Aortic stenosis
Aetiology
Congenital AS typically manifests early in life, mainly in childhood and infancy.
Most common cause of AS however, is calcification of normal tricuspid or congenitally bicuspid aortic valve.
In addition, rheumatic disease can rarely also involve the aortic valve.
Several other conditions, such as atherosclerosis of the aorta in patients with severe hypercholesterolemia or ochronosis with alkaptonuria are also sometimes cause of AS.
Epidemiology
Prevalence of aortic stenosis (AS) increases with age and approx. 1-2% of persons older than 65 and 12% of persons older than 75 have calcific AS.
As the population ages, the prevalence of AS is expected to rise.
Symptoms
Patients can be diagnosed before the symptom onset by auscultation or they can present with one or more of the following symptoms: gradual decrease in exercise tolerance, fatigue, exertional dyspnea and/or angina and/or syncope.
Auscultation
An ejection systolic murmur can be heard best at the base of the heart (right second intercostal space). It radiates to the carotid arteries and has a late peaking crescendo-decrescendo character. It decreases with standing or handgripping.
Diagnostics
The diagnosis of AS is usually established by echocardiography, which is now the gold standard for assessing the morphology of the valve, presence of stenosis and its severity and it also allows for evaluation of other pathologies and ventricle function.
Additionally, cardiac CT is now used to obtain precise measurements needed when an aortic valve replacement is being considered or planned.
Echocardiography
Currently recommended parameters that should be routinely obtained to evaluate the severity of AS are (Image 1):
1) Left Ventricular Outflow Tract (LVOT) diameter
2) LVOT velocity
3) AS jet velocity
4) Valve anatomy
Video 1 - Moderate AS in the PLAX view with Colour Flow Doppler (increased flow velocities apparent in colour doppler imaging)
Video 2 - Severe AS in the PLAX view - valve is bicuspid and heavily calcified with restricted movement of the cusps.
Video 3 - Severe AS in the PLAX view with Colour flow doppler (increased flow velocities)
Video 4 - Severe AS documented in the A3C view with CFD, also marked concentric LV hypertrophy present
Video 5 - PSAX at the level of the Aortic Valve - normal anatomy of the AV with 3 cusps is seen.
Video 6 - PSAX at the level of the Aortic Valve - heavily degenerated and calcified bicuspid AV
Video 7 - The same PSAX view at the level of AV with colour flow doppler
The severity of AS is assessed based on peak velocity, mean gradient and area of the aortic valve (AVA). The grading of AS is summarized in this table (Image 2).
Adapted from: Baumgartner H, Hung J, Bermejo J, et al. Recommendations on the Echocardiographic Assessment of Aortic Valve Stenosis: A Focused Update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography. J Am Soc Echocardiogr. 2017 Apr;30(4):372-392.
1) Peak Jet velocity
It is the maximum speed of blood flow across the stenotic valve area.
How is it measured ?
It is measured using continuous-wave (CW) Doppler (CWD) ultrasound across multiple acoustic windows in order to determine the highest velocity.
Usually, the velocity is highest in apical (five or three chamber view) and right parasternal or suprasternal view.
The outer edge of the spectral Doppler envelope is traced to provide both the velocity–time integral (VTI) for the continuity equation and the mean gradient. Three or more beats should be averaged for patients in sinus rhythm. Averaging more beats is mandatory with irregular rhythms (at least 5 consecutive beats). Special care must be taken to select representative sequences of beats and to avoid post-extrasystolic beats.
The shape of the CWD velocity curve is helpful in distinguishing the level and severity of obstruction. Although the time course of the velocity curve is similar for fixed obstruction at any level (valvular, subvalvular, or supravalvular), the maximum velocity occurs later in systole and the curve is more rounded in shape with more severe obstruction.
With mild obstruction, the peak is in early systole with a triangular shape of the velocity curve, compared with the rounded curve with the peak moving towards mid systole in severe stenosis, reflecting a high gradient throughout systole.
The shape of the CWD velocity curve also can be helpful in determining whether the obstruction is fixed or dynamic. Dynamic subaortic obstruction shows a characteristic late-peaking velocity curve, which is usually concave upward in early systole.
- Mild stenosis: 2.0 – 2.9 m/s
- Moderate stenosis: 3.0 – 3.9 m/s
- Severe stenosis: > 4.0 m/s
- Very Severe or Critical stenosis: > 5.0 m/
2) Mean pressure gradient
The pressure difference between the left ventricle (LV) and aorta in systole, or transvalvular aortic gradient, is another standard measure of stenosis severity.
The calculation of the mean gradient, the average gradient across the valve occurring during the entire systole, has potential advantages and should be reported.
Transaortic pressure gradient (ΔP) is calculated from velocity (v) using the simplified Bernoulli equation as: ΔP=4v2.
