ECHOCARDIOGRAPHIC ASSESSMENT OF AORTIC STENOSIS

Dr Julian Johny Thottian

Aorta - anatomy

Eur J Echocardiogr 2009;10:i3-10

Normal Aortic valve

Three cusps, crescent shaped 3 commissures

3 sinuses supported by fibrous

annulus

3.0 to 4.0 cm2

Node of Arantius

PLAX

ZOOMED PLAX

The long-axis view of the left ventricle corresponding with the echocardiographic parasternal long-axis view, demonstrating the extent of the aortic root.

Piazza N et al. Circ Cardiovasc Interv 2008;1:74-81

Copyright © American Heart Association

M MODE M MODE

PSAX

VARIOUS MEASUREMENTS

Evangelista A, Flachskampf FA, Erbel R et al. Echocardiography in aortic diseases: EAE recommendations for clinical practice. Eur J Echocardiogr 2010;11:645-58

VS 2.8+/- 0.3

STJ 2.4+/- 0.4

AAoAA

2.6+/- 0.31.9+/- 0.2

2D - Apical five chamber view

2D – Suprasternal view

3D ECHO

TEE

Aortic stenosis- Causes

Most common :-Bicuspid aortic valve with calcificationSenile or Degenerative calcific ASRheumatic AS

Less common:-CongenitalType 2 HyperlipoproteinemiaOochronosis

ANATOMIC CONSIDERATIONS

Calcified aortic valve

Most prominent in the central part of each cusp Commissural fusion absent Stellate-shaped systolic orifice.

Valve calcification Mild - few areas of dense echogenicity with little

acoustic shadowing Severe- extensive thickening and increased echogenicity with a prominent acoustic shadow.

Valve calcification - predictor of clinical outcome.

Calcific Aortic Stenosis

Calcification of a bicuspid or tricuspid valve, the severity can be graded semi-quantitatively as

0 1+ 2+ 3+ 4+ Schaefer BM et al.Heart 2008;94:1634–1638.

The degree of valve calcification is a predictor of clinical outcome. Rosenhek R et al. N Engl J Med 2000;343:611–7.

Calcific Aortic Valve

Bicuspid Aortic Valve

Fusion of the RCC & LCC -80% of cases. Fusion of the RCC & NCC-20% of cases. Fusion of the LCC and NCC is rare.

Bicuspid Aortic Valve

Rheumatic aortic stenosis

Rheumatic AS - commissural fusion Triangular systolic orifice

Thickening and calcification mostly along the edges of the cusps.

Concomitant involvement of mitral valve seen

Subvalvular aortic stenosis(1) Thin discrete membrane consisting of

endocardial fold and fibrous tissue(2) A fibromuscular ridge (3) Diffuse tunnel-like narrowing of the

LVOT(4) accessory or anomalous mitral valve

tissue.

Supravalvular Aortic stenosisType I - Thick, fibrous ring above the aortic valve with less mobility and has the easily identifiable 'hourglass' appearance of the aorta.

Supravalvular Aortic stenosis

Type II - Thin, discrete fibrous membranelocated above the aortic valve

The membrane usually mobile and may demonstrate doming during systole

Type III- Diffuse narrowing

AORTIC VALVE ASSESSMENT

There are many Echo criteria for assessment of Aortic stenosis

Let’s focus on the ones used in daily practice.

RECOMMENDATIONS FOR STANDARD CLINICAL PRACTICE LEVEL A- ESC 2009

● AS jet velocity● Mean trans aortic gradient● Valve area by continuity equation.

AS JET VELOCITY

Jet Velocity

This is measured with Continuous wave doppler

Multiple windows and “non-standard views” to look for the highest Vmax

Apical and Suprasternal or right parasternal most frequently yield the highest velocity;

Subcostal or Supraclavicular windows may be required.

Aortic Jet Velocity

Patient positioning Adjustment of transducer position Angle - velocity measurement assumes a parallel intercept angle between the ultrasound beam and direction of blood flow

AS jet velocity is defined as the

highest velocity signal obtained from any window

Aortic Jet Velocity Pitfalls Any deviation from a parallel

intercept angle results in velocity

underestimation- degree of underestimation is 5% or less if the intercept angle is within 15° of parallel.

“Angle correction” should not be used.

Continuous-wave Doppler of severe aortic stenosis jetshowing measurement of maximum velocity and tracing of thevelocity curve to calculate mean pressure gradient.

