Hemodynamics of aortic stenosis

Dr Sajeer K TDepartment of Cardiology,

Govt. Medical College, Kozhikode

Aortic stenosis Etiology based on - level of obstruction to LVOT

- Supravalvular

- Valvular- Congenital AS- BAV ± calcification

- Rheumatic - Senile degenerative - Subvalvular

Pressure gradient across the AV ⇈es exponentially with ⇊ing AVA

# Severe AS: - small changes in AVA can lead to large changes in hemodynamics

Framework for how mechanical stress (σ) is transduced into pressure versus volume overload hypertrophy.

(Grossman W, Jones D, McLaurin LP: Wall stress and patterns of hypertrophy in the human left ventricle. J Clin Invest 1975; 53:332-341)

Compensatory Mechanisms

Chronic pressure overload concentric LV hypertrophy➨ increased wall thickness normal chamber size

⇈ed myocardial cell mass and ed interstitial fibrosis ⇈ - diastolic dysfunction

Women ➨ normal LV function small, thick walled LV concentric LVH diastolic dysfunction

Men ➨ eccentric LV hypertrophy excessive systolic wall stress systolic dysfunction & chamber dilation

Mild AS - intracardiac pressures & CO - normal

As the valve becomes more stenotic - unable to increase CO during exercise

Progressive narrowing of the valve - decreased SV and CO even at rest

Moderate to severe AS - patients may develop elevated filling pressures to compensate for the increase in LV EDP

Minority of patients LV systolic failure - further elevation in intracardiac pressures

Pulse wave

Valvular AS# Slow systolic rise# prominent anacortic notch# late peak

HOCM# rapid upstroke# absence of anacortic notch# early systolic dip# second peak in late systole

Supra valvular AS - pulse disparity (Coanda effect) - systolic pressure in the right arm > left arm. - relate to the tendency of a jet stream to adhere to a vessel wall selective streaming of blood into the innominate artery

Streaming of the jettoward the innominate, RCCA, and right SCA

Aortic Stenosis- severity

Mild Moderate Severe

Jet velocity (m/sec) <3.0 3.0-4.0 >4.0

Mean gradient (mm Hg) <25 25-40 >40

Valve area (cm2) >1.5 1.0-1.5 <1.0

Valve area index (cm2/m2) <0.6

Clinical Spectrum of Severe AS

# PLV1 exceeds PLV2 # VC – (2) - maximum velocity - site of minimal pressure# pressure recovery (3)# pressure P1 < P2

Factors involved in generation and interpretation of a pressure gradient

Pressure recovery - a source of error in the assessment of AS severity Severity of AS

1. pressure gradient across the valve or 2. effective orifice area (EOA) of the valve - preferable - less flow dependent

EOA measurement : 1. Doppler echocardiography (continuity equation) 2. Left heart catheterization ( Gorlin formula)

Discrepancies between Doppler and catheter measurements of EOA

Pressure recovery phenomenon

Valvulo-arterial impedance

SAP : systolic arterial pressure▲ Pmean : mean systolic transaortic gradientSVI : stroke volume index.

Values of Zva > 4.5 mm Hg. ml-1 .m -2 ➲ severe AS

“ cost in mmHg for each ml of blood indexed for BSA pumped by LV”

Zva = LV systolic pressure / SVI

Doppler : maximal pressure drop from the maximal velocity recorded at valve (EOA) level

Catheterization : measures the net gradient between the left ventricle and the ascending aorta

due to pressure recovery phenomenon: : net gradient recorded at catheterization is less than the maximum pressure gradient measured by Doppler (Ao < 3 cm)

: EOA by catheterization with Gorlin formula is higher than measured by Doppler

Doppler method : actual area occupied by flow at the valvular level

EOA by Gorlin formula: is a coefficient of the energy lost due to the stenosis

Energy loss coefficient (ELCo)

adjusts the Doppler EOA for the size of the aorta (AA)

ELCo = (EOA×AA) / (AA-EOA)

excellent agreement between catheter EOA and ELCo by Doppler

pressure recovery is a clinically relevant in patients with - moderate to severe AS (Doppler EOA between 0.8 - 1.2 cm2) - small aortas (diameter at the sinotubular junction < 30 mm)

