Overview
Definition:
An atrial septal defect (ASD) is a congenital heart anomaly characterized by a persistent opening in the septum separating the left and right atria, allowing blood to shunt from the left atrium to the right atrium.
Epidemiology:
ASD is one of the most common congenital heart defects, accounting for approximately 5-10% of all cases
The prevalence varies, with some studies suggesting a higher incidence in females
Secundum ASDs are the most frequent type, comprising 70-80% of all ASDs.
Clinical Significance:
Unrepaired ASDs can lead to right atrial and right ventricular volume overload, pulmonary hypertension, atrial arrhythmias (especially atrial fibrillation/flutter in adults), and potentially Eisenmenger syndrome in severe, untreated cases
Timely diagnosis and management are crucial for preventing long-term sequelae and improving patient outcomes.
Clinical Presentation
Symptoms:
Many small ASDs are asymptomatic and discovered incidentally
Larger defects or those with significant shunting may present with exertional dyspnea
Fatigue
Recurrent respiratory infections
Poor growth (failure to thrive) in infants
Palpitations or syncope (more common in adults due to arrhythmias).
Signs:
A characteristic finding is a widely split and fixed second heart sound (S2)
A systolic ejection murmur may be heard at the left upper sternal border due to increased flow across the pulmonic valve
A diastolic rumble may be present at the lower left sternal border if the tricuspid valve flow is significantly increased.
Diagnostic Criteria:
Diagnosis is primarily based on clinical examination, echocardiography, and electrocardiography
Echocardiography (transthoracic and transesophageal) is the gold standard for diagnosis, quantifying shunt size, direction, and pressure gradients, and assessing associated anomalies
Cardiac catheterization may be used for precise hemodynamic measurements and pre-procedural planning in complex cases.
Diagnostic Approach
History Taking:
Detailed birth history including perinatal complications
History of recurrent pneumonias or feeding difficulties in infants
Presence of exertional dyspnea, fatigue, or palpitations
Family history of congenital heart disease
Inquiry about prior cardiac evaluations.
Physical Examination:
Assess vital signs including heart rate, blood pressure, respiratory rate, and oxygen saturation
Auscultate heart sounds for the characteristic S2 splitting and murmurs
Palpate for thrills
Examine for signs of right heart enlargement (e.g., hepatomegaly)
Evaluate for peripheral edema
Assess growth parameters.
Investigations:
Electrocardiogram (ECG): May show right axis deviation and right bundle branch block (RBBB) in secundum ASD
Echocardiography (2D, Doppler, Color Doppler): Confirms diagnosis, determines ASD type and size, measures shunt volume (Qp:Qs ratio), assesses chamber sizes and RV function
Chest X-ray: May show cardiomegaly and prominent pulmonary arteries in larger shunts
Cardiac MRI/CT: Useful for complex anatomy or evaluating residual shunts
Cardiac Catheterization: Primarily for hemodynamic assessment and interventional planning if echocardiography is inconclusive or complex intervention is planned.
Differential Diagnosis:
Other causes of a systolic ejection murmur at the left upper sternal border (e.g., pulmonic stenosis, innocent flow murmur)
Other causes of fixed split S2 (e.g., pulmonary hypertension)
Other causes of dyspnea in children (e.g., asthma, pneumonia)
Other causes of heart failure symptoms.
Management
Initial Management:
For asymptomatic or hemodynamically insignificant ASDs, observation may be appropriate
For symptomatic patients or those with significant shunting, closure is indicated.
Medical Management:
Primarily supportive and aimed at managing complications
Diuretics may be used for heart failure symptoms
Beta-blockers or antiarrhythmics may be required for atrial arrhythmias
Anticoagulation might be considered for patients with atrial fibrillation, especially post-closure.
Device Closure:
Indications: Secundum ASDs with Qp:Qs ratio > 1.5:1 and significant left atrial/ventricular volume overload, absence of significant pulmonary hypertension, suitable anatomy for device deployment
Contraindications: Significant pulmonary hypertension with RV dysfunction, multiple or very large defects, restrictive interatrial communication, severe associated intracardiac anomalies requiring surgery
Procedure: Transcatheter closure using devices (e.g., Amplatzer Septal Occluder) inserted via femoral venous access
Advantages: Minimally invasive, faster recovery, reduced hospital stay, lower morbidity
Disadvantages: Risk of device embolization, atrial/ventricular perforation, arrhythmias, systemic embolization (rare), late erosion or thrombus formation.
