TREATMENT FOR HYPOPLASTIC LEFT HEART SYNDROME: EFFECT OF REVERSE - - PowerPoint PPT Presentation

University of Central Florida Department of Mechanical and Aerospace Engineering Orlando, FL USA In Collaboration with: The Heart Center at Arnold Palmer Hospital for Children Orlando, FL USA and Sick Kids, Toronto, Canada

A MULTI-SCALE CFD ANALYSIS OF THE HYBRID NORWOOD PALLIATIVE TREATMENT FOR HYPOPLASTIC LEFT HEART SYNDROME: EFFECT OF REVERSE BLALOCK-TAUSSING SHUNT DIAMETER

Andres Ceballos, Eduardo A. Divo, I. Ricardo Argueta-Morales , Christopher Caldarone, Alain J. Kassab and William M. DeCampli

Background

HLHS Anatomy



Hypoplastic left heart syndrome (HLHS) is a complex cardiac malformation in neonates suffering from congenital heart disease.



1 in 5000 infants with HLHS are born each year.



The Norwood is the most commonly widely implemented first stage palliative treatment of HLHS.



Despite improvements in surgical techniques, the mortality rate in early post-

• perative palliation is 25%.

Background

Hybrid Norwood Anatomy

Avoids:

• Cardiopulmonary

bypass

• Cardioplegic and

circulatory arrest Procedure:

• Stenting of the ductus

arteriosus

• Branched pulmonary

artery banding

• Baloon atrial septostomy

Background

Hybrid Norwood Anatomy with reverse BT shunt

• Immediate or delayed
• bstruction in the aortic isthmus

after stent deployment may

• ccur
• The reverse BT shunt my

prevent myocardial and cerebral ischemia due to stenosis of the aortic isthmus

• HN with reverse BT

hemodynamics are complex

 Create a representative or patient-specific anatomical

model of the Hybrid Norwood circulation.

 Develop a multi-scale CFD model that accurately

represents the local and global hemodynamics.

 Study the hemodynamic effects on major arterial

perfusion of various degrees of distal aortic arch

• bstruction proximal to the ductus arteriosus stenting, as

well as the effects of shunt diameter.

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 Below is a representative 3D model of the Hybrid

Norwood anatomy with reverse BT-shunt (RBTS).

Subclavian arteries Carotid arteries Reverse BT-shunt Ductus Arteriosus Pulmonary arteries Coronary arteries

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Discrete Stenosis Model

 Two levels of stenosis were modeled to examine the

effect of distal arch obstruction on the hemodynamics.

Severe Obstruction (90% Reduction in Lumen) Moderate Obstruction (70% Reduction in Lumen)

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Six Anatomical CAD Models

 Twelve anatomical models

were analyzed: 1) Nominal 2-4) Nominal + 3, 3.5, 4mm RBTS 5) Stenosis 90% 6-8) Stenosis 90% + 3, 3.5, 4mm RBTS 9) Stenosis 70% 10-12) Stenosis 70% + 3, 3.5,4mm RBTS

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Banded Pulmonary Pulmonary Root Right Coronary

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Sever Stenosis

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• Blood was modeled as Newtonian and incompressible, with typical density

and viscosity values of ρ=1060 kg/m3 and μ=0.004 Pa-s.

• An unsteady, implicit Navier-Stokes equations solver STARCCM+ (k-

Epsilon Turb.) 𝛼 ∙ 𝑊 = 0 𝑏𝑜𝑒 𝜍 𝜖𝑊 𝜖𝑢 + 𝜍 𝑊 ∙ 𝛼 𝑊 = −𝛼𝑞 + 𝜈𝛼2𝑊

• 2nd order upwinding of convective derivatives
• A time step of Δt=4.62ms provided time-independent solution for a 130

bpm.

Lumped Parameter Model

Hybrid Norwood Circuit model

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Coupled ODE’s solved by 4th order explicit adaptive Runge-Kutta Fehlberg method

0.1 0.2 0.3 0.4 0.5 1 1.5

Elastance Function

ml mmHg

Erv t ( ) t

CFD Adjusted Parameters

Lumped Parameter Model

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A

Iteration: 1D circuit 3D CFD

1.

Initial circuit tuned to produce flow and pressure waveforms (match targeted cycle flow splits and pressure variations).

2.

Flow splits imposed to CFD from circuit.

3.

Generate CFD solution and CFD pressure wave forms.

4.

Modify the LPM resistances to match CFD pressure waveforms in the mean

• ver a cycle.

5.

Impose new flow splits from LPM circuit to CFD.

6.

Iterate until convergence (around 20 iterations) for ΔQ outlets < 10-2 

The circuit model imposes the flow-split boundary conditions at the outlets of the 3D model.



The input to the circuit model is the pulmonary root pressure waveform along with the targeted flow-rates at the AO, CA, … the outlets of the 3D CFD model.



Iteration is used to couple the two solutions.

Lumped Parameter model

Updated circuit parameters

Flow rate at branching

arteries (outlets)

Stagnation pressure

(inlet) 13

Coupling Scheme

 The current coupling scheme involves data

transfer between Starccm and the user code through file sharing.

