Atrial Septal Defects (ASDs) Overview

Atrial Septal Defects (ASDs)

• ASDs are abnormal openings in the interatrial septum.
• Ostium secundum ASDs are the most common type, located in the mid portion of the septum.
  • Associated with hemodynamic mitral valve prolapse.
  • More common in women.
• Ostium primum ASDs are located at the inferior portion of the septum.
  • Associated with cleft mitral valve.
• Sinus venosus ASDs are located in the posterior and superior portion of the septum near the SVC or inferior and posterior near the IVC.
  • Associated with partial or total anomalous pulmonary venous return.
  • Usually, a single vein returns blood to the RA instead of the LA.
• Coronary sinus ASDs occur when the roof of the coronary sinus is partially or completely absent, creating a shunt between both atria and the coronary sinus.
  • Dilated coronary sinus can affect the mitral valve.
• Common atrium involves the absence of the interatrial septum.
  • Associated with situs abnormalities.
• Shunts in ASDs are predominantly left to right, with brief reversal during atrial relaxation.

Pathophysiology of ASDs

• Interatrial communication caused by the ASD results in left to right shunting, initially, due to the lower compliance of the RV compared to the LV.
• Prolonged large volume shunting can lead to right to left shunting with elevated right-sided pressures.
  • Eisenmenger's physiology is rare in ASD but can occur when this prolonged large-volume shunting results in right to left flow with increased right-sided pressures.
• Conditions that increase left to right shunting through an ASD:
  • LVH
  • Cardiomyopathy
  • Mitral Stenosis/Regurgitation
  • Mitral Valve Atresia
  • Cor Triatriatum Sinister
  • Aortic Stenosis
  • Coarctation of the Aorta

Clinical Presentation of ASDs

• May be asymptomatic for many years, even into mid to late adulthood.
• Dyspnea upon exertion.
• Recurrent respiratory infections.
• Atrial arrhythmias, especially atrial fibrillation.
• Systolic murmur due to increased flow across the pulmonary valve.
• Relative pulmonary valve stenosis
• A diastolic murmur through the tricuspid valve in cases of large shunts.

Associated Lesions

• Secundum ASD and PFO:
  • Mitral valve prolapse
  • Tricuspid atresia
• Sinus venosus defect:
  • Anomalous pulmonary vein return:
    • Total or partial
    • Right upper and lower pulmonary veins returning to the SVC, RA, or LA.
• Primum ASD:
  • Cleft mitral valve: slit-like hole in a leaflet.
  • Atrioventricular valvular regurgitation.

Etiology

• ASDs occur in approximately 1 in 1000 births.

Echocardiographic Features of ASDs

• 2D/M-mode:

  • Location and size of the defect:
    • Defects greater than 10mm are considered large;
    • 2-20mm is an ideal size for closure;
    • Greater than 25mm is difficult to close.
  • RV function:
    • Dilatation,
    • RVOT diameter (normal 1.7-2.3 cm),
    • Volume and pressure overload (paradoxical septal motion/flattening).
  • Right and left atrial dilatation:
    • LAE is associated with left heart failure, cleft mitral valve, or mitral valve prolapse.
  • Pulmonary artery and branch dilatation.
  • Tricuspid and pulmonic valve annulus dilatation over time.
    • Tricuspid annulus (RV basal measurement) greater than 42mm.
  • Partial or total anomalous venous return.

• Doppler:

  • Color and PW:
    • Demonstrates direction and velocity of the shunt.
    • Turbulent flow in the pulmonary artery due to increased volume.
    • Presence and severity of valvular regurgitation or stenosis.
    • Presence of partial or total anomalous venous return.
    • RVOT VTI is increased with large ASDs; LVOT VTI is decreased with large ASDs. (Higher blood volume = higher VTI; Lower blood volume = lower VTI).
  • Qp/Qs (pulmonary to systemic flow ratio):
    • Hemodynamically significant if greater than or equal to 1.5:1.
    • Helps quantify the degree of shunt across a defect, and is used to determine if and when the defect should be closed.
  • SPAP, MPAP, PAEDP, PVR: obtained from Doppler.
  • Width of the ASD: measured with color Doppler.
  • Left atrial pressure: measured with color Doppler.
  • Right/Left ventricular function: assessed diastole and systole.

Imaging Techniques

• Subcostal imaging is usually optimal for evaluation.
• Pediatric high right parasternal/supraclavicular views may be attempted.
• Crab view:
  • Short axis of SSN for pulmonary vein connection.
• Bubble study:
  • Detects PFO and ASD.
  • Saline injection temporarily increases pressures on the right side, forcing bubbles to appear on the left side of the heart within 3 to 4 cardiac cycles.
    • Late appearance indicates intra-pulmonary shunting.
  • Evaluates for persistent SVC.

Treatment

• Catheterization
• Antiarrhythmics
• Device closure (PFO/Secundum ASD)
• Surgical:
  • Primary (suture) closure for small defects.
  • Patch repair.
• Mitral valve repair or replacement if cleft mitral valve is present.