Under what circumstances is split S2 typically heard?

Split S2 is typically heard during specific physiological or pathophysiological conditions related to the timing of cardiac events, particularly concerning the closure of the aortic and pulmonic valves. When considering atrial septal defect or atrioventricular delay, the incidence of split S2 makes sense due to the prolonged right ventricular systole in these conditions.

In an atrial septal defect, the increased blood flow in the right atrium leads to an increased volume of blood delivered to the right ventricle, which can delay the closure of the pulmonic valve relative to the aortic valve. This delay results in a more pronounced splitting of the second heart sound during inspiration, when right ventricular filling is enhanced. Moreover, in cases of atrioventricular delay, the abnormal conduction through the AV node can also alter the timing between the closure of the aortic and pulmonic valves, leading to a similar effect.

In contrast, the other options do not typically lead to a split S2. Ventricular fibrillation is a life-threatening arrhythmia characterized by disorganized electrical activity in the ventricles and would not normally produce discernible heart sounds. Mitral regurgitation generally leads to a single S1 sound and does not affect the