What is indicated by a wide split, fixed S2?

A wide split, fixed S2 is a hallmark characteristic often associated with an atrial septal defect (ASD). In this condition, there is an abnormal connection between the left and right atria, which allows for increased blood flow from the left atrium to the right atrium. This causes delayed closure of the pulmonic valve due to prolonged right ventricular systole, leading to a wide split of the second heart sound (S2) that does not vary with respiration, hence its designation as "fixed."

The "fixed" aspect means that during both inhalation and exhalation, the split does not change, which differentiates it from other conditions that may cause a split S2 that varies with breathing. This is a key diagnostic indicator in recognizing ASD, making it essential in clinical assessment.

In contrast, conditions such as aortic stenosis or left bundle branch block can also influence heart sounds but do not typically result in a wide, fixed split S2. Mitral regurgitation may cause a different type of sound due to the alteration in hemodynamics and does not usually present with a fixed split S2. Understanding these specific details helps in identifying ASD and differentiating it from other cardiac conditions.