Lumped-Parameter Model of the circulatory system

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Lumped-Parameter Model of the circulatory system Starccm controls the iterative process through Java code Output tables in Text format Input tables in Text format C-code performing the cardiac cycle, boundary conditions for Starccm

Results - Pressure Waveforms

Circuit constants were tuned to achieve representative pressure and flow waveforms and to balance Qp/Qs ~1 as well as target flow-rates to branching and coronary arteries. Right Ventricle

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Descending Aorta

Model

Outputs Catheter Data

 Nominal and Sten 90% cases, w/o RTBS

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Composite of driving pressures at outlets from the circuit model

100 87 74 61 48 35 100 35 100 35 100 35 0.5 1 1.36 0.5 1 1.36 0.5 1 1.36 0.5 1 1.36

Pressure (mmHg) Time (s) Nom Nom-RBTS Sten Sten-RBTS

RPA LPA LcorA RcorA LCA RCA LSA RSA DA P.Root

87 74 61 48 87 74 61 48 87 74 61 48

B

Model Outputs: Flow Comparison

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0.5 1 30 40 50 60 70 80

Nom Coronary Avg Pressure Nom-RBTS Coronary Avg Pressure Sten 90% Coronary Avg Pressure Sten 90%-RBTS Coronary Avg Pressure Sten 70% Coronary Avg Pressure Sten 70%-RBTS Coronary Avg Pressure Time (s) Pressure (mmHg)

0.5 1 1  1 2 3 4

Nom Coronary Flow Nom RBTS Coronary Flow Sten 90% Coronary Flow Sten 90%-RBTS Coronary Flow Sten 70% Coronary Flow Sten 70%-RBTS Coronary Flow Time (s) Volumetric Flow Rate (ml/s)

Model Outputs: Flow Comparison

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0.5 1 40 50 60 70 80

Nom Carotid Avg Press Nom-RBTS Carotid Avg Press Sten 90% Carotid Avg Press Sten 90%-RBTS Carotid Avg Press Sten 70% Carotid Avg Press Sten 70%-RBTS Carotid Avg Press Time (s) Pressure (mmHg)

0.5 1 5  5 10 15

Nom Carotid Flow Nom-RBTS Carotid Flow Sten 90% Carotid Flow Sten 90%-RBTS Carotid Flow Sten 70% Carotid Flow Sten 70%-RBTS Carotid Flow Time (s) Volumetric Flow Rate (ml/s)

Model Outputs: Flow Comparison

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Model Outputs: Flow Comparison

Nominal Severe Stenosis Severe Stenosis with rBT Shunt Nominal with rBT Shunt

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Model Outputs: Stenosis 90% + 4.0mm RBTS Flow Field

1 2 3 4

B

0.5 1 10  10 20 30

Nom-RBTS Shunt Flow Sten 90%-RBTS Shunt Flow Sten 70%-RBTS Shunt Flow Time (s) Volumetric Flow Rate (ml/s)

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Model Outputs: Stenosis 90% + 4.0mm RBTS Flow Field

Peak Systole Late Diastole

24 1 3 4

A

2

0.5 1 10  10 20 30

Nom-RBTS Shunt Flow Sten 90%-RBTS Shunt Flow Sten 70%-RBTS Shunt Flow Time (s) Volumetric Flow Rate (ml/s)

Model Outputs: Flow Comparison, Nominal + 4.0mm RBTS

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Model Outputs: Flow Comparison, Nominal + 4.0mm RBTS

Peak Systole Late Diastole

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Model Outputs: 3mm vs. 4.mm shunt

Peak Systole

3mm RBTS 4mm RBTS

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Model Outputs: 3mm vs. 4.mm shunt

Mid Diastole

3mm RBTS 4mm RBTS

WSS and OSI

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 Cycle averaged Wall Shear Stress (WSS)  Another useful metric is the Oscillatory Shear Index

(OSI), the cyclic departure of the wall shear stress vector from its predominant axial alignment

 OSI = 0 unidirectional WSS  OSI=0.5 purely oscillatory WSS

𝑃𝑇𝐽 = 1 2 1 − 𝜐𝑥

𝑈

𝑒𝑢 𝜐𝑥

𝑈

𝑒𝑢

WSS = 1 𝑈 𝜐𝑥

𝑈

𝑒𝑢

WSS Stenosis + RBTS

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4mm 3mm 3.5mm 4mm 3mm 3.5mm 90% + RBTS Nominal + RBTS

OSI Stenosis + RBTS

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90% + RBTS Nominal + RBTS 4mm 3mm 3.5mm 3.5mm 4mm 3mm

Summary remarks

 RBTS restores nominal flows and pressures to arch vessels

and coronaries in presence of severe and moderate arch

• bstruction

 RBTS reduces retrograde arch flow  RBTS does not exacerbate flow reversal in the carotids or

coronaries, increases Qp/Qs slightly

 Results suggest that: (1) the 4.0mm shunt shunt diameter

choice that may be problematic particularly when implemented prophylactically, and (2) the 3.0mm and 3.5mm shunts may be a more suitable alternative, with the latter being the preference since it provides similar hemodynamics at lower levels of wall shear stress. (3) RBTS may be problematic when implemented prophylactically – anticoagulation treatment

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Ongoing and Future Work

 Patient specific applications (with Fluid Structure

Interaction to account for vessel compliance).

 Aortic CT angiographic images of an HLHS

patient are used to generate a 3D model. Anterior View Posterior View Ductus Arteriosus Pulmonary Arteries

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Ongoing and Future Work Ongoing and Future Work

• Four main models

were created: (a). A nominal model, (b) a model with the reverse BT shunt, (c) a model with 90 percent stenosis , and (d) one with 90 percent stenosis and a reverse BT shunt.

• The models with the

reverse BT Shunt (b) and (d) have versions with a 3mm and a 3.5mm diameter shunt also (4 mm shunt shown)

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Ongoing and Future Work

Severe (90%) stenosis Nominal stenosis

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Ongoing and Future Work

Severe (90%) stenosis with 4.0mm RBTS

Ongoing and Future Work

Thank You

37

Thanks to the support of my colleagues and the American Heart Association, AHA 11GRNT7940011