Redesign of a Distal Protection Filter for Carotid Artery Stenting

University of PittsburghSenior Design – BioE 1160/1161

Sandeep DevabhakthuniChenara JohnsonDaphne Kontos

Perry Tiberio

April 18, 2005

Mentor: Ender Finol, PhD

Arterial Stenosis

• Narrowing of carotid arterial walls due to plaque build-up• Considered 3rd leading cause of

death - Stroke• New, less invasive treatment:

• Carotid Artery Angioplasty and Stenting

• Problem: Possible embolization to the brain resulting in a stroke.

• Solution: Embolic Protection Devices

Background

Filter Properties

• Neuroprotection (distal protection) filter

• Polyurethane material for the basket

• Nitinol tubing

• Nitinol

• Stainless steel

• 80-140µm pore size

Problem Statement

•Predicate devices include the FilterWire EX, AccuNet and Angioguard

•These filters are 80-90% efficient

•The goal of our design is to maximize emboli capture efficiency

AccuNet

FilterWire EX

Angioguard

Design Requirements

• 99% capture efficiency

• Lay flush with vessel lumen

• Biocompatible

• Durable

• Collapsible

• For insertion and retrieval

Economic Considerations and FDA Regulation

• Market Size:• $752M worldwide http://www.menet.umn.edu/~shayden/Neuro_report.pdf

• Distribution• Medical Supply Companies

• FDA Classification• Class II – Cardiovascular Diagnostic

Device

Quality System Considerations

• Manufacturability• Simple Design• Materials already used for other

medical purposes• Human Factors

• Easy to use for trained interventional cardiologists• To be determined through survey

• Biocompatible

• Incorporate the best features/materials from all current designs into our filter

• Implement a novel feature to improve design

Initial Design Considerations

• Ring

• Three struts

• Polyurethane basket

• 70-80µm pore size

• Skirt

Proposed Solution

• Ring• One Strut

• Extra Struts don’t assist in securing filter• Stainless steel wire• Nylon filter basket

• Nylon due to material restrictions• Polyimide tubing to enforce nitinol ring• Pore size of 70-80µm

• Captures smaller particles• Nylon skirt

Final Design

Prototype Fabrication

Shape nitinol into ring and reinforce

with polyimide tubing

Attach stainless steel wire guidewire

Prototype Fabrication

Dimensions of filter Basket

Outline filter on nylon sheet

Cut out pattern and put together

with polycyanoacrylate

Final Prototype

Intended Method of Use

• Collapse filter by pulling strut

• Insert percutaneously

• Deploy filter by releasing strut

• Pre-shaped to align 20° to vessel wall

• After procedure, retrieve into retrieval sheath

Experimental Methods Used to Test Device Performance

• Glycerin-water solution (9:16) in flow loop

• Insert filter into loop• Set peristaltic flow to 150 mL/min• Inject embolic beads• Run for 5 minutes• Weigh beads passed and collected by

filter

Schematic of Flow Loop

Insertion Point of Filter (one-

way valve)

Reservoir

Peristaltic Flow Pump

Length = 20 cmPoint of Filter Deployment

Glycerin/Water solution (9:16)

Inline filter

Insertion Point of particles

Data Analysis

• Embolic capture efficiency determined by:

• ezANOVA

• Between- and In-group comparison

• Student’s Paired t-test

100)___(

)1____(%

injectedparticlesmasstotal

filterinlineparticlesmassEfficiency

100)___(

)__(%

injectedparticlesmasstotal

filterparticlesmassEfficiency

Experimental Results

Particles Captured by Filter

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

0 2 4 6 8 10 12

Trials

Per

cen

t ca

ptu

red

Trial 1: 98% capture efficiency!

Experimental Results (cont.)

Modified Capture Efficiency

0.0

20.0

40.0

60.0

80.0

100.0

120.0

0 1 2 3 4 5 6

Trials

Per

cen

t ca

ptu

red

Filter Comparison Chart

AngioGuard AccuNet FilterWire Our Filter

Capture Efficiency

96.8 + 4.8 97.7 + 3.9 90.9 + 12.6 82.8 + 14.5*

*The modified capture efficiency data is presented here

Discussion

• Nitinol ring cracked during trial 2

• Bottom of filter tore during trial 6

• Filters are designed for one time use only

• Poor results due to:• Placement of filter• Retrieval mechanism

Competitive Analysis for Prototype I

• Strengths • Reduced pore size

• 74 microns compared to 80 – 120 micron range of filters currently on the market

• Skirt• Assists in maximizing capture

efficiency• Deeper basket

• Prevent loss during retrieval of filter

Competitive Analysis for Prototype I

• Weaknesses• Non-collapsible filter• Non functional delivery or retrieval

method• Not a 1:1 scale

Future

• Redesign flow loop to include:• Pressure Transducers• Latex Tubing

• Redesign a second prototype to include:• Develop a deployment/retrieval

mechanism• Use polyurethane as the filter basket

material• Use nitinol tubing

Acknowledgements

• Dr. Ender Finol• Sanna Gaspard• Mark Gartner• Special thanks to Drs. Hal Wrigley and

Linda Baker whose generous gift made this project work possible

• University of Pittsburgh, Department of Bioengineering

• Carnegie Mellon University