The Role of Bicuspid Aortic Valve Hemodynamics in

BICUSPID AORTIC VALVE HEMODYNAMICS CONTRIBUTE TO ACUTE REMODELING IN PORCINE ASCENDING AORTAS Samantha K. Atkins, Kai Cao, Philippe Sucosky University of Notre Dame Department of Aerospace & Mechanical Engineering, University of Notre Dame, Notre Dame, IN, USA

THE BICUSPID AORTIC VALVE leftcoronary leaflet

rightcoronary leaflet

raphe

noncoronary leaflet

fused leaflet

noncoronary leaflet

Type-I bicuspid aortic valve (BAV)

Tricuspid aortic valve (TAV)

• BAV is the most common form of cardiac anomalies, affecting 1-2% of the population (Hoffman 2002; Basso 2004; Cozijnsen 2011) • BAV imparts the highest amount of disease compared to all other genetic heart diseases combined (Ward 2000; Siu & Silversides 2010)

Introduction

Hypothesis & Objective

Methods

Results

Conclusion & Limitation

Future Work

BAV IS LINKED TO AORTIC DISEASE BAV Risks Associated Risk

Chance

BAV Inheritance (1st Degree Relative)

10-17%

(1)

Aortic Valve Stenosis

40-53%

(2)

Aortic Valve Replacement

50-80%

(3)

Aortic Dilation

35-68%

(4)

Aortic Dissection

7-13%

(5)

Aortic Aneurysm

26-50%

(6)

Aortic Coarctation

20%

(7)

(1) Cripe et al. 2004 (2) Lewin & Otto 2005; Losenno et al. 2012 (3) Etz et al. 2001 (4) Braverman et al. 1996; Tzemos et al. 2008; Nistri et al. 2008; Beroukhim et al. 2006 (5) Yuan et al. 2010 (6) Mayo Clinic; Lewin & Otto 2005 (7) Warnes 2003 Introduction


Methods

Results


Future Work

BAV ASSOCIATED AORTIC DILATION IS ASYMMETRIC • The formation of aortic aneurysms is variable and there are currently no good predictors of aneurysm formation (Uretsky and Gillam, 2013) • Thinning of ascending aorta (AA) wall – Smooth muscle cell apoptosis (Della Corte et al. 2007)

– Elastic fiber degeneration (Antanas et al. 2011) – Decreased Fibrillin-1 (Tandros et al. 2009) – Increased MMP-2 and MMP-9 (Longo et al. 2002)

• Dilation is asymmetric in BAV patients and correlates with leaflet fusion patterns (Ikonomidis et al. 2012) • The most common Type-I BAV (L-R) is the “most aggressive” and dilation is localized to the disease-prone aortic convexity (Cotrufo et al. 2005; Della Corte et al.

Normal AA versus asymmetrically dilated AA at the convexity (Fedak et al. 2002)

2008; Ikonomidis et al. 2012)

Introduction


Methods

Results


Future Work

HEMODYNAMIC FORCES OF THE AORTA • Pressure: created by hydrostatic forces • Circumferential stretch: created by blood pulsatility and arterial compliance • Fluid Wall Shear Stress (WSS): created by the movement of blood; a product of shear rate at the wall and blood viscosity (µ)

Pressure

Introduction


Methods

Results


Future Work

BAV AORTOPATHY: CONTROVERSIAL ETIOLOGIES Hemodynamic Genetic Theory Theory •

Intrinsicvalve weakening of the leads aorticto Altered morphology altered hemodynamics that affect wall is caused by the same aortic remodeling congenital defect that causes BAV

BAV anatomic abnormality hemodynamic stress abnormalities

– vivo (Barker et al. 2012; Bauer et al. 2006; Bissell et al. – in Genetic mutations in NOTCH1, GATA5, 2013; Hope et al. 2008), ACTA2, and TGFBR2 have been – in vitro (Saikrishnan et al. 2012; Seaman et al. 2014) and investigated –

computational (Chandra et al. 2012; Nathan et al. 2011b)

studies reveal abnormal helical flow patterns and wall shear stress (WSS) overload on the convexity of BAV AAs.

structural/ hemodynamic changes

HEMODYNAMIC

signal transduction

THEORY OF

AORTIC DILATION

• The causality between • abnormal Currently, there is no and wall stress established genetic link aortic medial degeneration between thebeen BAV and aortic has not yet wall weakness demonstrated

Atkins et al., 2014 AORTIC Barker et al., 2012

DILATION

biological changes (inflammation, proteases and remodeling)

