Clinical features

Aortic stenosis is a common condition, with a normal aortic valve area of between 2-4 cm2 and moderate stenosis defined as 1-1.5 cm2 and severe as <1 cm2. To preserve stroke volume, the left ventricle will often compensate by becoming hypertrophied.  Thus, patients may have aortic stenosis for a number of years before becoming symptomatic.

Pure aortic stenosis usually manifests after six to eight decades of progressive obstruction. Onset of symptoms is one to two decades earlier for patients with bicuspid aortic valve disease.

Patients with aortic stenosis presents with:

  • Exertional dyspnoea – Reduced left ventricular (LV) compliance elevates both LV diastolic pressure and pulmonary capillary pressure. Dyspnoea accompanies fatigue, exercise intolerance and reduced activity.
  • Angina pectoris – develops late due to impaired coronary sinus filling; compression of coronary vessels from hypertrophy and an increased myocardial demand from hypertrophied muscle. Coronary artery disease will commonly be present.
  • Syncope – For a static cardiac output, vasodilation in exercising muscle and impaired vasoconstriction in non-exercising muscle causes arterial pressure to drop.

Late-stage aortic stenosis is associated with all the clinical manifestations of impaired cardiac output: weakness, fatigue, peripheral cyanosis and cachexia. In the advanced stage, failure of the left ventricle may co-occur resulting in pulmonary oedema, orthopnoea, and paroxysmal nocturnal dyspnoea due to decompensated heart failure.

Findings associated with late, isolated, and severe aortic stenosis:

  • Tricuspid regurgitation
  • Marked pulmonary hypertension, resulting in:
    • Right ventricular failure
    • Systemic venous hypertension
    • Hepatomegaly
    • Atrial fibrillation

Initial investigation

The evaluation of aortic stenosis is typically performed with echocardiography, although cardiovascular magnetic resonance is becoming increasingly common for initial assessment. The echocardiogram is used in the parasternal view to visually assess valvular morphology.

The pressure gradient across the valve (and valve area) is used to estimate the extent of aortic stenosis.

In patients with aortic stenosis, systemic arterial pressure is usually unremarkable. When stroke volume begins to decline, systolic pressure may fall and pulse pressure narrow. A shudder may be palpable, most commonly over the left carotid artery. The a wave in the JVP may become more prominent.

  • Auscultation. The murmur of aortic stenosis is classically a mid-systolic ejection murmur heard immediately after S1. It’s heard most reliably over the right second intercostal space. Intensity of the murmur increases until the middle of ejection, drops off, and ends just before closure of the aortic valve. It is heard loudest at the base of the heart, and sounds low-pitched, rasping and rough. The intensity of S2 is often reduced in critical aortic stenosis with delayed A2 (due to delayed closure of the aortic valve).
  • Echocardiogram. LV hypertrophy, diminished systolic opening of the leaflets, and calcification are usually reported.
  • ECG. T-wave inversion in I and aVL due to left ventricular strain with ST depression and evidence of left ventricular hypertrophy.
  • Chest Radiography. Cardiac dilation may not manifest until late-stage aortic stenosis. LV hypertrophy with no enlargement rounds the apex. Valve calcification may be apparent in the lateral view, as well as dilation of the ascending aorta in the frontal view. LV enlargement is marked in late-stage aortic stenosis.
  • Catheterization. Indicated when other clinical findings are discrepant or in special circumstances due to risk of cerebral embolization.

Underlying pathology

Aortic stenosis is among the most common forms of valvular heart disease. Gradual calcification can occur in both normal and congenitally abnormal valves. Abnormal cusp development are some of the most common congenital heart defects. Bicuspid aortic valves are particularly vulnerable to aortic stenosis and aortic insufficiency.

Aortic stenosis appears most commonly in patients with bicuspid aortic valve disease, tri-leaflet deterioration, or prior rheumatic fever.  Aortic stenosis is a degenerative calcification of the aortic cusps. Inflammatory signaling, endothelial dysfunction, and lipid accumulation contribute to the disease process.

A pressure gradient is created due to obstructed left ventricular outflow. Because obstruction occurs gradually, concentric LV hypertrophy develops to maintain cardiac performance. When excessive hypertrophy becomes maladaptive, LV systolic function deteriorates and myocardial fibrosis develops. Impaired LV compliance is evident by elevated LV end-diastolic pressure and preserved ejection fraction. In patients with aortic stenosis, cardiac output fails to increase during exercise, but is relatively normal at rest.

Late-stage aortic stenosis has the following pathophysiological features:

  • Declining contractile function, cardiac output and pressure gradient between the LV and aorta
  • Increased pulmonary artery, mean left atrial, and RV pressures
  • Hypertrophy erodes stroke volume and cardiac output (when ejection fraction is preserved and LV enlargement is absent)
  • Left ventricular hypertrophy increases myocardial O2 demands.

Treatments

  • Digoxin, diuretics and sodium restriction before operation are indicated in patients with reduced cardiac reserve
  • Enlargement of the aortic root can be addressed with beta blockers, angiotensin receptor blockers and ACE inhibitors
  • Valvuloplasty can be useful for asymptomatic adolescents with critical aortic stenosis in order to postpone the need for cardiac surgery. It may also provide short-term benefits for patients who can’t tolerate aortic valve replacement.

Aortic valve replacement

  • AVR is considered definitive therapy for severe aortic stenosis, but carries a 1-3% mortality in patients younger than 70 years and 4-8% in older patients;
  • Class I evidence indications for AVR include:
    • Early valve replacement is recommended in all symptomatic patients with severe AS without a surgical contraindication;
    • AVR is indicated in patients with severe AS undergoing CABG, ascending aorta surgery, or surgical procedures on another valve;
    • AVR is indicated asymptomatic aortic stenosis with severe AS and either LVEF <50% not due to another cause or an abnormal exercise test showing symptoms on exercise clearly related to AS;
  • The management of asymptomatic aortic stenosis is controversial.  Decisions are usually taken by a multidisciplinary team discussion in the UK;
  • Transcatheter aortic valve implantation (TAVI) is an alternative to surgical aortic valve replacement in patients with symptomatic severe aortic stenosis who are not fit for surgical valve replacement.

References

Baumgartner H. Aortic stenosis: medical and surgical management. Heart. 2005;91(11):1483-8.

Carabello BA, Paulus WJ. Aortic stenosis. Lancet. 2009;373(9667):956-66.

Sawaya F, Liff D, Stewart J, Lerakis S, Babaliaros V. Aortic stenosis: a contemporary review. Am J Med Sci. 2012;343(6):490-6.