location, cannot be treated with a catheter and require surgical repair.
Other types of atrial septal defects, known as ostium primum and sinus venosus defects, generally require surgical correction because of their location within the septum or associated anatomical features.
Approximately 30 to 40% of ASDs requiring closure are treated surgically.
Read: Surgical ASD Closure
In Summary
An atrial septal defect (ASD) is a congenital abnormality characterized by an opening between the two atriaThe atria are the two upper chambers of the heart. They act as reservoirs for blood that will fill the ventricles. of the heart.
Often silent for many years, it may go unnoticed until adulthood. Its significance depends mainly on the amount of bloodBlood is composed of red blood cells, white blood cells, platelets, and plasma. Red blood cells are responsible for transporting oxygen and carbon dioxide. White blood cells make up our immune defense system. Platelets contribute to blood that abnormally flows toward the right side of the heart and on the additional workload this imposes over time.
When the opening is small and has no impact on the right-sided chambers, simple monitoring is sufficient. However, if enlargement of the right heart or symptoms develop, closure may be recommended.
Thanks to modern techniques, many atrial septal defects can be corrected through a percutaneous approach, without open-heart surgery. In other cases, surgical intervention remains necessary.
Appropriate cardiologic follow-up ensures proper management and helps prevent long-term complications.
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