Seaman et al., 2014 Introduction


Methods

Results


Future Work

RESEARCH QUESTION, HYPOTHESIS AND OBJECTIVES • Question: Why does aortic dilation present asymmetrically in BAV patients? Does the hemodynamic theory provide clues? • Hypothesis: Abnormal wall shear stress (WSS) experienced by a BAV ascending aorta (AA) contributes to the development of acute aortic dilation. • Objective: To study the effect of BAV AA WSS on aortic tissue in the absence of any underlying aortic wall congenital defect, in order to isolate the direct effects of hemodynamics on aortic remodeling. Introduction


Methods

Results


Future Work

EX VIVO METHODOLOGY WSS WAVEFORMS •

Fluid Structure-Interaction (FSI) studies were used on a 3D aorta model reconstructed from CT images from the Visible Human Project aorta ascending aorta

descending aorta

Visible Human Project Image stack & Manual segmentation

Phantom reconstruction

3D aorta model Introduction


Methods

Results


Future Work

EX VIVO METHODOLOGY WSS WAVEFORMS • •

Fluid Structure-Interaction (FSI) studies were used on a 3D aorta model reconstructed from CT images from the Visible Human Project Boundary conditions using a TAV or BAV were imposed at the inlet of the AA

Introduction


Methods

Results


Future Work

EX VIVO METHODOLOGY WSS WAVEFORMS • • •

Fluid Structure-Interaction (FSI) studies were used on a 3D aorta model reconstructed from CT images from the Visible Human Project Boundary conditions using a TAV or BAV were imposed at the inlet of the AA WSS waveforms were extracted from the central region of the diseaseprone convexity

OSI TAV = 0.42 BAV = 0.00

Introduction


Methods

Results


Future Work

EX VIVO METHODOLOGY TISSUE CONDITIONING • WSS waveforms were programmed into a cone and plate bioreactor servo motor reservoir

servo drive

pump rotating cone pump

laptop computer culture medium tissue samples

perfusion system

mounting plate

pump

Introduction


Methods

pump

(Sucosky et al. 2008; Sun et al. 2011; Atkins et al. 2014) Results


Future Work

EX VIVO METHODOLOGY TISSUE ISOLATION AND CONDITIONING • •

Biopsy punches were sutured to theexposed tissue Normal A longitudinal The endothelium ascending cut of was aortas the made aorta dissected along was the from top of mounting plate porcine the aorta hearts attained7for a local Tissue biopsy punches mm in diameter were slaughterhouse taken from the disease-prone convexity with a custom biopsy punch intact aorta

mounting plate

endothelial surface exposed to flow

tissue samples location tissue samples sutured on plate

• Tissue was sterilely conditioned in the cone and plate bioreactor for 48 hours (Atkins et al. 2014) Introduction


Methods

Results


Future Work

EX VIVO METHODOLOGY TISSUE CONDITIONING TAV AA WSS Waveform

BAV AA WSS Waveform

(Atkins et al. 2014) Introduction


Methods

Results


Future Work

CULTURE CONDITIONS, BIOMARKERS, AND ASSAYS Biomarkers/structures Assessment Method Biological Endpoint Sample Group Culture Condition Cell nucleus, ECM Culture H&E staining Tissue structure and Duration components morphology Control DNA Fragments TAV AA WSS MMP-2, MMP-9 BAV AA WSS

0 hr

Fresh tissue TUNEL assay

48 hr

Immunohistochemistry Protease expression sites 10% FBS in DMEM with 1% antibiotics

Fibrillin-1

MMP-2, MMP-9, TIMP-1 and TIMP-2

Introduction


Cellular apoptosis

Western blot

Protease expression level

Zymography

Protease activity level

Immunohistochemistry

Microfibril location and organization

Western blot

Microfibril expression level

qPCR

Protease transcriptional expression level

Methods

Results


Future Work

TISSUE STRUCTURE AND CELL VIABILITY ARE NOT AFFECTED BY TAV AND BAV HEMODYNAMICS AFTER 48 HR

(Atkins et al. 2014)

Introduction


Methods

Results


Future Work

BAV HEMODYNAMICS PROMOTES MMP-2 AND MMP-9 EXPRESSION IN ASCENDING AORTIC TISSUE TAV AA WSS

BAV AA WSS

Fibrillin-1

MMP-9

MMP-2

Control

(Atkins et al. 2014) Introduction


Methods

Results


Future Work

BAV HEMODYNAMICS PROMOTES MMP-2 AND MMP-9 EXPRESSION IN ASCENDING AORTIC TISSUE Control TAV AA WSS

BAV AA WSS

pro MMP-2 active MMP-2 MMP-9 β-actin

* Indicates significance versus Fresh (control) p