Aortic Stenosis

Question 1

What is the most common congenital abnormality of the AV? and how common is it?

Answer 1

Bicuspid AV

affects 0.5 - 2% population (3:1 male:female)

Question 2

List the fusion types of Bicuspid AV in order of prevelance.

Answer 2

1. Left + Right (71%)
2. Non + Right (15%)
3. Non + Left (3%)

Question 3

How are the types of BAV classified?

Answer 3

According to the number of raphe (fibrous ridge between leaflets)

• Type 0 : no raphe, true BAV (lat/AP)
• Type 1: 1 raphe (a R-L, b R -N, c L-N)
• Type 1: 2 raphe (functionally unicuspid)

Question 4

What is the pathophysiology of disease of BAV? And when does it present?

Answer 4

Secondary Calcification -> AS, AR or Both

onset of clinically significant symptoms 40 - 60 years of age

Question 5

What are BAV associated with?

Answer 5

Pathology of thoracic aorta - aneurysms of aortic root/ascending aorta and coarctation

Increased risk of Endocarditis

Question 6

How does the BAV appear on TOE views?

Answer 6

LAX : doming appearance of one or more cusps due to eccentric closure of the cusps (vs. prolapse)

SAX: elipitcal orifice (vs. normal triangular) due to unequal sized leaflets opening in systole

in diastole: may look like a normal leaflet closure line if calcified

Question 7

How do Quadricuspid and Unicuspid AV present?

Answer 7

Quadricuspid: incidental when presenting for AVR, associated with congenital coronary abnormalities

Unicuspid: present in childhood as AR/AS - have two raphes - asscoiated with aortic aneurysms

Question 8

What are the two main causes of AS?

Answer 8

1. Calcification; Bicuspid/Unicuspid Valves (earlier presentation 40-60yrs) or Tricuspid valves (70yrs +)
2. Rheumatic Disease: presents in younger patients (concomitant AR common) and often will have MV disease too

Question 9

What is the pathophysiology of AS?

Answer 9

Pressure Overload Problem

increaesed pressure in both end diastole and also that generated during systole

Question 10

What is the ACC/AHA Classification of AS?

Answer 10

Group A: at risk of AS (sclerosis)

Group B: Progressive AS

Group C: asymptomatic Severe AS ( normal or decreased LV systolic function)

Group D: symptomatic Severe AS
i) high grade stenosis
ii) low grade stenosis (dec. LVEF)
iii) low grade stenosis (nor. LVEF) [paradoxical low flow severe AS]

Question 11

What are the 3 main components of severe AS?

Answer 11

1. Peak Velocity > 4m/s
2. Mean Pressure > 40mmHg
3. Valve Area <1 cm-2

Question 12

When can calculated area be especially useful in AS?

Answer 12

If the peak velocity and mean gradients are lower than expected (can occur if decreased EF or SV)

Question 13

What are the indications for surgery in AS?

Answer 13

1. Symptomatic AS (D1)
2. Asymptomatic AS but LVEF <50% (C2)
3. Other Cardiac Disease

Question 14

What are the main differences in appearance on TOE of AS with Rheumatic Disease?

Answer 14

decreased calcification but increased commissural fusion

in normal/BAV/UAV: leaflet calcification of body/free edges of leaflet, may extend to intervalvular fibrosa/aMVL

Question 15

What should be considered if increased transvalvular gradients are found but no valve pathology is found?

Answer 15

LVOT obstruction

Question 16

What may be observed if there is dilation of the aortc root/ascending aorta with AS?

Answer 16

turbulent post-stenotic flow pattern

(BAV/UAV are associated with aortopathies)

Question 17

What other features should you observe for in AS?

Answer 17

1. Mitral Annular Calcification
2. Concentric LV Hypertrophy
3. Diastolic Dysfunction
4. Atherosclerosis of Descending Aorta

Question 18

What can occur if there is Concentric LV Hypertrophy in AS patients post repair?

Answer 18

If there is hypertrophy of the basal septum (‘septal knuckle’), this can cause dynamic LVOT obstruction post valve replacement

Question 19

What is the Bernoulli Eqn and why is it used?

Answer 19

The Bernoulli equation is used to estimate the pressure gradient across a valve:

ΔP = 4(V2)

where V is the peak velocity across the valve.

Question 20

What is a limitation of using CW doppler when quantifying AS?

Answer 20

If the Doppler beam is off axis, -> affects the velocity and pressure measurements

The obtained velocity measurement is then squared when using Bernoulli so the pressure estimations are even more affected

Question 21

What is the quoted acceptable beam divergence off axis?

Answer 21

if the beam is within 20% of the central flow then the underestimation will be < 6%

Question 22

In which situations may the velocity of flow in the LVOT be <1.5m/s? and what can be applied in this situation?

Answer 22

subvalvular membrane or a dynamic LVOT obstruction

An alteration of the Bernoulli equation is used

Question 23

When using the continuity equation to assess the AV Area - what assumption is made?

Answer 23

under conditions of CVS stability - it is assumed that the net forward SV in one part of the heart should equal that of another

Question 24

Using the continuity eqn - what compenents are solved for?

Answer 24

Stroke Volume = Valve Area x VTI

SV LVOT = SV AV

Question 25

What physics principle is the Continuity Equation based on?

Answer 25

based on the principle of conservation of mass

Question 26

What does VTI represent and how is it obtained?

Answer 26

The VTI represents the distance blood travels during one heartbeat obtained by tracing the Doppler waveform VTI = "Stroke Distance"

Question 27

What is the Double Envelope Technique?