Mean transvalvular gradient

The difference in pressure between the left ventricle and aorta in systole

Gradients are calculated from velocity information

It is the mean of different instantaneous velocities recorded

Bernoulli equations ΔP =4v²

The maximum gradient is calculated from maximum velocity

ΔP max =4v² max

The mean gradient is calculated by averaging the instantaneous gradients over the ejection period

Mean transvalvular gradient

Mean transvalvular gradient

The simplified Bernoulli equation assumes that the proximal velocity can be ignored

When the proximal velocity is over 1.5 m/s or the aortic velocity is <3.0 m/s, the proximal velocity should be included in the Bernoulli equation ΔP max =4 (v² max- v2

proximal)

Sources of error for pressure gradient calculations

Malalignment of jet and ultrasound beam.Recording of MR jet

Other Sources of error for pressure gradient calculations

Neglect of an elevated proximal velocity.

Any underestimation of aortic velocity results in an even greater underestimation in gradients, due to the squared relationship between velocity and pressure difference

The accuracy of the Bernoulli equation to quantify AS pressure gradients is well established

Pressure recovery

The conversion of potential energy to kinetic energy across a narrowed valve results in a high velocity and a drop in pressure.

Distal to the orifice, flow decelerates again. Kinetic energy will be reconverted into potential energy with a corresponding increase in pressure, the so-called PR

Pressure recovery

Pressure recovery is greatest in stenosis with gradual distal widening

Aortic stenosis with its abrupt widening from the small orifice to the larger aorta has an unfavorable geometry for pressure recovery

PR= 4v²× 2EOA/AoA (1-EOA/AoA)

Cath Vs Echo

Comparing pressure gradients calculated fromdoppler velocities to pressures measured at cardiac catheterization.

Currie PJ et al. Circulation 1985;71:1162-1169

Continuity Equation

Schematic diagram of continuity equation. The assumption is that SV LVOT = SV Aortic Valve

Continuity Equation

Calculation of continuity-equation valve area requires three measurements: AS jet velocity by CWD LVOT diameter for calculation of a

circular CSA LVOT velocity recorded with pulsed

Doppler.

Continuity Equation

LVOT diameter and PW of the LVOT needs to taken from the same location in the LVOT.

LVOT diameter measured- PLAX view LVOT velocity (or VTI) is measured apically

– beware of distance error. The pulsed-Doppler sample volume is

positioned just proximal to the aortic valve so that the location of the velocity recording matches the LVOT diameter measurement.

LVOT Diameter

• Left ventricular outflow tract diameter is measured in the parasternal long-axis view in mid-systole from the white–black interface of the septal endocardium to the anterior mitral leaflet, parallel to the aortic valve plane and within 0.5–1.0 cm of the valve orifice.

Velocity or VTI measurement

LVOT velocity is measured from the apical approach either in an apical long-axis view or an anteriorly angulated four-chamber view An optimal signal shows a smooth velocity curve with a narrow velocity range at each time point. Maximum velocity is measured as shown. The VTI is measured by tracing the modal velocity (middle of the dense signal)

Pitfalls of the Continuity Equation

1. Depends on the variability in each of the three measurements, including both the variability in acquiring the data and variability in measuring the recorded data.

2. AS jet and LVOT velocity measurements - intra- and inter-observer variability (3–4%)

3. The measurement variability for LVOT diameter ranges from 5% to 8%.

4. When trans-thoracic images are not adequate for the measurement of LVOT diameter then TEE used.

Pitfalls of the continuity Equation When subaortic flow velocities are abnormal, for

example, with dynamic subaortic obstruction or a subaortic membrane, SV calculations at this site are not accurate.

Another limitation of valve area as a measure of stenosis severity is the observed changes in valve area with changes in flow rate.

In adults with AS and normal LV function, the effects of flow rate are minimal and resting effective valve area calculations are accurate.

This effect may be significant when concurrent LV dysfunction results in decreased cusp opening and a small effective orifice area even though severe stenosis is not present.

ALTERNATE MEASURES OF STENOSIS SEVERITY

(Level 2 EAE/ASE Recommendations )

Considering the ratio of LVOT to aortic jet VTI is nearly identical to the ratio of the LVOT to aortic jet maximum velocity.

AVA= CSA LVOT×VLVOT / VAV

Less well accepted because results are more variable than using VTIs in the equation.

Simplified continuity equation

Velocity ratio

Another approach to reducing error related to LVOT diameter measurements is removing CSA from the simplified continuity equation.

This dimensionless velocity ratio expresses the size of the valvular effective area as a proportion of the CSA of the LVOT.

Velocity ratio= VLVOT/VAV

In the absence of valve stenosis, the velocity ratio approaches 1, with smaller numbers indicating more severe stenosis.

