LVOT obstruction causes the aortic valve to do what during systole?

In cases of left ventricular outflow tract (LVOT) obstruction, the aortic valve is influenced by the dynamics of flow and pressure changes in the left ventricle during systole. When there is an obstruction in the LVOT, the left ventricle experiences difficulty in ejecting blood into the aorta. This can lead to an increased pressure gradient across the aortic valve.

As the left ventricle contracts, the pressure may become so elevated that the aortic valve does not fully open or may even start to close while the ventricle is still in systole. This can occur because the valve leaflets may encounter altered flow dynamics, particularly in conditions like hypertrophic cardiomyopathy, where there is an obstruction caused by a thickened interventricular septum that limits the ability of the valve to open fully.

Additionally, if the obstruction situation is severe, the aortic valve may be forced to close prematurely due to the back pressure from the aorta, creating conditions where the valve cannot remain fully open through the entirety of systole. Thus, the phenomenon of closing during systole is due to the adverse effects of the obstruction impacting the normal functioning of the aortic valve during the heart's contraction phase.