second (2nd) heart sound (reversed split)

Last reviewed 01/2023

In this condition, P2 occurs before A2.

On expiration, A2 is delayed such that it occurs after P2. Inspiration causes P2 to be delayed and the split is diminished.

Possible causes of a delayed A2 include:

• electrical delay - left bundle branch block
• systolic hypertension
• severe aortic stenosis or HOCM
• patent ductus arteriosus
• left heart failure

In patients with aortic stenosis, A2 is often very soft or even absent, in such circumstances there appears to be a single component to the second heart sound.

Note that an early P2 may occur in type B Wolff-Parkinson- White syndrome (1).

Reference:

• Braunwald E. Heart Disease - A Textbook of Cardiovascular Medicine,WB Saunders.