What does a split S2 (second heart sound) indicate and how is it managed?

Split S2: Clinical Significance and Management

A split S2 (second heart sound) is a normal physiological finding that reflects the asynchronous closure of the aortic and pulmonic valves, and importantly, a normally split S2 is a reliable physical examination finding that excludes the possibility of severe aortic stenosis. 1

Understanding Split S2

• The second heart sound (S2) consists of two components: A2 (aortic valve closure) and P2 (pulmonic valve closure), with the aortic valve typically closing before the pulmonic valve, creating a time delay known as the "split" 2
• Normal physiological splitting varies with respiration - the split widens during inspiration and narrows during expiration 2, 3
• The normal split duration is typically less than or equal to 45 milliseconds (0.045 seconds) 4, 5

Types of S2 Splitting and Clinical Significance

Normal Physiological Split

• Varies with respiration (widens during inspiration, narrows during expiration) 2
• Reflects normal hemodynamics between the left and right sides of the heart 2, 5

Fixed Split

• Split remains constant throughout the respiratory cycle 2
• Associated with atrial septal defect (ASD) and pulmonary stenosis (PS) 2, 6
• Does not vary with respiration as would be expected in normal physiology 2

Wide Split

• Split duration exceeds 60 milliseconds (0.06 seconds) 4, 6
• May be seen in right bundle branch block (RBBB), though not consistently 4
• Can be detected using advanced signal processing techniques such as wavelet transform 6

Paradoxical (Reversed) Split

• P2 occurs before A2 (reverse of normal order) 3
• Single sound during inspiration, split during expiration (opposite of normal pattern) 3
• Associated with:
  • Aortic stenosis
  • Left ventricular volume overload
  • Left ventricular conduction defects
  • Left bundle branch block (LBBB) 3

Diagnostic Approach

• Echocardiography is the recommended first-line diagnostic test when evaluating abnormal heart sounds 7
• Transthoracic echocardiography is specifically recommended for:
  • Initial diagnosis and assessment of suspected valvular disease 1
  • Assessment of left ventricular wall thickness, size, and function 1
  • Re-evaluation when symptoms or signs change 1

Clinical Importance in Valvular Disease

• A normally split S2 reliably excludes severe aortic stenosis - this is a key physical examination finding with high specificity 1
• In severe aortic stenosis, S2 is typically single or paradoxically split 1
• Other classic findings of severe aortic stenosis include:
  • Loud (grade 4/6), late-peaking systolic murmur radiating to the carotids
  • Delayed and diminished carotid upstroke (though this may be normal in elderly patients) 1

Management Recommendations

• For asymptomatic patients with suspected valvular disease, follow-up echocardiography is recommended at different intervals based on severity 1:

  • Severe aortic stenosis: yearly
  • Moderate aortic stenosis: every 1-2 years
  • Mild aortic stenosis: every 3-5 years 1

• Exercise testing:

  • May be considered in asymptomatic patients with aortic stenosis to elicit exercise-induced symptoms and abnormal blood pressure responses (Class IIb recommendation) 1
  • Should NOT be performed in symptomatic patients with aortic stenosis (Class III recommendation) 1

Special Considerations

• During pregnancy, the increased blood volume and enhanced cardiac output can accentuate murmurs associated with stenotic heart valve lesions 1
• A soft grade 1-2 midsystolic murmur along the mid to upper left sternal edge is a frequent normal finding during pregnancy 1
• The second heart sound may widen and appear fixed during later stages of pregnancy 1

Common Pitfalls

• Mistaking a normal split S2 for pathology - remember that physiological splitting varies with respiration 2
• Failing to recognize that a normally split S2 excludes severe aortic stenosis 1
• Not appreciating that split S2 characteristics can change with aging and other physiological states 1, 4
• Overlooking that in elderly patients, carotid upstroke may be normal despite severe aortic stenosis due to vascular aging 1