Aortic Stenosis: Definition, Etiology, and Bicuspid Valve

• Aortic stenosis is the most common type of heart valve disease, affecting millions of people in the US.
• The condition commonly affects people 65 and older, impacting 1 in 8 individuals over 75.
• Leaflets stiffen over time, reducing ability to fully open and close.
• The heart works harder to push blood through the aortic valve when leaflets don't fully open.
• Less oxygen-rich blood flows to the brain, causing heart failure symptoms.

Definition

• Aortic stenosis is defined as the narrowing of the aortic valve orifice.

Etiology

• Degenerative aortic stenosis is age related fibrocalcific, with a mean age of onset between 65 to 70 years.
• Congenital causes include unicuspid, bicuspid aortic valve, or quadracuspid valves.
• Rheumatic fever is an inflammatory cause of Aortic Stenosis

Bicuspid Aortic Valve

• Congenital unicuspid, bicuspid, or quadracuspid valves can cause aortic stenosis.
• Presence of a bicuspid aortic valve can be evaluated using the parasternal short-axis view of the aortic valve in systole.
• A "Raphe" (an underdeveloped aortic cusp) may give the appearance of three leaflets in diastole.
• M-Mode may be used to determine bicuspid aortic valve
• An index ≥ 1.5 indicates a bicuspid aortic valve, found in 74% of surgically or angiographically proved cases.
• A normal eccentricity index (< 1.5) does not exclude the presence of a bicuspid aortic valve.

Rheumatic heart disease

• Rheumatic heart disease is a condition where the heart valves have been permanently damaged by rheumatic fever.
• Rheumatic fever is an inflammatory disease affecting many connective tissues, especially in the heart.
• Untreated or undertreated strep infections increases a person's risk.

Signs and Symptoms

• Depending on the severity, angina pectoris may occur.
• Syncope or near syncope can be a symptom.
• Other symptoms include shortness of breath, fatigue, and palpitations.

Complications

• Left ventricular pressure overload results in hypertrophy.
• Increased left ventricular end-diastolic pressure causes diastolic dysfunction.
• Increased left atrial pressure causes left atrial enlargement.
• It can lead to left ventricular systolic dysfunction and dilatation (late in course).
• Global hypokinesis (late in course) may be seen.
• Increased pulmonary artery pressures, including increased TR and dilated IVC.
• There is an increased risk of infective endocarditis.
• There also exists an Increased risk of sudden death.

Cardiac Auscultation

• A harsh, systolic ejection murmur, crescendo-decrescendo in shape, may be heard.
• It is best heard at the right upper sternal border, which may radiate into the carotid arteries.
• S4 may be heard.
• Pulsus parvus et tardus (slow-rising, late-peaking carotid pulse) may be present.

Complimentary Modalities

• Electrocardiogram may show left ventricular hypertrophy, left atrial enlargement or atrial fibrillation.
• Chest X-ray may reveal cardiomegaly, calcification, or post-stenotic dilatation of the ascending aorta.

Cardiac Catheterization

• Peak-to-peak and mean pressure gradients can be determined.
• The aortic valve area is determined by the Gorlin formula: AVA (cm2) = (CO / SEP) / (43.3 x MPG).
• AVA is the aortic valve area.
• CO is cardiac output.
• SEP is the systolic ejection period.
• 43.3 is the constant
• MPG is the mean pressure gradient.
• M-Mode is aortic stenosis signature

M-Mode Degenerative/Rheumatic

• Increased thickness of aortic valve leaflets may be seen.
• Decreased excursion of aortic valve leaflets (< 15 mm) may be seen.
• Absence of systolic flutter of the aortic valve leaflets may be present.
• Left ventricular hypertrophy may exist.
• Left atrial enlargement may occur.
• 2-D echocardiography shows thickened aortic valve leaflets, systolic "doming'' and diastolic "doming" (aortic valve prolapse).
• A football-shaped opening of the aortic valve is best seen in the parasternal short-axis view.
• In 2-D, thickness of aortic valve leaflets is increased, as is decreased excursion of leaflets (< 15 mm).
• Post-stenotic dilatation of the ascending aorta occurs, together with left ventricular hypertrophy and left atrial enlargement.
• Left ventricular systolic function decreases (late in course).

Doppler Assessment

• Peak aortic velocity, maximum instantaneous pressure gradient and mean transvalvular pressure gradient is determined.
• Aortic valve area is determined(continuity equation).
• Velocity ratio is determined.

Important to Note

• Perform Blind Probe analysis (Pedoff).

• Examine the aortic valve from several windows using CW Doppler (Pedoff).

