What causes aortic stenosis

What is Aortic Stenosis?

Aortic stenosis is a condition where the aortic valve of the heart becomes narrowed or blocked. The aortic valve is one of the four valves in the heart, responsible for controlling blood flow from the left ventricle (the heart's main pumping chamber) into the aorta, the body's largest artery. When the aortic valve doesn't open fully, it restricts blood flow to the rest of the body, forcing the heart to work harder to pump blood. Over time, this increased workload can lead to serious heart problems, including heart failure.

Primary Causes of Aortic Stenosis

The most frequent cause of aortic stenosis, particularly in older adults, is degenerative calcification. This is a process where calcium and cholesterol deposits build up on the leaflets (flaps) of the aortic valve. As these deposits accumulate, the valve leaflets become stiff, thick, and sometimes fused, preventing them from opening properly. This condition is often referred to as 'calcific aortic stenosis' or 'degenerative aortic valve disease'. While the exact trigger for this calcification isn't fully understood, it shares similarities with the hardening of arteries (atherosclerosis) and is associated with traditional cardiovascular risk factors.

Age-Related Calcification

As people age, their valves naturally undergo wear and tear. In many cases, this leads to the gradual accumulation of calcium on the aortic valve. This degenerative process is the most common reason for aortic stenosis in individuals over the age of 65. It's estimated that up to 25% of people in this age group have some degree of aortic valve calcification, though not all will develop significant stenosis requiring treatment.

Rheumatic Heart Disease

Another significant cause, especially in younger individuals or in regions where rheumatic fever is more prevalent, is rheumatic heart disease. Rheumatic fever is an inflammatory illness that can develop as a complication of untreated or inadequately treated streptococcal infections, such as strep throat or scarlet fever. The inflammation caused by rheumatic fever can damage the heart valves, including the aortic valve. This damage can lead to scarring, thickening, and distortion of the valve leaflets, which may eventually cause stenosis or regurgitation (leaking) of the valve. Rheumatic heart disease often affects multiple valves, but the aortic and mitral valves are most commonly involved.

Congenital Heart Defects

In some individuals, aortic stenosis is present from birth due to a congenital heart defect. The most common congenital abnormality affecting the aortic valve is a bicuspid aortic valve. Normally, the aortic valve has three leaflets. However, in people with a bicuspid aortic valve, there are only two leaflets. While many individuals with a bicuspid aortic valve live normal lives without symptoms, this structural abnormality makes the valve more prone to developing stenosis or regurgitation over time. It is estimated that 1-2% of the general population is born with a bicuspid aortic valve, and it is a significant cause of aortic stenosis in younger adults.

Risk Factors for Developing Aortic Stenosis

Several factors can increase an individual's risk of developing aortic stenosis:

• Age: The risk increases significantly with age, especially after 65.
• High Blood Pressure (Hypertension): Chronic high blood pressure can put extra strain on the aortic valve and contribute to its calcification.
• High Cholesterol: Similar to atherosclerosis, high cholesterol levels can contribute to the buildup of deposits on the valve.
• Chronic Kidney Disease: Patients with chronic kidney disease often have abnormal calcium and phosphate levels, which can promote valve calcification.
• Smoking: Smoking is a well-known risk factor for cardiovascular disease, including atherosclerosis, which can affect heart valves.
• Family History: A family history of aortic stenosis or bicuspid aortic valve may increase an individual's predisposition.
• Certain Medical Conditions: Conditions like Paget's disease of bone and previous radiation therapy to the chest can also be associated with aortic valve calcification.

Understanding the Progression

Aortic stenosis typically develops slowly over many years. In the early stages, the valve narrowing may be mild, and the heart can compensate. However, as the stenosis progresses, the heart has to work increasingly harder. This can lead to symptoms such as shortness of breath, chest pain or tightness, fatigue, dizziness, fainting spells, and palpitations. If left untreated, severe aortic stenosis can lead to heart failure and can be life-threatening.

Diagnosis usually involves a physical examination (listening for a heart murmur), an echocardiogram (ultrasound of the heart), and sometimes other imaging tests. Treatment options depend on the severity of the stenosis and the patient's overall health and may include medication to manage symptoms or, in moderate to severe cases, valve repair or replacement surgery.