- Mild stenosis: < 20 mmHg
- Moderate stenosis: 20 – 39 mmHg
- Severe stenosis: ≥ 40 mmHg
3) Aortic valve area (AVA)
Doppler velocity and pressure gradients are flow dependent. For a given orifice area, velocity, and gradient increase with an increase in transaortic flow rate, and decrease with a decrease in flow rate. Calculation of the stenotic orifice area or effective aortic valve area (AVA) is particularly important when flow rates are very low or very high, although even the degree of valve opening varies to some degree with flow rate.
AVA is calculated by using the continuity-equation which is based on the concept that the stroke volume (SV) ejected through the LV outflow tract (LVOT) all passes through the stenotic orifice (AVA) and thus SV at valve orifice level is equal to the LVOT SV.
How is it measured?
- LVOT diameter for calculation of the crossectional area
- LVOT velocity recorded with pulse wave Doppler
- AS jet velocity by CWD
- >0.85 cm2/m2 = mild AS
- 0.60-0.85 cm2/m2 = moderate AS
- <0.6 cm2/m2 = severe AS
Image 3 Mild/Moderate AS (Pmax - 27 mmHg, Pmean - 20 mmHg, Vmax - 2.62)
Image 4 Severe AS (Pmax - 66 mmHg, Pmean - 41 mmHg, Vmax - 4.05 m/s)
Image 5 Critical AS (Pmax - 119 mmHg, Pmean - 85 mmHg, Vmax - 5.46 m/s)
LV outflow tract (LVOT) stroke volume
In all patients with aortic stenosis, it is necessary to obtain stroke volume (SV) measurement.
How is the LVOT stroke volume measured?
Accurate SV calculations depend on precisely measuring 1) the cross-sectional LVOT area (CSA) and 2) LVOT velocity.
1) The current standard approach to estimate the LVOT CSA that is still commonly used is based on LVOT diameter measurements.
LVOT diameter is measured in a parasternal long-axis view from the inner edge to inner edge of the septal endocardium, and the anterior mitral leaflet in mid-systole.
Usually three or more beats are averaged in sinus rhythm, averaging of more beats is appropriate with irregular rhythms (at least five consecutive beats).
2) LVOT velocity is recorded with pulsed Doppler from an apical approach, in either the anteriorly angulated four-chamber view (5-chamber view) or in the apical long-axis view (3-chamber view). The pulsed Doppler sample volume is positioned just proximal to the aortic valve (Image 5)
Image 6 LVOT diameter is measured in the PLAX view zoomed to LVOT and AV
Image 7 LVOT velocity measured with Pulsed-wave doppler in the apical 5-Chamber view with the sample placed on the LV side of the AV in the LVOT
Image 8 How to measure Cardiac output based on echo examination
Doppler Velocity Index (DVI)
Marker of aortic stenosis severity, eliminates errors of LVOT measurement.
DVI = VTI LVOT / VTI AV
This peak velocity ratio is dimensionless and does not rely on determination of cross-sectional area of the LVOT thus making it less dependent on valve size and especially useful when the valve size is not known.
Image 9 Definition of aortic stenosis based on DVI
Types of AS based on flow and gradient
Patients with AVA <1cm2 and mean gradient of >40mmHg and/or peak velocity of >4m/s are classified as having severe AS.
However, the situation is more complex when AVA is <1cm2 but the other criteria are not met. In such cases, further differential diagnosis needs to be performed to asses the true severity of AS.
In the following table, a step by step diagnostic approach is recommended by the current ESC guidelines.
Image 10 Aortic stenosis management
Vahanian A, Beyersdorf F, Praz F, et al. ESC/EACTS Scientific Document Group. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J. 2021 Aug 28:ehab395. doi: 10.1093/eurheartj/ehab395. Epub ahead of print. PMID: 34453165.
Several possible conditions can cause the discordance in the data. The patient can have AVA <1cm2 but only have moderate AS. It is important to distinguish these patients from those with some form of atypical severe AS.
!!! Low-flow, low-gradient AS with reduced ejection fraction (LVEF ≤ 40 %, CI < 3.0 l/min/m2 or a SV < 35ml/m2).
Patients may have AVA <1cm2 at rest, but when dobutamine is administered during stress ECHO AVA increases. This is called pseudosevere AS.
In a true severe AS, the AVA does not increase and the condition is called low-flow, low-gradient AS with reduced ejection fraction.
!!! Low-flow, low-gradient AS with preserved ejection fraction (paradoxical severe aortic stenosis)
This condition is commonly found in the elderly patients with small ventricles, hypertrofic myocardium associated with left ventricular compliance reduction leading to a "low-flow" state, defined by an ejected volume (stroke volume) of < 35 ml/m2.