AA : CSA of the aorta measured at 1 cm downstream of the STJ

Cut-off value for severe AS using the energy loss index < 0.55 cm2/ m2

Energy loss index

Energy loss index (ELI) = [EOA x AA / AA- EOA] BSA

1. Less flow dependent than gradient or peak velocity 2. Takes into account pressure recovery 3. Equivalent to EOA measured by catheter 4. Reflects true LV energy loss caused by stenosis5. Measured in patients with small aortas

Low-Flow, Low-Gradient Aortic StenosisWith Normal and Depressed LVEF

# Decreased EF (<40%) - Low Flow –Low Gradient AS # Normal EF ( ≥ 50%) - Paradoxical Low Flow –Low Gradient AS

⇊ in gradient ➨ in trans-valvular flow.⇊

Low-flow, Low-Gradient severe AS with decreased LVEF

# valve area <1 cm2

# mean aortic valve gradient < 40 mm Hg# ejection fraction <40%

# pseudo aortic stenosis ➨ medications that increase cardiac output will usually increase the calculated AVA

# Intravenous dobutamine - 5 μg/kg/min 20➔➔ μg/kg/min

# true severe aortic stenosis (1) a mean aortic valve gradient greater than 30 mm Hg (2) an aortic valve area ≤ 1.2 cm2

Effects of dobutamine infusion in patients with and without valvular AS

# Pseudo severe As Peak stress - MG < 30 mm Hg - EOA >1.0-1.2 cm2 - ab. in EOA> 0.3 cm2

Contractile reserve or flow reserve

# Definition: Increase in stroke volume of ≥ 20% above baseline

# Post AVR : lower peri-operative mortality (5% v/s 32%) ( n=136)

# Post AVR: mean improvement in In LVEF Improvement in NYHA class : similar in CR <20 or >20%

Paradoxical Low flow –low Gradient Severe AS:

- indexed AVA < 0.6 cm2/m2 - Gradient < 40 mmHg - EF > 50% - Stroke volume index (SVi) : < 35 mL/m2

Paradoxical Low flow –low Gradient Severe AS:

Increased global LV hemodynamic load -⇈ed Zva

Smaller and relatively thicker LV

⇊ed LV mid-wall radius shortening (pronounced intrinsic myocardial dysfunction)

lower LVEF

Paradoxical Low Flow –Low Gradient AS

Features :

Poor prognosis if treated medically rather than treated surgically

Physiopathology : paradoxical LF- AS despite preserved EF

Pronounced concentric LV remodelling and smaller LV cavity size ≈ restrictive physiology

# Decrease in SV is due to deficient ventricular filling# smaller LV cavity size # deficient ventricular emptying

# Intrinsic myocardial dysfunction causing EF lower than expected (50-60%)

# Prevalence increases with - older age - female gender - concomitant systemic HTN

Impact of AVR on Survival in Patients With Paradoxical LF-LG AS

Tarantini G, Covolo E, Razzolini R, et al. Valve replacement for severe aortic stenosis with low transvalvular gradient and left ventricular ejection fraction exceeding 0.50. The Annals of Thoracic Surgery, Volume 91(6), 1808–1815, 2011

Cardinal indications: - left ventricular failure, angina pectoris, or syncope.

Role of cardiac catheterization AS

What information can be obtained in AS ? - estimation of gradient - estimation of valve area - level of stenosis - valve resistance

Discrepancy between echo findings and patient symptoms

Methods of measuring a transvalvular gradient in AS

1. LV via transseptal, AO catheter retrograde above AO valve

2. LV retrograde with pressure wire, AO catheter retrograde above AO valve

3. LV retrograde with pigtail, AO catheter retrograde above AO valve

4. LV and AO retrograde with dual lumen pigtail

5. LV retrograde with pigtail, AO pressure from side arm of long sheath

6. LV retrograde with pigtail, AO pressure from side is of femoral sheath

7. LV retrograde with pigtail and ‘‘pullback’’ pressure from LV to AO

Simultaneous LV and central Aortic pressures in severe AS

Ideal method

METHOD EASE OF USE DISADVANTAGE

PULLBACK +++++ LEAST ACCURATE

FEMORAL SHEATH +++++ PRESSURE AMPLIFICATIONILIAC ARTERY STENOSIS

DOUBLE ARTERIAL PUNCTURE

+++ EXTRA VASCULAR ACCESS RISK

PIG TAIL- DOUBLE LUMEN

+++ DAMPING

TRANSEPTAL ++ RISK

Artifacts can result when a multiple-side-hole pigtail catheter is incompletely advanced into the LV chamber

