Aortic Stenosis: Causes, Symptoms, Treatment, Prognosis, Pathophysiology
Among the many heart diseases, aortic stenosis is one of them. It is a heart condition where due to the narrowing of the aortic valve the heart is unable to pump out enough blood that is required. This makes the heart to work more which could eventually lead to heart failure. Aortic Stenosis is one of the chief reasons for sudden cardiac deaths.
Aortic Stenosis: Definition
The aorta, which is the main artery, transmits the blood from the heart to the body via the aortic valve. The aortic valve when narrows, intercepts the valve and obstructs the blood flow. This narrowing is called aortic stenosis.
When the aortic valve obstructs, the heart needs to put an extra effort in pumping blood to the body. This would eventually minimize the blood amount that is pumped out from the heart and may weaken the heart muscle.
A surgery is required to replace the aortic valve in severe cases; failing to do so may lead to heart problems.
Signs and Symptoms of Aortic Stenosis
The signs and symptoms of Aortic Stenosis include:
- Pain in the chest (Angina pectoris): Chest pain in aortic stenosis, is instigated by hard work and gets relieved with rest
- Palpitations: High heart beats, which can be felt
- Syncope: Weakness, fainting or dizziness with activity
- Heart failure: Dyspnea caused by exertion, Paroxysmal nocturnal dyspnea and orthopnea
- Cough: Possibly bloody
- Aortic stenosis could induce systolic hypertension. Although, severe aortic stenosis may barely increase the systolic blood pressure in patients
- The carotid arterial pulse may typically have decreased amplitude, delayed and high peak and a slow downslope, in critical aortic stenosis
- In a low percentage of the patients, the first symptom is sudden death, usually during arduous hard work
- The reason for sudden death is unidentified; however the inadequate blood flow in the coronary arteries and the abnormalities in the heart rhythm may be the reason.
In children and infants, symptoms of Aortic Stenosis include:
- Getting tired easily (in mild cases).
- Unable to gain weight.
- Serious breathing problems that would develop within few days of birth.
The mild or moderate aortic stenosis in children may get worse with age. There is a higher risk of bacterial endocarditis-a heart infection.
Causes of Aortic Stenosis
Aortic stenosis may be congenital, but generally it matures in later life. Children suffering from aortic stenosis may have other conditions since birth. Calcific aortic stenosis is a type of aortic stenosis that mainly occurs due to calcium deposits that narrow the valve. This happens to people who have abnormal aortic or bicuspid valves. Rarely, calcification develops if the patient has undergone chest radiation.
Rheumatic fever is one of the other causes which develop scarlet fever or strep throat. However, after a period of 5-10 years valve problems do not mature. In the US, rheumatic fever is becoming rarer. 2% of people over 65 years get aortic stenosis. It is more frequent in men than in women.
Pathophysiology of Aortic Stenosis
A systolic pressure gradient develops between the aorta and the left ventricle and resistance to systolic ejection occurs in aortic stenosis. The outflow obstruction caused, leads to an increase in systolic pressure in left ventricle (LV). The counteractive mechanism to normalize the stress on LV wall, parallel replication of sarcomeres increases LV wall thickness, producing concentric hypertrophy. However, the chamber is not dilated and the diastolic compliance is reduced. Eventually, LV end-diastolic pressure (LVEDP) rises, causing an increase in pulmonary capillary arterial pressures and a decrease in cardiac output. The contractility of the myocardium may diminish, leading to a decrease in cardiac output due to systolic dysfunction. This results in heart failure.
In many patients with aortic stenosis, cardiac output is maintained for many years and LV systolic function is conserved. The cardiac output may not increase during exercise, though it is normal at rest resulting in exercise-induced symptoms. Impaired LV relaxation or decreased LV compliance may lead to diastolic dysfunction.