The most common history in these patients is hypertension. Diagnosis can be challenging and other imaging modalities should be used to confirm the diagnosis - aortic valve calcium score, dobutamine stress echocardiogram to see if stroke volume increases under stress, heart catheterization to check accuracy of low cardiac output.
!!! Definition of Paradoxical severe aortic stenosis :
Aortic valve area ≤ 1 cm2, mean transvalvular pressure gradient <40 mm Hg, normal EF and low transvalvular flow, defined as stroke volume index <35 mL/m2.
Valve replacement may be indicated for symptomatic patients with severe paradoxical low-flow aortic stenosis.
Management of AS
There is currently no medical therapy that would alter the prognosis of patients with severe AS. However, interventions in the form of surgical aortic valve replacement (SAVR) or transcatheter aortic valve replacement/implantation (TAVR/TAVI) can be performed and both have proven mortality benefits.
Echocardiographic assessment of the severity of AS plays a key role in the indication for an intervention together with clinical status of the patient and other additional tests. The indications for intervention are the same for both SAVR and TAVI in patients with symptomatic severe AS.
All patients with severe symptomatic AS are indicated for an intervention, including patients with low-flow low-gradient AS with reduced ejection fraction and low-flow low-gradient AS with preserved ejection fraction.
The choice between SAVR or TAVI should be made by a Heart Team and depends on multiple factors.
Image 11 The complete list of indications recommended by the current guidelines
Vahanian A, Beyersdorf F, Praz F, et al. ESC/EACTS Scientific Document Group. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J. 2021 Aug 28:ehab395. doi: 10.1093/eurheartj/ehab395. Epub ahead of print. PMID: 34453165.
Vahanian A, Beyersdorf F, Praz F, et al. ESC/EACTS Scientific Document Group. 2021 ESC/EACTS Guidelines for the management of valvular heart disease. Eur Heart J. 2021 Aug 28:ehab395. doi: 10.1093/eurheartj/ehab395. Epub ahead of print. PMID: 34453165.
Although the decision of whether to perform SAVR or TAVI is individualized, the current guidelines offer a step by step approach to the decision making process provided in a table above.
Risk of surgery and technical feasibility among other factors need to be considered. Indications for TAVI are evolving and currently, it has a proven mortality benefit over SAVR in very high-risk patients and comparable outcomes for high-risk patients. It does have limitations as the longevity of the bioprosthesis used in TAVI is currently unknown. Patients with bicuspid valves have been excluded from major TAVI trials, although it is technically possible to perform TAVI on a bicuspid valve.
The management of asymptomatic patients with severe AS is also controversial and indications for SAVR are provided in the table above. TAVI is currently not recommended for asymptomatic patients with severe AS.
References
- From: Alec Vahanian, Friedhelm Beyersdorf, Fabien Praz, Milan Milojevic, Stephan Baldus, Johann Bauersachs, Davide Capodanno, Lenard Conradi, Michele De Bonis, Ruggero De Paulis, Victoria Delgado, Nick Freemantle, Martine Gilard, Kristina H Haugaa, Anders Jeppsson, Peter Jüni, Luc Pierard, Bernard D Prendergast, J Rafael Sádaba, Christophe Tribouilloy, Wojtek Wojakowski, ESC/EACTS Scientific Document Group, 2021 ESC/EACTS Guidelines for the management of valvular heart disease: Developed by the Task Force for the management of valvular heart disease of the European Society of Cardiology (ESC) and the European Association for Cardio-Thoracic Surgery (EACTS), European Heart Journal, 2021;, ehab395, https://doi.org/10.1093/eurheartj/ehab395
- Recommendations on the echocardiographic assessment of aortic valve stenosis: a focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography, Helmut Baumgartner, (chair), Judy Hung, (co-chair), Javier Bermejo, John B. Chambers, Thor Edvardsen, Steven Goldstein, Patrizio Lancellotti, Melissa LeFevre, Fletcher Miller, Jr, Catherine M. Otto, European Heart Journal - Cardiovascular Imaging, Volume 18, Issue 3, March 2017, Pages 254–275, https://doi.org/10.1093/ehjci/jew335
- Aortic valve stenosis: evaluation and management of patients with discordant grading, David Messika-Zeitoun, Guy Lloyd, E-Journal of Cardiology Practice, Vol. 15, N° 26 - 10 Jan 2018, available from: https://www.escardio.org/Journals/E-Journal-of-Cardiology-Practice/Volume-15/Aortic-valve-stenosis-evaluation-and-management-of-patients-with-discordant-grading
- Zipes, Peter Libby, Robert O. Bonow ; founding editor and online editor Eugene Braunwald. Braunwald's Heart Disease : a Textbook of Cardiovascular Medicine. Philadelphia, PA :Elsevier/Saunders, 2015
