Aortic stenosis

From greek.doctor

Aortic stenosis (AS) refers to narrowing of the aortic valve, resulting in increased pressure load on the left ventricle. AS is mostly a disorder of the elderly (>70 years) men, and it’s the most common valvular disease. Some also have some degree of aortic regurgitation.

Most cases are discovered incidentally when a systolic murmur is heard. The condition is asymptomatic for years or decades before symptoms develop.

Etiology

In most cases, aortic stenosis is a result of dystrophic calcification and degeneration of the aortic valve with age. 1 – 2% of the population have a congenital bicuspid aortic valve, which predisposes to aortic stenosis and causes it to occur at younger ages (<70 years).

In developing countries, rheumatic fever remains a significant cause.

Pathophysiology

A stenotic aortic valve means an increased obstruction of the left ventricle's outflow. Initially the left ventricle can overcome the increased resistance, but this causes concentric hypertrophy and remodelling of the left ventricle. The compliance of the left ventricle is reduced. This may lead to diastolic heart failure (heart failure with preserved ejection fraction, HFpEF).

Because of the reducing compliance of the left ventricle, the ventricle is more dependent on the left atrial contraction for filling than in a healthy heart. If atrial fibrillation should occur, this atrial contraction is lost, worsening the patients symptoms.

Marked left ventricular hypertrophy may compress the coronary vasculature in diastole, potentially inducing ischaemia even in the absence of coronary artery disease. This causes the characteristic angina.

Syncope may occur because the left ventricle cannot generate enough pressure to increase the minute volume when the peripheral vasculature resistance increases, for example during exercise.

Clinical features

Patients usually progress from asymptomatic to symptoms during exertion to symptoms in rest. Symptoms only occur when the stenosis is severe. The most common symptom is dyspnoea and exercise intolerance, but other symptoms include angina and syncope.

A systolic crescendo-decrescendo ejection murmur is typical. It’s best heard at the punctum maximum of the aortic valve, parasternally in the 2nd right intercostal space. It may radiate to the carotids. Soft S2 is also a typical finding.

Diagnosis and evaluation

Echocardiography allows for assessment of the narrowing of the aortic valve opening area and the pressure gradient and velocity across the valve, which is increased in case of stenosis. It can also detect whether the aortic valve is bicuspid or tricuspid. Coronary angiography can be used to assess the degree of coronary artery disease, which is useful as pre-operative assessment if surgical treatment is considered.

A chest radiograph may show enlarged left border of the heart and dilation of the ascending aorta. ECG-gated CT of the heart is obligatory pre-operative assessment for valve replacement.

Treatment

In mild cases, regular follow-up alone might be sufficient, but the only definitive treatment is valvular replacement. This can be achieved by open surgery (surgical aortic valve replacement, SAVR) or transcatheter replacement (transcatheter aortic valve replacement, TAVR). If significant CAD is present, coronary bypass can be performed in the same setting as the surgical replacement of the valve.

Endovascular replacement (TAVR) is usually recommended to those with unacceptable surgical risk, as there isn't as much documentation on the long-term results of TAVR compared to surgical replacement (SAVR). The latter is recommended to those who are younger and less comorbid.

Antihypertensive treatment, preferably with RAAS inhibitor, is recommended to reduce the afterload of the left ventricle and to prevent ventricular remodelling.

Dental evaluation, to rule out or treat dental infections, is routine before valvular surgery to reduce the risk of infective endocarditis.

Complications