In patients with severe aortic stenosis, the atrial contraction plays a vital role in diastolic filling of the left ventricle. This may lead to heart failure due to an inability to maintain cardiac output. Increased LV mass, increased LV systolic pressure and prolonged systolic ejection elevates the myocardial oxygen requirement, especially in the subendocardial region. The coronary blood flow is often reduced though it may be normal for LV mass.
Thus, myocardial perfusion is compromised by a relative shrink in myocardial capillary density and a diminished diastolic transmyocardial (coronary) perfusion gradient due to upraised LV diastolic pressure. Hence, the subendocardium is vulnerable to underperfusion, which results in myocardial ischemia.
Prognosis of Aortic Stenosis
Despite the presence of severe LV outflow tract obstruction (LVOTO), patients with severe aortic stenosis may show no symptoms for many years. Asymptomatic patients, even with critical aortic stenosis, have an excellent projection for survival, with an expected death rate of less than 1% per year. However, 4% of sudden cardiac deaths in asymptomatic patients with critical aortic stenosis occur. The amalgamated valve area and flow gradient patterns allow better characterization of clinical outcome among asymptomatic aortic stenosis patients.
Diagnosis of Aortic Stenosis
To diagnose aortic stenosis, the following tests can be undertaken:
- Electrocardiogram (ECG): Electrocardiogram is a tool that measures the heart's electrical activity.
- Chest X-ray: A normal heart shadow could be seen through chest X-ray.
- Echocardiography: Echocardiography is a tool that gets the detailed images depicting size and functioning of the heart including valves, chambers and connecting structures using ultrasound waves. It is a non-invasive tool that helps a doctor to diagnose aortic valve disease. Doppler, a technique that identifies the differential pressure on each sides of aortic valve can also be used.
- Cardiac catheterization: Cardiac catheterization is a significant tool in evaluating aortic stenosis. The aortic valve area is measured by calculating the rate of blood flow using a catheter.
- Exercise tests: In exercise tests, the patient exercises to increase the heart rate. The doctor evaluates the heart's response to exertion.
- Computerized tomography (CT) scan: CT scan is a tool that takes the images of the heart. The doctor can measure the size of aorta using this test.
- Magnetic resonance imaging (MRI): MRI uses powerful magnets and radio waves that take detailed images of the heart.
Treatment for Aortic Stenosis
Medications for Aortic Stenosis: Medications are ineffective to reverse aortic valve stenosis. However, a certain medications may help to get heart rate and heart rhythm in order.
Surgical Procedures for Aortic Stenosis: The patient with critical aortic stenosis may need aortic valve replacement or repair. Surgery is the primary treatment for Aortic Stenosis. The therapies to replace or repair aortic valve include:
- Balloon Valvuloplasty: Balloon valvuloplasty is a therapy that uses a soft, thin catheter tipped with a balloon to relieve aortic valve stenosis. It is effective in infants and children; in adults however the valve may narrow again.
- Aortic Valve Replacement: It is a primary surgical treatment performed during open-heart surgery to treat critical aortic stenosis.
- Transcatheter Aortic Valve Replacement (TAVR): Aortic valve replacement is a less invasive approach commonly used to treat critical aortic valve stenosis. It includes replacing the aortic valve with a prosthetic valve in the leg or the left ventricular apex.
- Surgical valvuloplasty: Surgical valvuloplasty is a less effective option in which the leaflets of the valve are fused together.
In addition, before any medical or dental procedure is carried out, antibiotics need to be administered post the aortic valve replacement surgery. This would reduce the risk of infection in the heart tissue (endocarditis).
Prevention of Aortic Stenosis:
The precautions that can prevent aortic valve stenosis are:
- Treating rheumatic fever.
- Treating the risk factors of coronary artery disease like obesity, and high blood pressure and high cholesterol levels.
- Taking care of teeth and gums- there is an associated link between endocarditis i.e. an infected heart tissue and gingivitis i.e. infected gums.
Aortic Stenosis could make life difficult and hence it is very important to prevent it right at the root. In case it has already happened, abiding by the treatment protocol is very crucial and so is maintaining the restrictions post the surgical methods.