Atrial Septal Defects
Introduction to Atrial Septal Defects
An Atrial Septal Defect (ASD) is a congenital heart defect characterized by an abnormal opening in the atrial septum, allowing blood flow between the left and right atria. ASDs are one of the most common congenital heart defects, accounting for approximately 10-15% of all congenital heart diseases.
The significance of an ASD depends on its size, location, and associated cardiac anomalies. Small ASDs may close spontaneously, while larger defects can lead to right heart volume overload and potential complications if left untreated.
Embryology of Atrial Septal Defects
ASDs result from incomplete formation or resorption of the atrial septum during cardiac development. The atrial septum forms between weeks 4 and 8 of gestation through a complex process involving:
- Septum primum: Grows from the roof of the primitive atrium
- Septum secundum: Develops to the right of the septum primum
- Foramen ovale: A physiological communication between atria in fetal life
Different types of ASDs occur due to abnormalities in various stages of this developmental process. The timing and nature of the disruption determine the specific type and characteristics of the ASD.
Classification of Atrial Septal Defects
ASDs are classified based on their location in the atrial septum:
- Secundum ASD (70-80%):
- Most common type
- Located in the region of the fossa ovalis
- Results from excessive resorption of the septum primum or deficient growth of the septum secundum
- Primum ASD (15-20%):
- Part of the spectrum of atrioventricular septal defects
- Located in the lower part of the atrial septum
- Often associated with cleft mitral valve
- Sinus Venosus ASD (5-10%):
- Superior sinus venosus ASD: Located near the entry of the superior vena cava
- Inferior sinus venosus ASD: Located near the entry of the inferior vena cava
- Often associated with partial anomalous pulmonary venous return
- Coronary Sinus ASD (<1%):
- Rare defect involving the wall between the coronary sinus and the left atrium
- Often associated with a persistent left superior vena cava
Clinical Presentation of Atrial Septal Defects
The clinical presentation of ASDs varies depending on the size of the defect and the resulting hemodynamic changes:
Infants and Young Children:
- Often asymptomatic
- Normal growth and development
- Soft systolic ejection murmur at the upper left sternal border
- Fixed split S2 heart sound
Older Children and Adults:
- Exercise intolerance
- Fatigue
- Palpitations
- Recurrent respiratory infections
- Right ventricular heave
- Signs of right heart failure in advanced cases: peripheral edema, hepatomegaly
Large, long-standing ASDs may lead to pulmonary hypertension and right-to-left shunting (Eisenmenger syndrome) if left untreated, though this is less common than in VSDs.
Diagnosis of Atrial Septal Defects
Diagnosis of ASDs involves a combination of clinical examination and diagnostic tests:
Physical Examination:
- Auscultation: Soft systolic ejection murmur at the upper left sternal border
- Fixed split S2 heart sound
- Right ventricular heave in significant defects
Diagnostic Tests:
- Chest X-ray: May show enlarged right atrium and right ventricle, increased pulmonary vascular markings
- Electrocardiogram (ECG):
- Right axis deviation
- Incomplete right bundle branch block
- Right ventricular hypertrophy in large defects
- Echocardiography: Gold standard for diagnosis
- Transthoracic echocardiography (TTE) to visualize the defect, assess size and location
- Color Doppler to evaluate shunt direction and velocity
- Transesophageal echocardiography (TEE) for better visualization, especially in adults
- Cardiac MRI: Useful for complex anatomy or when echocardiography is inconclusive
- Cardiac Catheterization: Rarely needed for diagnosis, but may be used to assess pulmonary vascular resistance in complex cases
Management of Atrial Septal Defects
Management of ASDs depends on the size of the defect, associated symptoms, and complications:
Conservative Management:
- Small ASDs (especially secundum type) may close spontaneously in childhood
- Regular follow-up with serial echocardiography
- Endocarditis prophylaxis is no longer routinely recommended for isolated ASDs
Indications for Closure:
- Right atrial and right ventricular enlargement
- Significant left-to-right shunt (Qp:Qs > 1.5:1)
- Paradoxical embolism
- Exercise intolerance or decreased functional capacity
Transcatheter Closure:
- Preferred method for secundum ASDs when anatomically suitable
- Devices used include Amplatzer Septal Occluder and Gore CARDIOFORM Septal Occluder
- Less invasive than surgery, shorter hospital stay
Surgical Closure:
- Indicated for:
- Large secundum ASDs not suitable for device closure
- Primum ASDs
- Sinus venosus ASDs
- Coronary sinus ASDs
- Techniques include direct suture closure or patch closure
