Can S2 splitting be heard in all auscultation areas in a 20-year-old male patient with an atrial septal defect (ASD) and a recent history of upper respiratory infection?

S2 Splitting in Atrial Septal Defect: Auscultation Location

Fixed splitting of the second heart sound (S2) in ASD is classically heard best at the pulmonic area (second left intercostal space) and left sternal border, but it is NOT reliably audible in all auscultation areas. 1

Where S2 Splitting is Best Heard

The characteristic fixed splitting of S2 in ASD is most audible at:

• Pulmonic area (second left intercostal space at the left sternal border) 1, 2
• Left sternal border (where right-sided heart sounds are best appreciated) 1

The systolic pulmonary flow murmur that accompanies ASD is also heard in these same locations. 1

Important Clinical Caveats

Fixed Splitting is Not Always Present

Fixed splitting of S2 is NOT invariable in ASD, even when hemodynamically significant. 1 The ACC/AHA guidelines explicitly state that "fixed splitting is not invariable" in their clinical examination section. 1

• A documented case report demonstrated an adult with confirmed ostium secundum ASD (with significant left-to-right shunt and normal pulmonary pressures) who had variable splitting rather than fixed splitting on auscultation. 3
• The absence of wide and persistent S2 splitting does not exclude uncomplicated ASD in adults when other findings (ECG showing incomplete RBBB, chest X-ray showing increased pulmonary vascularity) suggest the diagnosis. 3

Why S2 Splitting Occurs in ASD

The pathophysiology explains the location specificity:

• The fixed split results from persistent right ventricular volume overload causing delayed pulmonic valve closure throughout the respiratory cycle. 1, 2
• The aortic component (A2) closes before the pulmonary component (P2), creating the split. 4
• This phenomenon is best appreciated where P2 is loudest—at the pulmonic area and left sternal border, not at the apex or other distant sites. 1

Additional Auscultatory Findings in ASD

Beyond S2 splitting, listen for:

• Diastolic tricuspid flow rumble at the lower left sternal border when the shunt is large (Qp:Qs >2.0), indicating significant volume overload. 1, 2
• Systolic ejection murmur (grade 2-3/6) at the pulmonic area from increased flow across the pulmonary valve. 1, 5

Clinical Context for Your Patient

In a 20-year-old male with ASD and recent upper respiratory infection:

• Focus auscultation at the pulmonic area and left sternal border for S2 splitting. 1
• The recent URI does not alter where S2 splitting is heard, though it may affect overall cardiac output and shunt dynamics. 1
• If S2 splitting is not clearly audible, this does not rule out hemodynamically significant ASD—proceed with echocardiography to assess RV volume overload, which is the definitive indicator of shunt significance. 1, 6