What is the definition of a narrow split A2 (aortic valve component of the second heart sound) P2 (pulmonary valve component of the second heart sound) and a wide split A2 P2?

Heart Sound Auscultation: Understanding A2-P2 Splitting

The normal second heart sound (S2) consists of aortic valve closure (A2) followed by pulmonic valve closure (P2), with a narrow split of approximately 30 milliseconds during expiration that widens to about 50-60 milliseconds during inspiration. This physiological splitting pattern is a key finding in normal cardiac auscultation 1.

Physiological Mechanisms of S2 Splitting

The second heart sound (S2) consists of two components:

• A2: Aortic valve closure component (occurs first)
• P2: Pulmonary valve closure component (occurs second)

Normal Splitting Pattern

• Narrow split: During expiration, A2 and P2 are separated by approximately 30 milliseconds
• Widened split: During inspiration, the split increases to about 50-60 milliseconds
• Mechanism: Inspiratory widening occurs primarily due to:
  • Decreased pulmonary vascular impedance (approximately 40% of the effect) 2
  • Prolongation of right ventricular systole (approximately 30% of the effect) 2
  • Shortening of left ventricular systole (approximately 30% of the effect) 2

Abnormal Splitting Patterns

Wide (Persistent) Split

• Definition: A2-P2 interval exceeds 60 milliseconds during expiration and widens further during inspiration
• Key causes:
  • Pulmonic stenosis (delayed P2 due to right ventricular outflow obstruction) 1
  • Right bundle branch block (delayed right ventricular activation)
  • Volume overload of right ventricle

Fixed Split

• Definition: A2-P2 interval remains constant (does not change) during respiration
• Key cause: Atrial septal defect (ASD) 3, 1
• Clinical presentation: Often accompanied by a pulmonic flow murmur and fixed splitting of S2 3

Narrow (Physiological) Split

• Definition: Normal separation between A2 and P2 that widens with inspiration
• Clinical significance: Expected finding in healthy individuals

Paradoxical Split

• Definition: P2 occurs before A2, causing the split to narrow or disappear during inspiration
• Key causes:
  • Left bundle branch block (most common) 1
  • Severe aortic stenosis 1
  • Hypertrophic cardiomyopathy

Clinical Assessment of S2 Splitting

Auscultation Technique

• Best heard at the second left intercostal space (pulmonic area)
• Patient should be in sitting position, leaning forward slightly
• Ask patient to breathe normally, then hold breath after deep inspiration and expiration to assess respiratory variation

Distinguishing Features

• Normal split: Widens during inspiration, narrows during expiration
• Wide split: Excessively wide during expiration, widens further with inspiration
• Fixed split: No change in width between inspiration and expiration
• Single S2: Components may be fused or one component may be inaudible
• Paradoxical split: Components separate during expiration and fuse during inspiration

Clinical Pearls and Pitfalls

• In patients with pulmonary hypertension, P2 becomes louder and may be heard at the apex 3
• Fixed splitting of S2 is a classic finding in ASD and should prompt further evaluation with echocardiography 3
• A loud P2 component suggests pulmonary hypertension 3
• Absence of normal splitting makes severe aortic stenosis unlikely 1
• Respiratory maneuvers are essential to properly assess splitting patterns 1

Diagnostic Implications

Recognizing abnormal splitting patterns helps identify:

• Congenital heart defects (especially ASD)
• Valvular abnormalities (pulmonic or aortic stenosis)
• Conduction abnormalities (bundle branch blocks)
• Pulmonary hypertension
• Ventricular dysfunction

Echocardiography remains the gold standard for confirming the underlying cause of abnormal S2 splitting patterns 1.