EchoAssist™ — ScanCoach
Probe Positioning · Anatomy · Clinical Pearls
View-by-view scanning guides with transducer positioning, normal anatomy, Doppler setup, and clinical pearls — for every modality and patient population.
Atrial Septal Defect
ASD · Diagnosis & Sizing · Any age — often incidental or at routine screening
Anatomy & Pathophysiology
Defect in the interatrial septum allowing left-to-right shunting. Ostium secundum (70%) is the most common type, located in the fossa ovalis. Ostium primum (15–20%) is an atrioventricular septal defect variant at the inferior IAS near the AV valves. Sinus venosus (5–10%) is located at the SVC–RA or IVC–RA junction and is associated with partial anomalous pulmonary venous return (PAPVR). Coronary sinus ASD is rare. Haemodynamic significance depends on defect size, shunt direction, and RV compliance. Qp:Qs >1.5 with RV dilation is the threshold for closure.
Reference Images
Diagram · Clinical EchoClinical Echo Image
Stage Overview — Diagnosis & Sizing
Characterise ASD type, size, and location. Assess shunt direction and magnitude. Evaluate RV dilation and function. Identify associated anomalies (PAPVR, cleft MV in primum ASD).
Key Views
- 1Subcostal — best view for IAS; perpendicular beam avoids dropout artefact
- 2A4C — RV dilation, TR, shunt direction on color Doppler
- 3PSAX — secundum ASD at fossa ovalis; primum at inferior IAS near AV valves
- 4Subcostal bicaval — sinus venosus ASD at SVC–RA junction; PAPVR
- 5PSAX high — right pulmonary veins for PAPVR assessment
Key Measurements
- ▸ASD diameter (subcostal — maximum dimension)
- ▸Rim measurements: aortic rim, posterior rim, inferior rim, superior rim, AV valve rim (all ≥5 mm required for device closure)
- ▸RV end-diastolic dimension (Z-score)
- ▸RV FAC and TAPSE
- ▸Qp:Qs (RVOT VTI × RVOT area / LVOT VTI × LVOT area)
- ▸TR Vmax (RV systolic pressure estimate)
Doppler Protocol
- ◆Color Doppler across IAS — direction and extent of shunt (L→R = left-to-right; R→L = Eisenmenger)
- ◆CW across ASD — mean gradient (low velocity = unrestricted shunt)
- ◆TR CW — RVSP estimate (elevated RVSP = pulmonary hypertension)
- ◆PW RVOT and LVOT — Qp:Qs calculation
- ◆PW at right pulmonary veins — assess for PAPVR (anomalous drainage to SVC or RA)
Normal / Acceptable Criteria
- ✓Secundum ASD: all rims ≥5 mm (suitable for device closure)
- ✓RV dilation proportional to shunt size
- ✓RVSP <40 mmHg (no significant pulmonary hypertension)
- ✓L→R shunt direction (no R→L component)
Red Flags / Reintervention Criteria
- ⚠R→L shunt or bidirectional shunt → pulmonary hypertension / Eisenmenger — urgent cardiology review
- ⚠RVSP >50 mmHg → elevated PA pressure — catheterisation before closure
- ⚠Deficient aortic rim (<5 mm) — may still be closeable with device but requires careful assessment
- ⚠Cleft anterior MV leaflet (primum ASD) — must be repaired surgically, not suitable for device closure
- ⚠PAPVR (sinus venosus ASD) — requires surgical repair, not device closure
Clinical Scanning Tips
Subcostal view is the gold standard for IAS assessment — the ultrasound beam is perpendicular to the septum, eliminating dropout artefact that can mimic an ASD from the A4C view.
Always measure all rims before recommending device closure — a deficient aortic rim (<5 mm) is the most common reason for surgical referral in secundum ASD.
Sinus venosus ASD is frequently missed — always interrogate the SVC–RA junction from the subcostal bicaval view and look for anomalous right pulmonary veins draining to the SVC.
Qp:Qs >1.5 with RV dilation is the standard threshold for closure — below this, haemodynamic benefit is uncertain.
CHD Defects
15 major congenital defects