What is the physiological cause of effort intolerance in children with severe aortic stenosis?

Effort intolerance in children with severe aortic stenosis is primarily due to decreased cardiac output during physical exertion. Aortic stenosis is a condition where the aortic valve does not open fully, leading to a restriction of blood flow from the heart to the aorta and subsequently to the body. During physical activity, the heart requires an increased amount of blood flow to meet the metabolic demands of the muscles. However, in the presence of severe aortic stenosis, the heart struggles to pump sufficient blood because the narrowed valve creates an obstruction, resulting in reduced volume ejected from the heart.

As children engage in physical activities, their body demands more oxygen and nutrients, which would normally be supplied by an increase in cardiac output. However, the compromised ability of the heart to increase output leads to fatigue, weakness, and effort intolerance. Thus, the physiological cause of effort intolerance directly relates to the heart's inability to deliver adequate blood flow during exertion, which is significantly impacted by the severe narrowing of the aortic valve.

Increased heart rate during exertion, inadequate lung function, and elevated systemic blood pressure do not directly account for the specific mechanism behind effort intolerance in this context. The core issue remains the decreased cardiac output due to the mechanical obstruction