How to clinically determine a narrow or wide split of S2?

Clinical Determination of Narrow vs. Wide Split of S2

The split of S2 is clinically determined by auscultating at the left upper sternal border during both inspiration and expiration, with a normal physiological split widening during inspiration and narrowing during expiration, while a wide split persists during expiration and a narrow split may be difficult to appreciate even during inspiration. 1

Anatomy and Physiology of S2 Split

S2 consists of two components:

• A2 (Aortic component): Occurs first, from aortic valve closure
• P2 (Pulmonic component): Occurs second, from pulmonic valve closure

The time interval between these components is called the "split" of S2.

Auscultation Technique

1. Position: Have patient in seated or supine position
2. Stethoscope placement: Left upper sternal border (2nd-3rd intercostal space)
3. Respiratory maneuver: Ask patient to breathe normally, then take a deep breath and hold

Types of S2 Splits and Their Clinical Identification

1. Normal Physiological Split

• Characteristics: Split widens during inspiration (5-30 ms) and narrows or disappears during expiration
• Mechanism: During inspiration, increased venous return to right heart delays pulmonic valve closure
• Auscultation finding: Two distinct components heard during inspiration, single sound during expiration

2. Wide Split

• Characteristics: Split remains wide (>40 ms) during both inspiration and expiration
• Mechanism: Delayed right ventricular activation or prolonged right ventricular ejection
• Auscultation finding: Two clearly separated components heard during both inspiration and expiration
• Common causes: Right bundle branch block, pulmonic stenosis 1

3. Fixed Split

• Characteristics: Split remains constant throughout respiratory cycle
• Mechanism: Right ventricular volume overload prevents normal respiratory variation
• Auscultation finding: Two components with equal separation during both inspiration and expiration
• Pathognomonic for: Atrial septal defect 1, 2

4. Paradoxical Split

• Characteristics: Split narrows during inspiration and widens during expiration (opposite of normal)
• Mechanism: Delayed left ventricular activation or prolonged left ventricular ejection
• Auscultation finding: Split heard during expiration, single sound during inspiration
• Common causes: Left bundle branch block, severe aortic stenosis 1

5. Narrow Split

• Characteristics: Components are closely spaced (<20 ms) even during inspiration
• Mechanism: Early pulmonic valve closure or delayed aortic valve closure
• Auscultation finding: May sound like a single S2 even during inspiration
• Common causes: Pulmonary hypertension, aortic stenosis with delayed A2

Clinical Pearls for Accurate Assessment

1. Use the diaphragm of the stethoscope for high-frequency S2 components
2. Have patient breathe slowly to clearly appreciate respiratory variation
3. Listen during held inspiration to maximize the split in normal hearts
4. Compare with expiration to determine if the split narrows appropriately
5. Use maneuvers like Valsalva to help distinguish heart sounds 1

Common Pitfalls to Avoid

1. Mistaking S1 for S2: Remember S2 is typically louder at the base of the heart
2. Missing a paradoxical split: Always listen through complete respiratory cycles
3. Overlooking a single S2: In severe aortic stenosis, A2 may be inaudible, giving the false impression of a single S2 1
4. Confusing tachycardia-induced summation gallops with splits: Slow the heart rate if needed

Advanced Assessment

For more precise measurement of S2 splits, phonocardiography or echocardiography may be used, but clinical auscultation remains the frontline diagnostic approach 3, 4.