Makindo Medical Notes

Related Subjects: |Congenital Acyanotic Heart Disease |Congenital Cyanotic Heart Disease |Cardiac Embryology |Cyanosis - Central and Peripheral |Down's syndrome (Trisomy 21) |Tetralogy of Fallot |Patent Foramen Ovale (PFO) |Ventricular Septal defect (VSD) |Atrial Septal defect (ASD)

In an ASD, the primary murmur is not due to the flow across the septal defect itself but results from increased right-sided flow, leading to an ejection systolic murmur (ESM) over the pulmonary valve. The risk of endocarditis is low. Surgical intervention is considered if the pulmonary-to-systemic flow ratio (Qp:Qs) is greater than 1.5.

About

• Atrial Septal Defect (ASD) is a congenital heart defect where there is an abnormal opening between the atria, allowing blood to shunt from the left atrium (LA) to the right atrium (RA).
• Results in left-to-right shunting, increasing the flow of oxygenated blood into the right side of the heart and pulmonary circulation.
• ASDs account for about 10% of congenital heart defects, with a higher incidence in females and individuals with Down's syndrome.

Aetiology

• The left-to-right shunt in ASD leads to increased pulmonary blood flow and right heart volume overload.
• The magnitude of the shunt is determined by the size of the defect and the relative compliance of the left and right atria.
• Over time, the right atrium and right ventricle can become dilated, leading to heart failure if left untreated.
• As pulmonary blood flow increases, patients may develop pulmonary hypertension and complications like right heart failure.

Types of ASDs

• Ostium Secundum (70%): The most common type, typically involving the region of the foramen ovale. Often associated with mitral valve prolapse. ECG findings include RBBB with right axis deviation (RAD).
• Ostium Primum (15%): More serious, involving defects near the atrioventricular (AV) valves, resulting in a partial AV septal defect (pAVSD). May present with mitral and tricuspid regurgitation. ECG findings include RBBB with left axis deviation (LAD) and first-degree AV block. Associated with Down's syndrome, Noonan syndrome, and Klinefelter syndrome.
• Sinus Venosus (15%): Involves defects near the superior vena cava (SVC) or inferior vena cava (IVC), often with anomalous pulmonary venous return. ECG may show RBBB.
• Unroofed Coronary Sinus (<1%): A rare defect where the coronary sinus is connected to the left atrium, leading to a left-to-right shunt.

Pathophysiology

• With an ASD, oxygen-rich blood from the LA flows into the RA, leading to right atrial and right ventricular volume overload.
• This increased right-sided flow can cause right atrial dilation, right ventricular hypertrophy, and over time, right heart failure.
• Chronic volume overload can lead to pulmonary vascular remodeling, pulmonary hypertension, and ultimately Eisenmenger's syndrome if left untreated.

Clinical Presentation

• ASDs are often asymptomatic in childhood and may go undiagnosed until later in life.
• Symptoms: Dyspnoea, fatigue, recurrent respiratory infections, and palpitations due to atrial arrhythmias (e.g., atrial fibrillation).
• Physical Exam: Fixed splitting of the second heart sound (S2) due to delayed right ventricular emptying. Ejection systolic murmur over the left upper sternal border due to increased flow across the pulmonary valve. Mid-diastolic murmur may be heard at the lower left sternal edge due to increased flow across the tricuspid valve.
• Signs of Right Heart Failure: Raised JVP, hepatomegaly, and peripheral edema may be seen in advanced cases.

Investigations

• CXR: May show cardiomegaly, increased pulmonary vascular markings, and an enlarged right atrium and right ventricle.
• ECG:
  • Ostium Secundum: Right bundle branch block (RBBB) with right axis deviation (RAD).
  • Ostium Primum: RBBB with left axis deviation (LAD) and first-degree AV block.
• Echocardiography: The primary diagnostic tool for visualizing the defect, assessing the shunt size, and determining the impact on right heart chambers. It can also identify associated anomalies such as mitral or tricuspid valve involvement.
• Cardiac MRI: Provides detailed anatomy, especially useful in complex or sinus venosus defects.
• Right Heart Catheterization: Used to measure the pulmonary-to-systemic flow ratio (Qp:Qs) and assess pulmonary artery pressures.

Complications

• Pulmonary Hypertension: Increased pulmonary blood flow over time can cause increased pulmonary artery pressures.
• Atrial Arrhythmias: Such as atrial fibrillation and atrial flutter, increasing the risk of thromboembolism and stroke.
• Right Heart Failure: Chronic volume overload can lead to right ventricular failure.
• Paradoxical Embolism: Risk of thromboembolism passing through the defect and causing stroke or systemic embolism.
• Eisenmenger Syndrome: If left untreated, increased pulmonary pressures can reverse the shunt direction, leading to cyanosis and severe complications.

Management

• Monitoring: Small, asymptomatic ASDs may be monitored with regular echocardiography if the right heart is not significantly dilated.
• Surgical Indications: Closure is recommended if the pulmonary-to-systemic flow ratio (Qp:Qs) is greater than 1.5 or if there is evidence of right heart enlargement.
• Catheter-based Closure:
  • Secundum ASDs can be closed using a device inserted percutaneously during cardiac catheterization.
  • Less invasive than open surgery, with shorter recovery times.
• Surgical Closure:
  • Indicated for large secundum ASDs or complex defects like ostium primum or sinus venosus ASDs, which are not suitable for device closure.
  • Open-heart surgery is often required for these defects, with low operative mortality (<1%) in experienced centers.
• Anticoagulation: Considered in patients with atrial fibrillation or those with a history of paradoxical embolism.
• Long-term Prognosis: Excellent if treated before significant pulmonary hypertension develops, but lifelong follow-up is needed to monitor for complications.

References

• AHA/ACC Guidelines for the Management of Patients with Atrial Septal Defects