Simultaneous measurement of aortic and FA pressure demonstrating peripheral amplification

Peripheral amplification# increase in peak systolic pressure and pulse pressure in peripheral arteries as compared to the central aorta

A. The tracings demonstrating the significant time delay for the pressure waveform to reach the RFA.

B. Realignment using tracing paper.

Peak aortic pressure and LV pressures are temporarily separated

Gradient described as # Peak-peak # Peak instantaneous # Mean gradient

Peak-peak gradient: - absolute difference between peak Ao systolic pressure and peak LVSP Peak instantaneous gradient: - max. gradient between Ao and LV at single point in time

Mean Gradient : - area b/n LV & Ao hemodynamic tracing - best quantify severity of AS

peak-to-peak gradient measured by catheterization is lower than the

peak instantaneous gradient measured by echo

Doppler data # Peak instantaneous gradient over time

Cath data # Peak to peak data

calculated mean pressure Gradients are comparable

Carabello Sign rise in arterial blood pressure during left heart catheter pullback in patients with severe aortic stenosis

Mechanism : related to partial obstruction of an already narrowed aortic orifice by the retrograde catheter & relief of this obstruction when the catheter is withdrawn

AVA<0.6cm2

Supra Valvular AS

Valvular AS

Sub valvular AS

Aorta pull back tracing- level of stenosis

1. Torricelli's law: flow across a round orifice F = AV CC

F = flow rate A = orifice area V = velocity of flow CC = coefficient of orifice contraction

Calculation of stenotic valve area

GORLIN FORMULA:

2. relates pressure gradient and velocity of flow - Torricelli's law

V = velocity of flowCv = coefficient of velocity - correcting for energy loss as pressure energy is converted to kinetic or velocity energy h = pressure gradient in cm H2O g = gravitational constant (980 cm/sec2) for converting cm H2O to units of pressure

A = F VCC

C = empirical constant accounting for CV and CC

h = mm Hg (rather than cm H2O)

GORLIN FORMULA:

C - empirical constant ( 0.85 for mitral valve, 1.0 for Aortic valve)

Flow (F) = is the total cardiac output expressed in terms of the seconds per minute during which there is actually forward flow across the valve.

F= CO (ml or cm3/min)

SEP (sec/min) x HR

cm3 x min Min x Sec

cm3 /sec

Hakki formula

Heart rate x SEP or DFP x constant ≈1

Mean GD

Automated computerized analysis

Hypertension + aortic stenosis

Concomitant hypertension mask the signs of AS severity

Evaluation of AS severity - performed when BP control is optimal

Progression of valvulo-arterial disease - pseudo-normalization of BP due to a reduction in SV

LV : faces a double pressure overload - develop symptoms at an earlier age

Conclusion

# diagnosis of severe AS should be based on results for AVA and indexed AVA rather than on gradients

# Paradoxical low flow-low gradient AS : better prognosis if treated surgically than medically

# Newer parameters for severity of AS - Energy loss index - Valvulo-arterial impedance

# Pressure recovery : Catheterization v/s Doppler gradient

References1. Braunwald's Heart Disease: A Textbook Of Cardiovascular Medicine 9th Edition2. Grossman's Cardiac Catheterization, Angiography, & Intervention, 7th Edition3. Otto And Bonow : Valvular Heart Diseases4. Kern- Hemodynamics 5. George A. Stouffer Cardiovascular Hemodynamics For The Clinician6. Yang-hemodynamics7. Morton G Kern-cardiac Catherization8. Kanu-chaterjee-text Book Of Cardiovascular Medicine9. Hemodynamic Rounds –Kern 10. Regosta- Hemodynamics11. Uptodate – aortic stenosis

