1. Valve Durability Considerations: Fluid Dynamic Principles, Assessment Techniques, Predictors, and Minimum Standards
Jorge H. Jimenez, Ph.D.
Georgia Institute of Technology

2. Jorge H. Jimenez DISCLOSURES
Apica Cardiovascular Technologies - Founder

3. RISK ANALYSIS OF MI THERAPIES
Decades of experience from heart valve and stent industry
International standards panel in place
Standards are flexible as to conform to device specificity
Framework is based on Risk & Hazard Analysis
Risk evaluation ISO 14971

4. Risk Analysis Of MI Therapies
Node/Component
Description
Severity of risk
Procedure
Delivery
Anchoring
Verification
Correction
Structure
Loads
Dimensions
materials
Calcification
fatigue
Fluid
Functional characteristics
Abnormal patterns
Thrombosis/Thromboembolism
Blood damage
Tissue In-growth

5. Failure due to Fluid Mechanics
Stenosis
Leakage
Undesirable Flow field Characteristics
Loading of fluid on valve’s structure
Virchow’s Triad
Thrombosis and Thromboembolism

6. Stenosis & Leakage Stenosis Leakage Leaflet properties and suturing
Leaflet stiffening and calcification
Pannus overgrowth
Leakage
Frame over-expansion
Leaflet failure
Deployed geometry

7. High velocity forward jet
Flow Downstream of First Generations of Valves Flow Visualization and Laser Doppler Velocimetry
Ball and Cage Valve
Forward flow
m/s
EOA= 1.75 cm2
Vreg= 5.5 cm3/beat
for a 27 mm valve
Recirculation region
Forward flow jet
Tilting Disc Valve
Forward flow
m/s
EOA= 3.49 cm2
Vreg= 9.4 cm3/beat
for a 27 mm valve
Slow forward jet
High velocity forward jet
recirculation

8. Structural Leaflet Failure
Wear in coaptation areas
Frictional
Delamination
Calcification
Leaflet dislodgement at suture interface
Micro or macro orifices in tissue

9. Durability Testing
To demonstrate reasonable assurance that minimally invasive tissue valve substitutes will remain functional for million cycles
Target peak differential pressure
95 % or more of all the test cycles
At least 5% of each cycle
Some concerns:
Effects of excess leaflet tissue; folding leaflets
Interface between frame and leaflets
Definition of failure:
Structural
Regurgitation; Stenosis
????? (risk analysis)

10. Structural Failure Complete structural failure Collapsed frame
Partial failure of frame
Leaflet dislodgment or malcoaptation
Migration
Crack propagation
Long term failure

11. Testing for Structural Failure
Understanding the interaction between loads, materials and geometry
Design mechanical testing protocols to ensure structural integrity

12. LOADS
Do we really know the loads our devices will be subject to (animals, humans, bench)?
At level of annulus
On prosthetic valve leaflets
On stent superstructure by calcified native aortic valve and aorta
On calcified native leaflets and annulus
XXX

13. MATERIALS Raw material Post manufacturing Preconditioned
Standards
certification
Post manufacturing
Thermo-structural changes
Corrosion
Finish & micro-cracks
Preconditioned
Crimping
Cold working
Implanted material
Interaction with human body & environment
(ASTM F2516, Tolomeo, Duerig, and Tolomeo; SMST ’00)

14. Computational Models - FEA
Validated computational tools & models used to complement fatigue tests
Complex loading
Geometrical variations
Worst case scenario

15. Structural Testing
To demonstrate structural integrity million cycles – test to success
Dynamic failure mode tests (extended time or load):
Weak link
Failure Model validation
Definition of failure
Complete
Crack formation & propagation

16. Summary New minimally invasive technologies pose new challenges
70+ years of combined experience from heart valve and stent industry
Collaboration between Academia, Industry and FDA
Appropriate risk-based standards will result in safer technologies, improving patient welfare by getting to market needed technologies.