Are S1 (first heart sound) and S2 (second heart sound) abnormal in patients with aortic stenosis?

Abnormal Heart Sounds in Aortic Stenosis

In aortic stenosis, the second heart sound (S2) is characteristically abnormal with a single or paradoxically split S2, while the first heart sound (S1) typically remains normal. 1

Abnormalities of S2 in Aortic Stenosis

• Aortic component (A2) abnormalities:

  • Soft or absent A2 due to reduced mobility of the calcified aortic valve 1, 2
  • This occurs because the calcified, stiffened valve cusps have reduced mobility and create less vibration upon closure

• Splitting pattern abnormalities:

  • Single S2 (most common finding in severe AS) due to inaudible A2 1
  • Paradoxical splitting (less common) where S2 splits during expiration and narrows or disappears during inspiration - the opposite of normal physiological splitting 2
  • The only physical examination finding that reliably excludes severe AS is a normally split S2 1

Pathophysiological Basis

• The abnormal S2 in aortic stenosis results from:

  • Reduced valve mobility due to calcification and fibrosis 3
  • Prolonged left ventricular ejection time causing delayed aortic valve closure 4
  • Influence of left ventricular pressure overload on interventricular septal function, affecting timing of both semilunar valves 4

• In severe AS, the prolonged left ventricular systole causes A2 to occur after P2, resulting in paradoxical splitting or a single S2 due to inaudible A2 2

Clinical Significance

• The presence of a single S2 or paradoxically split S2 is specific (though not sensitive) for severe AS 1
• These findings should be correlated with other classic physical examination findings of severe AS:
  • Loud (grade 4/6), late-peaking systolic ejection murmur radiating to the carotids
  • Delayed and diminished carotid upstroke (though this may be normal in elderly patients due to vascular aging) 1

Diagnostic Pitfalls

• In elderly patients, the classic physical findings may be altered:

  • The murmur may be softer or radiate to the apex
  • Carotid upstroke may appear normal due to vascular aging effects 1
  • The abnormal S2 may be difficult to appreciate in patients with tachycardia

• Echocardiography remains essential for confirming the diagnosis and severity of AS, but physical examination findings, particularly abnormal S2, provide important clinical context 1

Clinical Application

• When evaluating a patient with a systolic murmur, the finding of a single S2 or paradoxically split S2 should raise suspicion for severe AS
• The absence of these findings (i.e., normal physiologic splitting of S2) makes severe AS unlikely 1
• These auscultatory findings should be integrated with echocardiographic measurements to ensure accurate assessment of AS severity 1

Remember that while abnormal S2 is characteristic of AS, the first heart sound (S1) typically remains normal in isolated AS, which helps differentiate it from other valvular conditions.