Atrial Septal Defect
Cardiology
Illness script · Cardiology
Atrial Septal Defect
Congenital opening in the interatrial septum causing left-to-right shunting, right heart volume overload, and increased pulmonary blood flow.
This illness script for Atrial Septal Defect covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Most common congenital heart defect presenting in adults
- Female > Male (~2:1)
- Ostium secundum type most common (~70%, mid-septum)
- Ostium primum type (~20%) associated with Down syndrome and AV canal defects
- Sinus venosus type associated with anomalous pulmonary venous return
- Risk factors: maternal rubella, alcohol, advanced maternal age
02
Presentation
- Often asymptomatic through childhood; symptoms emerge in 3rd–4th decade
- Fixed, widely split S2 — the hallmark finding (splitting unchanged with respiration)
- Systolic ejection murmur at LUSB (high flow across pulmonic valve)
- Mid-diastolic rumble at LLSB if large shunt (increased tricuspid flow)
- Exertional dyspnea, fatigue, palpitations (atrial arrhythmias) in adults
- Paradoxical embolism → cryptogenic stroke (right-to-left embolic passage)
03
Pathophysiology
- LA pressure > RA pressure → left-to-right shunting at atrial level
- Right heart volume overload → RV dilation and increased pulmonary blood flow
- Chronic overcirculation → pulmonary hypertension over decades
- Pulmonary HTN can reverse shunt (right-to-left) → Eisenmenger syndrome
04
Diagnostics
- Transthoracic echo (TTE): first-line — shows RV dilation and shunt flow
- TEE or bubble study: gold standard for anatomy and shunt characterization
- EKG: incomplete RBBB ± right axis deviation (secundum); left axis deviation (primum)
- CXR: cardiomegaly, enlarged pulmonary arteries, increased pulmonary vascular markings
- Cardiac cath: step-up in O₂ saturation at RA level; Qp:Qs quantifies shunt size
05
Management
- Small secundum ASDs may close spontaneously before age 3
- Closure indicated when Qp:Qs ≥ 1.5:1 or right heart volume overload present
- Percutaneous catheter-based device closure: preferred for secundum ASDs
- Surgical repair required for primum and sinus venosus types
- Contraindicated if Eisenmenger syndrome established (irreversible pulmonary HTN)
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Ventricular Septal Defect
VSD produces a harsh holosystolic murmur at LLSB; ASD has a fixed split S2 with ejection murmur at LUSB.
Pulmonary Stenosis
PS also causes LUSB murmur but S2 is variably split with a soft, delayed P2; no fixed splitting.
Patent Ductus Arteriosus
PDA produces a continuous 'machinery' murmur heard best at the left infraclavicular area, not a split S2.
Innocent Flow Murmur
Innocent murmurs lack fixed S2 splitting and have a normal echo without right heart dilation.
Keep reading
Full library- Atrial FibrillationChaotic, disorganized atrial electrical activity causing irregularly irregular rhythm and loss of coordinated atrial contraction.
- Bacterial MeningitisAcute bacterial infection of the subarachnoid space causing meningeal inflammation, often rapidly fatal without treatment.
Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.