The evolution of stent design for chronic iliac vein obstruction

Transcription

1 The evolution of stent design for chronic iliac vein obstruction Stephen Black Consultant Vascular Surgeon Clinical Lead for Venous and Lymphoedema Surgery Guys and St Thomas Hospital London

2 They

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4 Not Strong Enough Arterial stent Expanded with Venous Stent

5 Design Process 5

6 Designing is Cyclic and Iterative Design inputs, i.e. Clinical requirements drive the design and development process Feedback repeats the design process We as users need to provide feedback 6

7 Design Inputs Inputs and Requirements (Design Criteria) Ideally, requirements lead to a design centered in a Venn diagram An optimized design is achievable DESIGN #1 & #3 DESIGN REQUIREMENT #1 IDEAL OPTIMIZED DESIGN DESIGN #2 & #3 DESIGN #1 & #2 7

8 Design Constraints Design inputs have real world constraints Requirements and constraints often compete The ideal design is unachievable 8

9 Types of Requirements and Criteria Clinical Requirements (i.e. Safety, Patency) Engineering Requirements (Functionality, Specifications) Regulatory requirements Intellectual Property Manufacturability Development Cost Time to market 9

10 Intellectual Property Requirements Intellectual Property (IP) has become a requirement for medical devices to protect the product and company, especially in the United States According to US Patent & Trademark Office, the total number of medical device patents granted has increased by approx. 169% from 7,443 in 2009 to 19,992 in 2014

11 Regulatory Requirements MDD EEC: Council Directive concerning medical devices ISO 13485: Medical devices Quality management systems Requirements for regulatory purposes ISO 14971: Medical devices Application of risk management to medical devices 21 CFR 820: FDA Quality System Regulation ISO : Cardiovascular implants Part 2: Vascular stents ISO 10993: Biological evaluation of medical devices ISO 11135: Sterilization of heath care products FDA Guidance: Non-clinical engineering tests and recommended labeling for intravascular stents and associated delivery system 11

12 Clinical Requirements The purpose of the venous stent is to maintain an open lumen to allow flow, and reduce congestion and hypertension Effectiveness determined through patency rates Safety through low adverse events rates Improvement of venous symptomatic scores, i.e. CEAP and VCSS, can also be requirements 12

13 Engineering Requirements Crush Resistance Flexibility Radial Strength Deployment Scaffolding (Coverage) Diameters & Lengths The ideal stent has to be reasonably long and flexible, yet provide adequate radial strength to withstand opposing forces at the choke points. - Seshadri Raju, MD, FACS The ideal stent would be flexible with moderate radial force, no foreshortening, and allow for very precise and accurate placement. - Brooke Spencer, MD, FSIR Some desirable features are common to all stents, not just venous devices, and include precise deployment, good visibility, and flexibility of both a low profile delivery catheter and the deployed stent. However, certain attributes are more suited for venous applications, such as larger diameters ( 14 mm) and appropriate levels of radial force and crush resistance. - Mahmood K. Razavi, MD, FSIR Venous Stenting: Expectations and Reservations; Raju S, Razavi MK, Spencer B, Williams DM, Endovascular Today, July

14 Engineering Conflicts and Optimization Design Conflicts Strength vs Flexibility vs Foreshortening Scaffolding/Coverage vs Flexibility Crush Resistance and Radial Strength vs Deployment Each requirement is a lever that can be moved, however, it may affect and move other levers Optimization of a design is based on how all the levers are prioritized 14

15 Other Requirements/Constraints Manufacturability Without efficient manufacturing process, product cost can be high Without robust manufacturing process, defects and yields may jeopardize product quality Development Cost Increases with more design features and optimization Increases with design complexity Time to market Multi-year long process from concept to product release First-to-market typically establishes leadership and market share 15

16 It is principally about Radius

17 Stent Strength Chronic Outward Force: How much the stent pushes outward. Changes w diameter expansion. Often called Radial Force. Crush Resistance: How much the stent can resist a single load Radial Resistive Force: How much circumferential load a stent can resist

18 Hoop Strength (N) Radial Resistive Force 16mm Stent Radial Strength Hybrid Open Cell Closed Cell Braided Diameter (mm) Radial Resistive Force: How much circumferential load the stent can take

19 Stent Force (N) Stent Force (N) Stent Force (N) Stent Force (N) Crush Resistance Closed Cell Open Cell 1,4 0,7 1,2 0,6 1 0,5 0,8 0,6 Closed Cell - midpoint 0,4 0,3 Open Cell - midpoint 0,4 0,2 Closed Cell - endpoint 0,2 0,1 Open Cell - endpoint Extension (mm) Extension (mm) 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 Hybrid Extension (mm) Hybrid - midpoint Hybrid - endpoint 3 2,5 2 1,5 1 0,5 0 Braided Extension (mm) Braided - midpoint Braided - endpoint

20 Flexibility

21 Competitive Designs Closed Cell Open Cell Hybrid Braided Crush Resistance Flexibility Radial Strength Deployment Scaffolding Diameters & Lengths

22 Cook Zilva Vena

23 Bard Venovo

24 Sinous-Venous

25 Veniti Vici Strut Strut Ring Peak/Valley Strut Ring Cell Bridge Bridge 25

26 Sinus Obliquus

27 Others Medtronic Abre Gore -? (good platform with Tigris) Abbott -? Small start up companies

28 Patency Stent Choice Placement Errors Mistakes Technical Flow Inflow!!! CFV Clotting APLS Behcet s Anti-coagulation

29 Number of Patients Deep venous reconstruction programme Total patients seen 444 Total patients having intervention Acute DVT Chronic PTS

30 April 2012 and November 2015 TABLE 1

31 ACUTE PATEINTS 88% of CDT patients had a venous stent

32 CHRONIC PATEINTS Ulcer healed in 6/14 patients (43%)

33 Venous Stenting is Not New Significant body of clinical work Existing stents (off label) Wallstent Good success treating venous outflow obstruction (peer review publications) Current generation of stents in USA IDE trials IDE and available OUS VIVO Trial Zilver Vena (Cook Medical)- completed VIRTUS Trial VICI VENOUS STENT (VENITI, Inc.) - completed Venovo (Bard) - Startedrecruitment Abre (Medtronic) Next year April Sinus Venous/Obliquus (Optimed) No trial as yet Wallstent (BSCI) No trial Safety and efficacy of current designs

34 Conclusions The stent alone is not the panacea Know each device and technical issues Be honest in feedback and know this is just the beginning We need long term patient outcome data to support use We do not have data yet to know if this is durable