• Ensure that that the ultrasound beam is parallel to flow to ensure the highest velocity across the aortic valve is obtained.

• Catheterization measures the peak-to-peak gradient, while Doppler determines the maximum instantaneous pressure gradient.

• Compare Doppler results to the mean gradient and aortic valve area with the Catheterization findings.

• Evaluate left ventricular systolic function because it has a direct effect on the peak velocity of the aortic valve.

• Aortic regurgitation is 3+ or 4+ determine the aortic valve area.

• Significant AR increases the velocity across the aortic valve, causing stenosis to be overestimated.

• Take care not to confuse mitral regurgitation with the aortic stenosis jet, which is longer because there is no flow during the Isovolumic contraction or Isovolumic relaxation period through the aortic valve.

• In addition, mitral regurgitation usually has a greater velocity than aortic stenosis.

• This is because the pressure gradient between the left ventricle and aorta is less than that between the left ventricle and left atrium.

• An asymmetric triangular contour with an early peaking of the jet usually indicates mild aortic stenosis.

• Symmetric and rounded velocity contour with a late peaking jet velocity (peak > 50% of total ejection time) is usually seen in severe aortic stenosis.

• It may be difficult to differentiate a bicuspid aortic valve from an acquired aortic stenosis.

• Aortic stenosis due to a bicuspid aortic valve usually becomes symptomatic at age 20 to 50, while calcific aortic stenosis occurs in the elderly.

Steps in Determining LVOT value

• Measure the LVOT diameter just below the aortic valve in the parasternal long axis view.
• Calculate the CSA : CSA=.785(D) ^2
• Measure the velocity of the LVOT with PW Doppler from the apical 5 chamber to the maximal velocity just beyond the Aortic Valve.
• Measure the velocity of the LVOT with CW Doppler from the apical, suprasternal, supraclavicular, left parasternal, right parasternal, and subcostal positions
• The aortic valve surface area in cm2 is determined as AVA =CSA(LVOT) 2* (Vmax LVOT) / (Vmax AV)

Aortic Stenosis – Continuity Equation

• AVA(Vmax) = CSA(LVOT) * (Vmax LVOT) / (Vmax AV)
• AVA (VTI) = CSA(LVOT) * (VTI LVOT) / (VTI AV)
• AVA (Vmean) = CSA(LVOT) * (Vmean LVOT) / (Vmean AV)

Peak Aortic Velocity Values

• Normal: <2.0 m/s
• Mild: ≥ 2.5 m/s as long as reduced opening excursion is demonstrated.
• Moderate: 3.0 to 4.0 m/s
• Severe: >4.0 m/s

American Society of Echocardiography guidelines for aortic stenosis

• Normal peak velocity is 1.35 or 1.0-1.7 (m/sec)
• Normal maximum instantaneous pressure gradient is 3-5 (mmHg)
• Valve area of >1.1(cm²/m²) is normal and <30 mean transvalvular pressure gradient.
• Mild cases have peak velocity < 3.0 (m/sec), instantaneous pressure gradient of 16-36 (mmHg, mean transvalvular pressure gradient of <30 (mmHg,) valve area of >1.5 (cm²) and indexed valve area between 0.9-1.1.
• Moderate cases have peak velocity of 3.0-4.0 (m/sec), an instantaneous pressure gradient of 36-50 (mmHg), a mean transvalvular pressure gradient of 30-50 (mmHg),a valve area of 0.75 - 1.0 (cm²), indexed valve area between 0.6-0.9.
• For severe aortic stenosis, peak velocity is > 4.0 (m/sec), instantaneous pressure gradient is > 50 (mmHg), mean transvalvular pressure gradient > 50 (mmHg), valve area < 0.75 (cm²),indexed valve area < 0.6.

Common Errors

• Common errors in assessing aortic stenosis include not being parallel to blood flow and the presence of mitral regurgitation.
• Velocity, frequency, and angle all determine the frequency of sound waves in blood flow
• The angle between the ultrasound beam and direction of flow should be zero (0).
• Any angle other than zero will cause underestimation of the true velocity
• Avoid "feathering" or small linear signals outside of the true envelope.
• Mitral regurgitation presents flows commonly in the isovolumic periods where velocities are generally higher than aortic stenosis.
• Premature ventricular contractions can cause errors.
• Premature beat has a shorter diastolic filling period and therefore has a smaller stroke volume whereas the beat proceeding a premature beat has a longer diastolic filling period .
• Dimensionless indexing describes dimensionless Index in Patients With Low-Gradient Severe Aortic Stenosis and Preserved Ejection Fraction .