A fixed split S2 heart sound is indicative of which condition?

• A. Atrial septal defect
• B. Ventricular septal defect
• C. Mitral valve prolapse
• D. Heart failure

Answer: (A)

A fixed split S2 heart sound is most commonly associated with atrial septal defect (ASD). This condition leads to left-to-right shunting of blood due to the presence of an abnormal opening in the atrial septum. Because of this shunting, there is increased blood flow into the right atrium and subsequently into the right ventricle and pulmonary arteries.

When blood flow is increased to the right side of the heart, especially during the inspiration phase of the respiratory cycle, the closure of the pulmonic valve occurs later than that of the aortic valve. In a normal situation, the S2 sound can split during inspiration and then return to a unified sound during expiration. However, in the case of a fixed split S2, the splitting does not vary with respiration, and this is primarily due to the increased blood flow and pressure in the right heart, leading to persistent delay in the closure of the pulmonic valve.

Conditions like ventricular septal defect, mitral valve prolapse, or heart failure do not typically produce a fixed split of the S2 heart sound, making ASD the most accurate answer in this scenario. In these conditions, the splitting of the heart sounds may behave differently, often correlating with various phases of