- Often performed via median sternotomy, minimally invasive approaches are possible in some cases
Timing of Intervention:
- Generally recommended between 2-5 years of age for significant defects
- Can be safely performed in adults, but earlier closure may prevent long-term complications
Complications of Atrial Septal Defects
Untreated or large ASDs can lead to several complications:
- Right Heart Failure: Due to chronic right heart volume overload
- Atrial Arrhythmias: Particularly atrial fibrillation and atrial flutter
- Pulmonary Hypertension: Less common than in VSDs, but can occur in long-standing large defects
- Paradoxical Embolism: Risk of stroke or systemic embolism due to right-to-left shunting
- Eisenmenger Syndrome: Rare in ASDs, but can occur in very large, long-standing defects
Post-closure complications may include:
- Device embolization (in transcatheter closure)
- Residual shunt
- Erosion of adjacent structures
- Thrombus formation on the device
- Post-pericardiotomy syndrome (after surgical closure)
Prognosis of Atrial Septal Defects
The prognosis for patients with ASDs is generally excellent, especially with timely intervention:
- Small ASDs: Excellent prognosis, many close spontaneously
- Closed ASDs (device or surgical): Good long-term outcomes, with most patients leading normal lives
- Life expectancy: Near-normal when closed before the development of pulmonary hypertension
Factors affecting prognosis:
- Size and type of the defect
- Age at closure
- Presence of pulmonary hypertension
- Associated cardiac anomalies
Long-term follow-up is recommended, especially for patients who underwent closure in adulthood or those with residual defects or pulmonary hypertension.
Atrial Septal Defects
- What is an atrial septal defect (ASD)?
A hole in the wall (septum) between the two upper chambers of the heart (atria) - Which type of ASD is the most common?
Secundum ASD - What percentage of congenital heart defects are ASDs?
Approximately 10-15% - Which gender is more commonly affected by ASDs?
Females - What is the embryological cause of a secundum ASD?
Excessive resorption of the septum primum or inadequate development of the septum secundum - What is the most common symptom of a small ASD in children?
Asymptomatic (no symptoms) - Which diagnostic test is considered the gold standard for diagnosing an ASD?
Echocardiogram - What is the Qp:Qs ratio in a hemodynamically significant ASD?
Greater than 1.5:1 - Which complication can occur in untreated large ASDs in adulthood?
Pulmonary hypertension - What is the preferred treatment for a large ASD in a child?
Surgical closure or catheter-based device closure - At what age is elective closure of an ASD typically recommended?
Between 2-5 years of age - What is the success rate of surgical closure of ASDs?
Greater than 95% - Which type of ASD is not suitable for device closure?
Sinus venosus ASD - What is the name of the most commonly used device for transcatheter ASD closure?
Amplatzer Septal Occluder - Which cardiac chamber is typically enlarged in patients with a significant ASD?
Right atrium and right ventricle - What is the characteristic murmur associated with an ASD?
Fixed split S2 with a systolic ejection murmur at the upper left sternal border - Which ECG finding is common in patients with an ASD?
Right axis deviation and right bundle branch block - What is the risk of recurrence of ASD in offspring if a parent has an ASD?
Approximately 4-9% - Which genetic syndrome is associated with a higher incidence of ASDs?
Down syndrome - What is the mortality rate for surgical ASD closure in children?
Less than 1% - Which complication can occur immediately after device closure of an ASD?
Device embolization - What is the long-term survival rate for patients who have undergone ASD closure before age 25?
Nearly normal life expectancy - Which type of ASD is associated with anomalous pulmonary venous return?
Sinus venosus ASD - What is the recommended follow-up interval for patients after ASD closure?
Annual follow-up for the first few years, then every 3-5 years - Which imaging modality can be used to assess ASD size and location if echocardiography is inadequate?
Cardiac MRI or CT - What is the name of the technique used to measure oxygen saturation in different cardiac chambers during catheterization for ASD evaluation?
Oximetry run - Which medication might be prescribed for patients with an ASD and pulmonary hypertension?
Sildenafil or other pulmonary vasodilators - What is the recommended antibiotic prophylaxis duration after device closure of an ASD?
6 months - Which type of ASD is located in the lower part of the atrial septum near the tricuspid valve?
Ostium primum ASD - What is the potential risk of pregnancy in women with an unrepaired large ASD?
Increased risk of paradoxical embolism and heart failure