Aortic valve area -Planimetry

Planimetry may be an acceptable alternative when Doppler estimation of flow velocities is unreliable

Planimetry may be inaccurate when valve calcification causes shadows or reverberations limiting identification of the orifice

Doppler-derived mean-valve area correlated better with maximal anatomic area than with mean-anatomic area.

Marie Arsenault, et al. J. Am. Coll. Cardiol. 1998;32;1931-1937

Planimetered Aortic VAvle

Aortic valve area - Planimetry

EXPERIMENTAL DESCRIPTORS OF STENOSIS SEVERITY

(Level 3 EAE/ASE Recommendations -not recommended for routine clinical use)

Valve resistance

Relatively flow-independent measure of stenosis severity

Depends on the ratio of mean pressure gradient and mean flow rate

Resistance = (ΔPmean /Qmean) × 1333

There is a close relationship between aortic valve resistance and valve area

The advantage over continuity equation not established

Left ventricular stroke work loss

Left ventricle expends work during systole to keep the aortic valve open and to eject blood into the aorta

SWL(%) = (100×ΔPmean)/ ΔPmean+SBP

A cutoff value more than 25% effectively discriminated between patients experiencing a good and poor outcome.

Kristian Wachtell. Euro Heart J.Suppl. (2008) 10 ( E), E16–E22

Energy loss index Damien Garcia.et al. Circulation. 2000;101:765-771.

Fluid energy loss across stenotic aortic valves is influenced by factors other than the valve effective orifice area .

An experimental model was designed to measure EOA and energy loss in 2 fixed stenoses and 7 bioprosthetic valves for different flow rates and 2 different aortic sizes (25 and 38 mm).

EOA and energy loss is influenced by both flow rate and AA and that the energy loss is systematically higher (15±2%) in the large aorta.

Damien Garcia.et al. Circulation. 2000;101:765-771.

Energy loss index Damien Garcia.et al. Circulation. 2000;101:765-771.

Energy loss coefficient (EOA × AA)/(AA - EOA)

accurately predicted the energy loss.

It is more closely related to the increase in left ventricular workload than EOA.

To account for varying flow rates, the coefficient was indexed for body surface area in a retrospective study of 138 patients with moderate or severe aortic stenosis.

The energy loss index measured by Doppler echocardiography was superior to the EOA in predicting the end points

An energy loss index ≤0.52 cm2/m2 was the best predictor of diverse outcomes (positive predictive value of 67%).

Classification of AS severity (a ESC & b AHA/ACC Guidelines)

Aortic

SclerosisMild Moderate Sever

e

Aortic jet velocity (m/s)

≤ 2.5 m/s 2.6 -2.9 3.0 - 4 > 4

Mean gradient (mm Hg)

< 20b(<30a)

20 – 40b (30 -50a)

> 40

AVA (cm²) > 1.5 1.0 - 1.5 < 1.0

Indexed AVA (cm²/m²)

> 0.85 0.60 – 0.85 < 0.6

Velocity ratio > 0.50 0.25 – 0.50 < 0.25

Effects of concurrent conditions

ASSOCIATED LV SYSTOLIC DYSFUNCTION

AS gradient becomes low, despite a small valve area- ‘low-flow low-gradient AS’

Defined as- 1. Effective orifice area 1.0 cm2

2. LV ejection fraction< 40% 3. Mean pressure gradient <30–40 mmHg

Dobutamine stress echo

Measures 1. contractile response

2. changes in aortic velocity, mean gradient, and valve area as flow rate increases

Helps to find out 1. Severe AS causing LV systolic

dysfunction2. Moderate AS with another cause of

LV dysfunction

Protocol

Low dose - 2.5 or 5 mg/kg/min with an incremental increase in the infusion every 3–5 min to a maximum dose of 10–20 mg/kg/min.

The infusion is stopped- 1. As soon as a positive result is obtained

2. Heart rate begins to rise more than 10–20 bpm over baseline or exceeds 100 bpm 3. Symptoms, blood pressure fall, or significant arrhythmias

RESULTS

AS velocity, MG, valve area, and EF preferably at each stage (to judge reliability of measurements) but at least at baseline and peak dose

An increase in valve area to a final valve area 1.0 cm2 suggests that stenosis is not severe.

Severe stenosis is suggested by an AS jet 4.0 or a mean gradient 40 mmHg provided that valve area does not exceed 1.0 cm2 at any flow rate.

