Why does splitting if S heart sound occurs with atrial septal defect but not ventricular septal defect?

Atrial septal defect (ASD) is a condition characterized by a hole between the upper chambers of the heart. This abnormality allows blood to flow directly from the left atrium to the right atrium, which bypasses going through pulmonary circulation and therefore puts extra strain on the right side of the heart. The additional blood in this chamber of the heart can cause an extra sound known as splitting of S2 Heart Sound.

On the other hand, Ventricular septal defect (VSD) is a condition where there’s an opening between two lower chambers of your heart – left and right ventricles which allows oxygen-rich blood from your left ventricle to mix with oxygen-poor blood from your right ventricle. This mixing produces enough volume or pressure in either chamber that any variation in inflow like splitting will not be heard because it will be muffled by presence of combined sounds due to both sides. So, for VSDs spitting does not occur as compared with ASD cases because there's no increase or decrease in flow through either side creating a distinct sound difference that is missing when you have mixed flow in VSD anomaly case

Furthermore, normal S2 Heart Sound occurs during diastole and it’s caused by closing valves such as tricuspid valve along with mitral valve oscillating back and forth due to pressure gradient while squeezing out residual volume in their respective chambers. On other hand Splitting occurs if there’s sufficient change in intracardiac pressures across those valves so that one half opens faster than other resulting into two individual sounds produced thus splitting up Sounds 2 into two components instead of one single component momentary occlusion created during closure sound occurring together producing single merged sound instead separate individual components; this happens mainly when patients have mitral insufficiency making early diastolic opening more prominent causing higher intensity split earlier than expected giving rise to audible Splitting occurring shortly after respiratory cycle ending giving rise typical pattern we observe doing physical exam on affected patients having ASD conditions but not present if patient has VSD since those cusps force exerted via high filling pressure which creates same speed mechanical forces on both sides yielding unfavorably no difference leading towards single S2 sound without any extra splits , hope this helps understanding Split SV?—?S2 mechanism better!