Answer 27

the appearance of two Doppler envelopes: The first envelope is from PWD in the LVOT. The second envelope is from CWD at the aortic valve. Place the CW Doppler in the bright yellow low velocity region you can trace the VTI from both the AV and the LVOT from the same waveform

Question 28

When using the Continuity Eqn to calculate the AV area - what can be substituted instead of AV VTI?

Answer 28

Max Velocity

Question 29

Why does flow across a valve not affect the Continuity Eqn?

Answer 29

continuity equation accounts for changes in stroke volume, (it remains accurate regardless of flow) AV Area = LVOT Area x LVOT VTI/ AV VTI both the numerator (LVOT VTI) and denominator (Aortic VTI) change proportionally with flow If flow increases, both VTI values increase proportionally, keeping the AVA calculation stable. cross-sectional area of the stenotic valve does not change with flow, so AVA remains relatively stable valve area is a geometric measurement - unlike pressure gradients, which are dynamic measurements

Question 30

What is DI? and what does it assume?

Answer 30

Dimensionless Index - a simplified version of the continuity equationn It assumes that the LVOT area remains relatively constant over time it is a ratio of flow across LVOT: AV

Question 31

What is another term for Dimensionless Index?

Answer 31

DVI: "Doppler Velocity Index"

Question 32

When is DI particularly useful?

Answer 32

when the LVOT diameter is difficult to measure accurately, which can lead to errors in calculating the aortic valve area using the continuity equation)

Question 33

What is the formula for DI?

Answer 33

DI= VTI LVOT/ VTI AV ​ or DI= Vmax LVOT/ Vmax AV

Question 34

What DI represents AS?

Answer 34

DI < 0.25 (DI ratio should in health = 1)

Question 35

What are the advantages of DI?

Answer 35

1. Independent of Patient Size 2. Doesn't involve squaring values so decreased errors 3. Won't change if there is decreased SV through a valve (eg MR, muscular VSD, decreased systolic function)

Question 36

What are the two different types of Valve Orifice Area that can be measured?

Answer 36

1. Effective Orifice Area: measured by continuity equation - it is the jet of flow stream as it passes the valve 2. Anatomical Orificee Area: measured by planimetry or angiography EOA is often smaller than AOA

Question 37

How does flow affect transvalvular velocity and pressure measurements?

Answer 37

Flow (Cardiac Output) = Stroke Volume × Heart Rate Bernoulli Eqn often used to assess for Pressure Gradients and Velocities Higher transaortic systolic flow rates (increased stroke volume/heart rate (CO) or AR) = higher velocities and pressure gradients across a stenotic valve (for a given valve area)

Question 38

What is Low Flow/Low Gradient Aortic Stenosis?

Answer 38

Lower transaortic systolic flow rates (decreased CO or MR) = lower velocity and pressure measurements for a given valve area ( even if stenosis is still severe) 1. AVA Area (by continuity) <1cm2 2. Peak Velocity <4m/s 3. LV EF < 45-50% If low-flow, low-gradient aortic stenosis is suspected (e.g., in heart failure), assessing AVA using the continuity equation or DI is more reliable than pressure gradients.

Question 39

What are two possible explanations for Low Flow/Low Gradient Aortic Stenosis (PseudoAS)?

Answer 39

1. Low Flow due to AS 2. Moderate AS with another cause of decreased LFEF (eg. cardiomyopathy) the calculated AVA is low because the LV doesn't generate enough flow to fully open the AV leaflets

Question 40

How do you distinguish between low flow due to AS v.s moderate AS with low LVEF?

Answer 40

Dobutamine Stress Echo with dobutamine increase in ionotropy/flow -> an increase in velocity to >4m/s across the valve (and valve area remains constricted) or valve area with an increase to >1cm2 due to the increase in ionotrophy/flow Dobutamine stress echo is often used to increase flow and differentiate true severe AS from pseudo-severe AS (where gradients are low due to low cardiac output).

Question 41

What is Paradoxical Low Flow AS?

Answer 41

Low-Velocity Severe AS with a normal LVEF (group D3) In patients who have small hypertrophied LV and increased SVR (HTN) combination of low SV and high afterload -> low transvalvular velocity (<4m/s) despite the presence of severe AS

Question 42

How do you confirm the diagnosis of Paradoxical Low Flow AS?

Answer 42

1. low calculated AV area (<1 cm2 or <0.6 cm2/m2) 2. low SV index (<35ml/m2) then proceed to AV Replacement

Question 43

What is the Modified Gorlin Eqn? and when is it helpful?

Answer 43

Modified Gorlin Equation is an adaptation of the original Gorlin equation used to estimate valve area non-invasively using Doppler echocardiography (TOE), instead of invasive cardiac catheterization AVA = CO/(mean gradient)-1/2 AVA = CO/(peak gradient) Peak Gradient = CO/AVA Helpful in low-flow, low-gradient AS cases to differentiate true severe stenosis from pseudo-stenosis.

Question 44

What are the 2 types of Low-Flow, Low-Gradient Aortic Stenosis?

Answer 44

1. Classical LF-LG AS (with Reduced Ejection Fraction, EF) - Low flow: Stroke Volume Index (SVi) < 35 mL/m² - Low gradient: Mean transvalvular pressure gradient < 40 mmHg - Reduced LVEF (<50%) → Often due to heart failure with reduced EF (HFrEF) 2. Paradoxical LF-LG AS (with Preserved EF) - Low flow despite normal LVEF → - Often due to diastolic dysfunction or small LV cavity - Often seen in elderly patients with hypertrophic ventricles or restrictive filling patterns