Atrial Septal Defect (ASD)

• Atrial septal defect (ASD) is a congenital heart defect where there's an abnormal opening in the septum between the heart's two upper chambers (atria).
• This opening allows blood to flow from the left atrium to the right atrium (left-to-right shunt).

Types of ASD

• Secundum ASD: The most common type, located in the center of the atrial septum in the area of the fossa ovalis.
• Primum ASD: Located in the lower part of the atrial septum, near the atrioventricular valves. It's often associated with other heart defects, such as cleft mitral valve.
• Sinus Venosus ASD: Occurs in the upper part of the atrial septum, near where the superior vena cava enters the right atrium. It is frequently associated with partial anomalous pulmonary venous return (PAPVR).
• Coronary Sinus ASD: A rare type where part of the wall between the coronary sinus and the left atrium is missing.

Hemodynamics

• In ASD, oxygenated blood shunts from the left atrium to the right atrium due to pressure differences.
• This leads to right atrial and right ventricular volume overload.
• Over time, this volume overload can cause right heart enlargement and pulmonary hypertension.
• The magnitude of the shunt depends on the size of the defect and the relative compliance of the ventricles.

Clinical Presentation

• Many individuals with ASD are asymptomatic, especially early in life.
• Symptoms, when present, may include:
  • Fatigue
  • Shortness of breath, particularly with exertion
  • Palpitations
  • Frequent respiratory infections in childhood
  • Stroke (paradoxical emboli)
• In adulthood, uncorrected ASD can lead to:
  • Right heart failure
  • Atrial arrhythmias (atrial fibrillation or flutter)
  • Pulmonary hypertension (Eisenmenger syndrome)

Physical Exam Findings

• A systolic ejection murmur may be heard at the upper left sternal border due to increased flow through the pulmonary valve.
• A fixed, widely split second heart sound (S2) is a classic finding, resulting from delayed closure of the pulmonic valve due to increased right ventricular volume.
• A diastolic rumble may be auscultated at the lower left sternal border, representing increased flow across the tricuspid valve.

Diagnostic Testing

• Echocardiography:
  • Transthoracic echocardiography (TTE) is usually the initial diagnostic test.
  • TTE can visualize the ASD, assess the size and location of the defect, and evaluate the degree of right heart enlargement.
  • Transesophageal echocardiography (TEE) may provide better visualization of the ASD, especially for secundum defects, and is often used to guide device closure.
• Electrocardiogram (ECG):
  • May show right axis deviation, right ventricular hypertrophy, or atrial arrhythmias.
• Chest X-ray:
  • May reveal cardiomegaly and increased pulmonary vascular markings.
• Cardiac Catheterization:
  • Rarely needed for diagnosis but may be performed to assess pulmonary artery pressure and pulmonary vascular resistance, especially in adults.
• Cardiac MRI:
  • Can provide detailed anatomical information and assess the size of the defect and the degree of right heart enlargement.

Management

• Observation: Small ASDs may close spontaneously, particularly in infancy. Regular monitoring with echocardiography is recommended.
• Medical Management:
  • Medications may be used to manage symptoms such as heart failure or arrhythmias.
  • Diuretics can help reduce fluid overload.
  • Antiarrhythmics may be needed to control atrial fibrillation or flutter.
• ASD Closure:
  • Device Closure: Most secundum ASDs can be closed percutaneously using a device such as an Amplatzer Septal Occluder. This is the preferred method due to its less invasive nature.
  • Surgical Closure: Indicated for large ASDs, primum ASDs, sinus venosus ASDs, or when device closure is not feasible. It involves suturing the defect closed or using a patch.

Indications for Closure

• Significant left-to-right shunt (Qp/Qs > 1.5:1). Qp represents pulmonary blood flow, and Qs represents systemic blood flow.
• Evidence of right heart enlargement or dysfunction.
• History of paradoxical embolism.
• To prevent long-term complications such as pulmonary hypertension and right heart failure.

Complications

• Eisenmenger Syndrome: Development of pulmonary hypertension with reversal of the shunt to right-to-left, leading to cyanosis.
• Right Heart Failure: Due to chronic right ventricular volume overload.
• Atrial Arrhythmias: Increased risk of atrial fibrillation and flutter.
• Stroke: Paradoxical emboli can cross the ASD and cause a stroke.
• Infective Endocarditis: Although rare, there is a risk of endocarditis associated with ASDs.

Prognosis

• The prognosis for individuals with ASD is generally good, especially if the defect is closed before significant complications develop.
• Early diagnosis and intervention can prevent long-term sequelae such as pulmonary hypertension and right heart failure.
• Regular follow-up is essential to monitor for arrhythmias or other complications.

Special Considerations

• Pregnancy: Women with uncorrected ASDs are at increased risk of complications during pregnancy, including heart failure and arrhythmias. ASD closure is generally recommended before pregnancy.
• Anesthesia: Patients with ASDs require careful monitoring during anesthesia due to the potential for hemodynamic changes and arrhythmias.