Why there is wide variable split S2 in VSD ? Just tell me why variable?

Why there is wide variable split S2 in VSD ? Just tell me why variable ?

A wide and variable split of the second heart sound (S2) can occur in cases of ventricular septal defect (VSD) due to the timing of the closure of the aortic and pulmonary valves.

In a normal cardiac cycle, the aortic valve closes slightly before the pulmonary valve during the second heart sound (S2). This results in a physiological split S2, where the “A2” component corresponds to aortic valve closure, and the “P2” component corresponds to pulmonary valve closure. The brief time interval between the closure of these two valves creates the normal physiological split S2.

In the context of a VSD, the wide variability in the timing of the split S2 occurs because the VSD allows blood to flow between the left ventricle (which pumps blood through the aortic valve) and the right ventricle (which pumps blood through the pulmonary valve) during ventricular systole (the phase when the ventricles contract).

Depending on the size of the VSD, the amount of blood shunting between the ventricles, and the pressure differences between them, the timing of the closure of the aortic and pulmonary valves can be affected. This can lead to variable splits of S2. Here’s how it works:

  1. Small VSD: In cases of a small VSD, the pressure differences between the left and right ventricles may not be significant, and the aortic and pulmonary valves may close relatively synchronously, resulting in a minimal or narrow split S2.
  2. Large VSD: In contrast, a large VSD allows for more significant blood flow between the ventricles, leading to greater pressure differences. This can cause the aortic and pulmonary valves to close at different times, resulting in a wider split S2.
  3. Variable Split: The variability in the size and characteristics of VSDs among individuals can lead to variable splitting of S2. Additionally, factors such as heart rate, volume status, and cardiac contractility can influence the timing and degree of split S2 in VSD.

The variability in the split S2 can be a diagnostic clue for healthcare providers evaluating patients with suspected VSD. Echocardiography is typically used to confirm the presence of a VSD, assess its size and location, and determine the associated hemodynamic effects. The specific characteristics of the split S2 can provide valuable information to guide clinical evaluation and management decisions.