Journals12. Jaac13. Circulation14. Can J Cardiol15. Europian Heart Journal16. Bmj Heart17. Chest Journal

Thank you

1. What is the calculated aortic valve area by Gorlins formula from the following parameters?

# CO-4400ml/min, # SEP- 0.5sec, # HR-50 beat/min # Mean aortic gradient =100mmHga) 0.7 cm2

b) 0.2 cm2

c) 0.9cm2

d) 0.4cm2

2. common pitfalls in the estimation of aortic valve area in the catheterization lab all except?

a) Peripheral amplificationb) Aortoiliac stenosisc) Aortic regurgitationd) Low gradient ASe) Alignment match

3. True regarding Carabello’s sign except?a) rise in pulse pressure by > 5 mm Hg when a catheter

is removed from the LVb) Phenomenon is seen in aortic valve area < 0.6cm2

c) Not seen when AVA> 0.7 cm2

d) Mechanism: additional occlusive effect of the catheter across the valve – decreasing aortic pressure

4. True about paradoxical low flow-low gradient AS except?

a) LVEF> 50%b) Indexed AVA <0.6cm2/m2 c) Stroke volume index< 35 ml/m2

d) Mean Gradient < 50 mmHg

5. In Dobutamine SE- pseudo severe AS is identified bya) Peak stress Mean gradient <30 mmHgb) Peak stress EOA > 0.6 cm2

c) absolute increase in EOA > 0.3 cm2

d) Stroke volume < 35 ml/m2

6. True about Paradoxical LF-LG severe AS except?a) More in femalesb) Prevalence decreases with agec) Prevalence Increases with concomitant systemic

HTNd) AVR (class II a recommendation ) is better than

Medical treatment

7. True regarding hypertension and aortic stenosis except?

a) Hypertension mask AS severityb) Pseudo normalization of blood pressure occursc) HTN + AS – vary late onset of AS symptomsd) LV faces more global LV hemodynamic load

8. True regarding contractile reserve except?a) Increase in stroke volume of ≥ 30% above baselineb) Lower contractile reserve –higher peri-operative

mortality after AVRc) mean improvement in In LVEF more in higher contractile reserve patients with severe AS after AVRd) Improvement in NYHA class- similar in high and low contractile reserve groups with severe AS after AVR

9. All are features of paradoxical low- flow , low -gradient AS except?

a) Increased global LV hemodynamic load - ed Z⇈ va

b) Smaller and relatively thicker LVc) intrinsic myocardial dysfunction d) Survival better after medical management than AVR

10. True about Energy loss index (ELI) except?a) Cut-off value for severe AS < 0.55 cm2/ m2

b) Less flow dependent than gradient or peak velocity c) Takes into account pressure recovery d) Equivalent to EOA measured by catheter e) Measured in patients with large aorta ( size >35 mm)

Valve resistance mean pressure gradient divided by the flow rate ratio.

UNIT = dyne-seconds cm−5

> 300 dyne-seconds cm−5 severe aortic stenosis➨

Hypertrophic cardiomyopathy

dynamic intraventricular pressure gradient

no systolic pressure gradient at rest gradient - provoked with : Valsalva maneuver : extra systole : systemic vasodilator (amyl nitrate) : inotropic stimulation

dynamic outflow obstruction characteristic arterial pressure ➨ waveform “spike-and-dome configuration

HOCM : spike-and- dome configuration of pulse wave

early spike rapid LV ejection by the hypercontractile myocardium➨

pressure dip & doming ➨ reflect the dynamic outflow obstruction

Valsalva maneuver : produces a marked increase in the gradient : change in the FA pressure waveform to a spike-and- dome configuration.

LV and FA pressure tracings in HCM

Brokenbrough-Braunwald-Morrow sign

Post PVC potentiation in HOCM PVC ➨ in intracavitary gradient ⇈ ➨⇈ed contractility (⇈ed Ca2+)# Post PVC beat is associated with a reduction in aortic systolic pressure and pulse pressure ≈ B-B-M sign