Learning Objectives

Understand the hemodynamic basis of the second heart sound (S2) and its components (A2 and P2). Differentiate between physiologic and pathological splitting patterns. Identify the clinical conditions associated with wide, fixed, and paradoxical splitting.

Physiologic Splitting

Normal splitting occurs during Inspiration because decreased intrathoracic pressure affects the right heart more significantly than the left.

• Mechanism: Inspiration → ↓ intrathoracic pressure → ↑ venous return → ↑ RV filling → ↑ RV stroke volume → ↑ RV ejection time.
• Result: This leads to a delayed closure of the pulmonic valve (P2) relative to the aortic valve (A2).
• Impedance: ↓ pulmonary impedance (due to ↑ the capacity of pulmonary circulation) during inspiration also contributes to the delayed P2.
• Expiration: The split disappears or is minimal as the RV ejection time shortens.

Wide Splitting

An exaggeration of normal splitting where the delay in RV emptying is present even during expiration.

• Clinical Causes: Conditions that delay RV emptying, such as Pulmonic Stenosis or Right Bundle Branch Block (RBBB).
• Auscultation: The P2 sound is delayed significantly; the split is audible during expiration and widens further during inspiration.

Fixed Splitting

The split is audible and constant, regardless of the phase of respiration.

• Classic Cause: Atrial Septal Defect (ASD).
• Mechanism: ASD → Left-to-Right shunt → chronic ↑ RA and RV volumes → ↑ flow through the pulmonic valve.
• Result: Pulmonic valve closure is permanently delayed, making the split independent of respiration.

Paradoxical Splitting

A reversal of the normal order; the aortic valve (A2) closes AFTER the pulmonic valve (P2).

• Clinical Causes: Conditions that significantly delay LV emptying, such as Aortic Stenosis or Left Bundle Branch Block (LBBB).
• Auscultation: On Inspiration, the normal delay of P2 moves it closer to the already delayed A2, eliminating the split.
• Expiration: The split is audible because P2 moves away from the delayed A2 (the opposite of physiologic splitting).

Activity