Absence of contractile reserve (failure to increase SV or EF by 20%) is a predictor of a high surgical mortality and poor long-term outcome although valve replacement may improve LV function and outcome even in this subgroup.

LVH

Small ventricular cavity with thick walls and diastolic dysfunction

Small LV ejects a small SV so that, even when severe stenosis is present, the AS velocity and mean gradient may be lower

Continuity-equation valve area is accurate indexing valve area to body size

Hypertension

Associated in 35-40% HT increases LV pressure load may

cause changes in ejection fraction and flow

Mascherbauer J, Fuchs C, Stoiber M, Schima H, Pernicka E, Maurer G et al. Systemic pressure does not directly affect pressure gradient and valve area estimates in aortic stenosis in vitro. Eur Heart J 2008;29: 2049-57

presence of hypertension may therefore primarily affect flow and gradients but

less AVA measurement.

Aortic regurgitation

Severe AR accompanies AS, measures of AS severity remain accurate including maximum velocity, mean gradient, and valve area

High transaortic volume flow rate, maximum velocity, and mean gradient will be higher than expected for a given valve area.

Mitral valve disease

Severe MR, transaortic flow rate may be low resulting in a low gradient even when severe AS is present

A high-velocity MR jet may be mistaken for the AS jet as both are systolic signals directed away from the apex.

High cardiac outputRelatively high gradients in the

presence of mild or moderate AS The shape of the CWD spectrum

with a very early peak may help to quantify the severity correctly

Ascending aortaAortic root dilationCoarctation of aorta

Maximal aortic cusp separation (MACS) Vertical distance between right CC and

non CC during systole

M Mode- Aortic Stenosis

Aortic valve area MACS Measurement Predictive value

Normal AVA >2Cm2 Normal MACS >15mm

100%

AVA>1.0 > 12mm 96%

AVA< 0.75 < 8mm 97%

Gray area 8-12 mm …..

DeMaria A N et al. Circulation.Suppl II. 58:232,1978

THANK YOU

QUIZ

Question 1

A patient with severe aortic stenosis has MR. Which one of the following statements is incorrect?

1. The peak mitral regurgitation jet velocity is higher than the peak trans-aortic valve flow velocity.

2. The aortic transvalvular flow duration is shorter than the MR jet duration.

3. The LVOT flow duration is longer than the MR jet duration.

4. MR signal is not obtained in suprasternal window

Question 2

Which of the following is not a marker of severe aortic stenosis?1. Vmax across the Aortic valve is > 4m/s2. Calculated aortic valve area of 1.34

cm23. LVOT Vmx / AV Vmx ratio < 0.254. Mean gradient = 55 mmHg

Question 3

Which is not recommended in level A in assessing aortic stenosis

1. AS jet velocity2. Mean trans aortic gradient3. Valve area by continuity equation.4. Planimetry

Question 4

False about severe AS1. Mean gradient above 30 mm Hg2. Velocity ratio < 0.253. Indexed valve area < 0.6 cm/ m24. Peak velocity > 4m/sec

Question 5

At maximal dobutamine infusion, in an AS patient, the peak LVOT velocity increased from 50 to 90 cm / sec., while the peak transaortic valve velocity increased from 2 to 2.3 m/sec. The LVOT diameter is 2 cm. This study suggests that:

1. The baseline ejection fraction was < 20%.

2. There is significant AR. 3. AS is not severe. 4 LV motion did not improve.

Question 6

Which cannot be used for calculating area of aortic valve ?

1. MV annular diameter2. MV annular VTI3. AV VTI4. LVOT diameter

Question 7

False about Maximal aortic cusp separation? 1. MACS of normal aortic valve is >15 mm2. AVA <0.75 corresponds to MACS <8mm3. Vertical distance between left CC and

non CC during systole4. Gray area is 8-12mm

False about standard dobutamine stress echocardiography for evaluation of AS severity in setting of LV dysfunction

1 Uses low dose of dobutamine starting at 2.5 or 5ủg/kg/min

2 Maximum dose of dobutamine used is 10–20 ủg/kg/min

3 The infusion should be stopped when the heart rate begins to rise more than 10–20 bpm over baseline

4 Failure of LVEF to ↑ by 40% is a poor prognostic sign

Question 8

Question 9

Continuity equation obeys 1. Bernoulli`s principle2. Ohm`s law3. Law of conservation of energy4. Poiseuille`s law

Question 10

In a patient with aortic valve area of 0.6 sq cm(not a low flow low gradient AS) continuous wave Doppler velocity will be:

a) 1-2 m/secb) 2-3 m/secc) 3-4 m/secd) > 4 m/sec