Surgical Management:
Indications: ASDs not amenable to device closure (e.g., primum, sinus venosus, coronary sinus ASDs), complex associated congenital heart defects requiring surgical repair, significant pulmonary hypertension with RV dysfunction where surgical decompression is beneficial, failed device closure
Procedure: Open-heart surgery involving cardiopulmonary bypass
The ASD is closed with sutures or a pericardial/dacron patch
Advantages: Definitive repair for complex ASD types and associated anomalies
Disadvantages: More invasive, longer hospital stay, higher risk of surgical complications (e.g., bleeding, infection, phrenic nerve injury, sternal dehiscence).
Supportive Care:
Regular clinical follow-up is essential after closure, regardless of method
Echocardiographic monitoring to assess for residual shunt, chamber size normalization, and device integrity
Patient education on potential late complications and need for endocarditis prophylaxis if indicated.
Complications
Early Complications:
Device Closure: Arrhythmias (e.g., junctional tachycardia during deployment), vascular access complications (hematoma, bleeding), transient AV block, device embolization
Surgery: Bleeding requiring re-operation, cardiac tamponade, wound infection, pneumonia, pleural effusion, phrenic nerve palsy, stroke.
Late Complications:
Device Closure: Atrial arrhythmias (supraventricular tachycardia, atrial fibrillation), device migration or embolization, incomplete closure, device erosion into adjacent structures, thrombus formation on the device
Surgery: Residual or recurrent shunting, arrhythmias, pulmonary hypertension, infective endocarditis, right ventricular dysfunction.
Prevention Strategies:
Careful patient selection for device closure based on anatomical suitability
Meticulous surgical technique
Appropriate anticoagulation post-procedure (if indicated)
Long-term surveillance with echocardiography to detect early signs of complications
Prompt management of arrhythmias.
Prognosis
Factors Affecting Prognosis:
Age at diagnosis and intervention, size of the defect and shunt volume, presence of pulmonary hypertension, degree of ventricular dysfunction, presence of associated cardiac anomalies, development of arrhythmias, success of closure (complete seal).
Outcomes:
Successful closure of ASDs typically leads to normalization of cardiac hemodynamics, reversal of chamber enlargement, and improved exercise tolerance
For most patients, prognosis after successful closure is excellent, with a life expectancy comparable to the general population
However, patients with significant pre-existing pulmonary hypertension or those who undergo closure in adulthood may have a less favorable outcome.
Follow Up:
Routine follow-up is recommended, especially in the initial post-closure period
Echocardiography is typically performed at 1, 6, and 12 months post-closure, then annually or biennially
Longer follow-up may be required for patients with residual shunts, significant pulmonary hypertension, or arrhythmias
Device closure patients may require endocarditis prophylaxis for 6 months post-procedure.
Key Points
Exam Focus:
Distinguish between secundum, primum, sinus venosus, and coronary sinus ASDs
Understand the hemodynamic consequences of left-to-right shunting
Differentiate indications for device closure vs
surgical repair
Recognize ECG findings (RBBB, right axis deviation)
Key investigations: Echo (Qp:Qs, RV size), ECG
Complications of both methods are high-yield.
Clinical Pearls:
A fixed split S2 in a young child with a murmur at the LUSB is highly suggestive of ASD
Always evaluate for associated anomalies, especially with primum and sinus venosus ASDs
Qp:Qs > 1.5:1 on Doppler is a common threshold for considering closure
Consider patient age and anatomy when choosing between device and surgery.
Common Mistakes:
Misinterpreting an innocent murmur as pathological or vice versa
Underestimating the significance of a fixed split S2
Failing to assess for associated cardiac lesions
Incorrectly selecting patients for device closure when surgery is more appropriate
Inadequate follow-up leading to missed late complications.