ASD

Definition & Epidemiology

Type	Prevalence	Anatomical Location	Key Morphological Features
Ostium Secundum	80%	Central portion (Fossa ovalis)	Incomplete formation or fenestration of primary atrial septum.
Ostium Primum	10%	Lower atrial septum	Part of atrioventricular septal defect (AVSD) spectrum. Inferior margin formed by AV valve. Associated cleft in left AV valve.
Sinus Venosus	10%	Junction of SVC/IVC and RA	Straddles defect. Lacks superior margin. Highly associated with anomalous right pulmonary venous drainage.
Coronary Sinus	Rare	Coronary sinus	Unroofed coronary sinus producing communication between coronary sinus and left atrium.
Vestibular	Rare	Antero-inferior rim	True septal deficiency within antero-inferior muscular rim of oval fossa.

Physiology follows pre-tricuspid shunt.
Left-to-right shunt dictated by lower right atrial (RA) pressure and relative higher compliance of right ventricle (RV) compared to left ventricle (LV).
Shunting occurs predominantly during late ventricular systole and early diastole; increases during atrial contraction and expiration.
Significant shunt defined as pulmonary-to-systemic blood flow ratio (Qp:Qs) > 1.5:1.
Induces volume overload of RA, RV, and main pulmonary artery (PA) dilation.
Pulmonary arterial pressures initially normal.
Chronic volume overload triggers pulmonary vascular bed remodeling (myo-intimal cell proliferation, medial smooth muscle increase) leading to pulmonary arterial hypertension (PAH).

Syndrome / Genetic Variant	Key Clinical Features & Associations
Holt-Oram Syndrome	Autosomal dominant TBX5 mutation. Upper limb/radial defects, phocomelia, AV block, secundum ASD.
NKX2.5 Mutation	Familial ASD associated with progressive atrioventricular conduction block.
GATA4 Mutation	Familial secundum ASD without associated heart block.
Ellis-van Creveld	Autosomal recessive EVC mutation. Common atrium/ASD, short limbs/ribs, postaxial polydactyly, dysplastic nails.

Infancy: Mostly asymptomatic; routinely discovered during general physical examination.
Symptoms rare in childhood, manifest 3rd to 5th decade of life.
Older patients: Fatigue, dyspnea, effort intolerance, recurrent respiratory infections, palpitations.
Right-sided heart failure, peripheral edema, syncope develop late.
Auscultation Findings:
- Grade 2-3/6 flow-related ejection systolic murmur at left upper sternal border (caused by increased flow across normal pulmonary valve).
- S2: Widely split and fixed during all respiratory phases (due to prolonged RV ejection time and increased pulmonary capacitance/"hang-out" interval).
- Mid-diastolic rumbling murmur at lower left sternal border (flow across tricuspid valve; indicates massive shunt Qp:Qs > 2:1).
Palpation: Hyperdynamic precordium, left parasternal RV lift/heave.

Right axis deviation, right ventricular hypertrophy.
Incomplete right bundle branch block (rSR' pattern in V1) seen in ~90% cases.
Crochetage sign: Notch near apex of R wave in inferior limb leads (II, III, aVF). Highly specific for ASD when combined with incomplete RBBB.
Left axis deviation (-30° to -90°) pathognomonic for ostium primum ASD.
Prolonged PR interval common (prolonged interatrial conduction time).

Mild-to-moderate cardiomegaly.
RA and RV enlargement (best appreciated on lateral view).
Prominent main PA segment, plethoric lung fields (increased pulmonary vascularity).
LA normal size (enlargement suggests associated mitral regurgitation).
Late cases with PAH show massive central PA dilation with peripheral pruning.

Confirms diagnosis, calculates Qp:Qs, evaluates anatomic rims, excludes anomalous venous connections.
Transthoracic Echocardiography (TTE): Subcostal, apical 4-chamber, and parasternal short-axis views ideal for assessing defect dimensions.
RV volume overload signs: Diastolic septal flattening, paradoxical/anterior systolic ventricular septal motion.
T-artifact: Brightening at defect edge due to increased ultrasound reflectivity at tissue-blood interface.
Transesophageal Echocardiography (TEE): Essential for complex shunts (sinus venosus, coronary sinus) and periprocedural guidance during transcatheter closure.

Cardiac Magnetic Resonance (CMR): Quantifies Qp:Qs, precise RV/LV volume assessment, invaluable for delineating anomalous pulmonary venous drainage.
Cardiac Catheterization: Seldom diagnostic. Reserved for assessing severe PAH, testing vasoreactivity, or calculating pulmonary vascular resistance (PVR) prior to closure.

Spontaneous Closure: High likelihood for defects <5mm; mostly occurs by age 3 years. Defects >8mm unlikely to close.
Arrhythmias: Atrial flutter and fibrillation prevalence increases significantly after age 40 or with co-existing PAH.
Pulmonary Arterial Hypertension (PAH): Develops in small proportion (6-17%). Unpredictable, progressive. Can lead to irreversible Eisenmenger syndrome (cyanosis, shunt reversal).
Paradoxical Embolism: Risk of venous thromboembolism traversing defect leading to stroke.
Infective Endocarditis: Extremely rare due to low-velocity turbulence. Antibiotic prophylaxis not routinely recommended.

Indications for Closure	Contraindications for Closure
Right heart volume overload / RV enlargement.	Severe, irreversible PAH.
Qp:Qs > 1.5:1 without cyanosis at rest.	PVR > 2/3 Systemic Vascular Resistance (SVR).
History or high risk of paradoxical embolism/stroke.	PA systolic pressure > 2/3 systemic systolic pressure.
Orthodeoxia-platypnea syndrome.	Net right-to-left shunting (Eisenmenger syndrome).

Preferred modality for secundum ASDs.
Pre-requisites: Adequate tissue rims (>5mm) away from SVC, IVC, AV valves, coronary sinus, and pulmonary veins.
Contraindications: Absent posterior-inferior rim (IVC margin) risks device embolization. Ostium primum, sinus venosus, and coronary sinus defects structurally unsuitable for devices.

Indications: Large defects, deficient rims, sinus venosus ASD, coronary sinus ASD, primum ASD, or concurrent surgical indications.
Procedure: Performed via median sternotomy or mini-sternotomy on cardiopulmonary bypass.
Technique: Primary direct suture (small defects) or patch closure using autologous pericardium, PTFE, or Dacron.
Specialized Procedures:
- Warden Procedure: Specifically for superior sinus venosus ASD with partial anomalous pulmonary venous return. Divides SVC above anomalous veins, anastomoses proximal SVC to RA appendage, and baffles remaining SVC stump (with pulmonary veins) through ASD into LA. Avoids sinus node injury.
- Transcaval Repair: Single autologous pericardial patch utilized for favorable sinus venosus anatomy; closes ASD while simultaneously rerouting pulmonary veins to LA.