MioAtlas
G4: Congenital heart disease

Ostium secundum atrial septal defect

Congenital defect of the interatrial septum located in the region of the fossa ovalis (ostium secundum), resulting from excessive resorption of the septum primum or deficient development of the septum secundum.

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Definition

Congenital defect of the interatrial septum located in the region of the fossa ovalis (ostium secundum), resulting from excessive resorption of the septum primum or deficient development of the septum secundum. It causes a left-to-right shunt that produces chronic volume and diastolic overload of the right atrium, right ventricle, and pulmonary circulation [C5] [G4-04].

Severity criteria

  • Mild (L): Small shunt with Qp:Qs ratio < 1.5 without right ventricular volume overload (normal right ventricular dimensions) [C4] [C5].
  • Moderate (M): Significant shunt with Qp:Qs ratio ≥ 1.5 and echocardiographic signs of right ventricular volume overload (dilation of right-sided chambers) [C4] [C5].
  • Severe (G): Significant shunt with Qp:Qs ratio ≥ 1.5, distinguished qualitatively from the moderate form by the presence of severe volumetric overload of the right ventricle, marked dilation of right-sided chambers, and appearance of a functional tricuspid mid-diastolic flow rumble due to hyperafflux [C4] [C5] [G4-04].

Findings by layer

Hemodynamics

  • Pulmonary-to-systemic flow ratio: L < 1.5 (without overload); M and G ≥ 1.5 (with RV volume overload) [C4] [C5].
  • Shunt direction: Left-to-right at atrial level [C5] [G4-04].
  • Pulmonary artery pressure (systolic pulmonary artery pressure, mean pulmonary artery pressure): Normal in mild forms; possible elevation in the presence of substantial hyperflow [C5].

Rhythm

  • Normal sinus rhythm habitual [C5].
  • Atrial fibrillation or atrial flutter in adults due to chronic right atrial remodeling and dilation [C4] [C5].

ECG

  • Incomplete right bundle branch block (incomplete right bundle branch block, rsR' or rSr' pattern in V1) due to RV diastolic overload [E2] [G4-04].
  • Rightward QRS axis (right axis deviation) [E1] [G4-04].

Heart sounds and murmurs

  • Second heart sound (S2): Wide and fixed splitting of S2 (S2 split fixed), unvarying with respiration, pathognomonic of atrial septal defect [G1-11] [G4-04].
  • Systolic murmur: Soft ejection midsystolic murmur (grade 2–3/6) in pulmonary area due to hyperafflux across the normal pulmonary valve [G1-14] [G4-04].
  • Tricuspid rumble: In severe form (G), soft mid-diastolic rumble in tricuspid area (lower left sternal border) due to relative tricuspid stenosis from high-volume flow [G1-15] [G4-04].

Arterial pulse

  • Normal carotid and peripheral pulse [B4].

Jugular venous pulse

  • Normal or mildly elevated jugular venous pressure with prominent and equalized a and v waves in the presence of RV overload [B3].

Maneuvers

  • Respiration: S2 splitting interval remains fixed between inspiration and expiration [G1-11] [G4-04].
  • Valsalva maneuver: Decreases pulmonary ejection murmur intensity during strain phase [B1].

Simulator severity grades

Simulator severity grades: Mild, Moderate, Severe
Baseline rhythm: Normal Sinus Rhythm

Also known as: Ostium secundum atrial septal defect · Secundum atrial septal defect · Secundum ASD · Ostium secundum ASD

Other pathologies in this group

Related clinical comparisons

Sources

  1. [B1] Bedside diagnosis of systolic murmurs . N Engl J Med (1988) . DOI: 10.1056/NEJM198806163182404 PubMed: 2897627
  2. [B3] The jugular venous pressure revisited . Cleve Clin J Med (2013) . DOI: 10.3949/ccjm.80a.13039 PubMed: 24085809
  3. [B4] The Carotid Pulse . Clinical Methods: The History, Physical, and Laboratory Examinations (1990) . PubMed: 21250154
  4. [C4] 2025 ACC/AHA/HRS/ISACHD/SCAI Guideline for the Management of Adults With Congenital Heart Disease: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines . Circulation (2026) . DOI: 10.1161/CIR.0000000000001402 PubMed: 41411375
  5. [C5] 2020 ESC Guidelines for the management of adult congenital heart disease . Eur Heart J (2021) . DOI: 10.1093/eurheartj/ehaa554 PubMed: 32860028
  6. [E1] AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part V: electrocardiogram changes associated with cardiac chamber hypertrophy: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: endorsed by the International Society for Computerized Electrocardiology . Circulation (2009) . DOI: 10.1161/CIRCULATIONAHA.108.191097 PubMed: 19228820
  7. [E2] AHA/ACCF/HRS recommendations for the standardization and interpretation of the electrocardiogram: part III: intraventricular conduction disturbances: a scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society: endorsed by the International Society for Computerized Electrocardiology . Circulation (2009) . DOI: 10.1161/CIRCULATIONAHA.108.191095 PubMed: 19228822
  8. [G1-11] The Second Heart Sound . Clinical Methods: The History, Physical, and Laboratory Examinations (1990) . PubMed: 21250183
  9. [G1-14] Systolic Murmurs . Clinical Methods: The History, Physical, and Laboratory Examinations (1990) . PubMed: 21250186
  10. [G1-15] Diastolic Murmurs . Clinical Methods: The History, Physical, and Laboratory Examinations (1990) . PubMed: 21250187
  11. [G4-04] Atrial septal defects . Lancet (2014) . DOI: 10.1016/S0140-6736(13)62145-5 PubMed: 24725467