In a case of aortic stenosis, which characteristic change in the aortic valve is most commonly observed?

In aortic stenosis, the most commonly observed characteristic change in the aortic valve is fibrosis and calcification. This condition typically arises in older adults due to age-related degeneration of the aortic valve, which leads to the accumulation of calcium deposits. These changes stiffen the valve leaflets, reducing their ability to open properly during systole, which in turn causes the heart to work harder to pump blood through the narrowed opening.

Fibrosis contributes to the thickening of the valvular tissue, while calcification leads to further rigidity and narrowing. This process usually develops over many years and is a significant aspect of the pathophysiology of aortic stenosis, particularly in elderly patients who may have other contributing factors such as hypercholesterolemia or hypertension.

While other conditions mentioned, like myxomatous degeneration and congenital bicuspid valve, can lead to aortic stenosis, they are not the most common causes of the degenerative form seen in older patients. Infective endocarditis is an inflammatory condition that impacts the valve but is not a characteristic change of aortic stenosis. Therefore, fibrosis and calcification are definitive markers of aortic stenosis, representing the most prevalent alterations seen in the valve in these patients.