Current DES designs and expansion capacity testing

N. FOIN, MSc, PhD INTERNATIONAL CENTRE FOR CIRCULATORY HEALTH,

IMPERIAL COLLEGE LONDON

EBC COURSE 2012 February 2012

…anticipated completion date: 2026

construction of Sagrada Família basilica had commenced in 1882

Drug Eluting Stent Design

DES Stent

Mechanical Properties: -Radial Strength

-Flexibility/Deliverability -Fatigue -resistance to fractures

Drug Coating: Polymer Primer, Drug

Concentration+ Kinetics

Crowns and connectors design

Material: alloy, polymer, Strut thickness

Vessel healing response

Stent design: engineering terminology

XIENCE Prime 3.0 mm

Number of crowns, strut and connector structure define each stent design and its mechanical

characteristics

Rings

Connectors

Stent design: - Rings (hoops) provide radial support - Connectors hold rings together contributing to longitudinal stability

cell

Peaks (or Crowns)

Strut Thickness

Strut Length

(6 crowns, 3 cells)

Stent are designed with a succession of rings and connectors:

Stent terminology: workhorse/model designs

XIENCE 6 crowns design (3 cells, 2 peaks/cell)

XIENCE 9 crowns design (3 cells, 3 peaks/cell)

Stent design (crowns, cells) changes at different diameters Stents are manufactured in only 2 or 3 workhorse designs to cover the entire range of diameters

SMALL & MEDIUM VESSEL

LARGE VESSEL

2.25-3.0mm

3.5-4.0mm

Promus Element 2.75 Promus Element 3.0

model design is an important parameter for stent selection in bifurcation

Model design impact stent expansion result

MV deployment

KB

Cut-off between model designs is an important parameter for stent selection in bifurcation

MV deployment

KB

Foin, 2011

2.75

3.5

2.75

Element Xience Taxus Integrity BioMatrix Cypher 2.25 Very Small (2

connectors) Medium vessel workhorse (6 crowns, 3 connectors)

Small vessel workhorse (6 crowns, 2 connectors)

Small vessel workhorse (7crowns, 2 connectors*) *1.5 in Endeavor Resolute

Medium vessel workhorse (6 crowns, 2 connectors)

Medium vessel workhorse (6 crowns, 6 connectors) 2.50

Small vessel workhorse (8 crowns, 2 connectors) 2.75 Medium vessel

workhorse (9 crowns, 3 connectors) 3.00

Medium vessel workhorse (8 crowns, 2 connectors)

Medium/Large vessel workhorse (10 crowns, 2 connectors) 3.50

Large vessel (9 crowns, 3 connectors)

Large vessel (9 crowns, 3 connectors)

Large vessel (7 crowns, 7 connectors)

4.00 Large vessel (10 crowns, 2 connectors)

Large vessel (9 crowns, 3 connectors)

DES model designs

Companies rarely provide data on cut-off diameter between stent designs Max DES size 4.0mm except in Taxus for which up to 5.0mm diameter were provided Labeled DES expansion usually limited to 0.5-0.75 mm above largest nominal diameter

Foin, Sen, Di Mario, Davies. 2012

Stent Model design and Maximal expansion capacity

Small/Medium vessel

(6 crowns) 2.25-3.0mm

Large design (9 crowns) 3.5-4.0mm

XIENCE STENT

Large design (9 crowns)

Small vessel (6 crowns)

Data on expansion capacity beyond label use is not usually available

Expansion capacity depends on stent model design

XIENCE 6 crowns design

XIENCE 9 crowns design

Nominal = 3.0 mm

Post-dil at 4.0 mm

Post-dil at 5.0 mm, MLD = 4.4 mm

Nominal = 3.5 mm

Post-dil at 5.0 mm

Post-dil at 6.0mm (14atm), MLD = 5.7 mm

Overexpansion capacity testing

Straightening of the crowns, until physical limit Foin, 2012

Foin, Sen, Di Mario, Davies. 2012

Post-dilatation expansion and DES designs

Stent MLD (inner lumen) achieved after stepwise overexpansion and 2x final post-dilatation

4.0

5.0

6.0

Balloon Max. size

Minimal stent LD excluding struts Limited to 6.0 mm SC balloon at 14 ATM

Promus Element 2.75 Promus Element 3.0

In presence of a large diameter mismatch, we should look at workhorse design and maximal expansion capacity

Or upscale to a larger diameter (at low pressure)

MV deployment

KB

Impact for stent selection in bifurcation PCI

MV deployment

KB

Foin, 2011

Left-Main: impact of stent models

3.0 Xience Prime from LCx to LM

3.0 Xience Prime with 4.5mm proximal post dilation

3.5 (LWH) Xience Prime

with 4.5mm Prox. Dilatation

Culotte 3.0 + 3.5 Xience Prime

3.5

4.5

3.0

Change in cell opening diameter with overexpansion

Large cell opening diameter may impair drug concentration in the wall Potential risk of plaque prolapse

Changes in stent cell opening with overexpansion

Foin et al. 2012 submitted

Stent crowns deformations

with over-expansion

(largest design)

Stent maximal expansion capacity: a critical limiting factor for Left-Main treatment ?

OCT in LM after 4.0x38mm Resolute integrity and post-dil

with 5.0 NC balloon Incomplete stent apposition in LM despite several post-dilatations > 5.0

KB with 4.0/4.0 mm Stent MLD = 4.32 mm

Stent MLD = 4.70 mm

LM-Ostial LAD Pre Post 4.0x38mm stent LAD to LM and 5.0 post

4.0/4.0 KB M

Potential hazard with stent Over-Expansion

DES were not designed to be expanded beyond labeled use: little data is available from the industry on their performances/limitations above labeled use

Unknown stent response: loss in structural integrity, impaired drug delivery, increased metal fatigue and risk of stent fracture

Polymer damages can increase after extensive post-dilatations/over-expansion

Dogbone effect with protruding balloon > can cause foreshortening of the proximal stent rings

Strain on the vessel, risk of dissection ?

Risk of plaque prolapse ?

XIENCE Prime after Overexpansion

Off-Label use means…

…stepping into the unknown

Summary: Stent workhorse design

Stent model design determines stent Maximal Expansion Capacity.

Largest designs could be expanded at least > 5.4mm for all DES tested,

….but risk of reaching expansion limit with smaller designs

Therefore both DES platform and model design selection impact expansion

and apposition of the struts, particularly important in Left Main PCI

Limited data is available to document DES limitations in off label use

Risk of longitudinal compression at the ostium

Summary 1. Apposition in Left Main is critical

Foin et al. 2012

Summary 2: Knowing cut-off between model designs is critical

Stent min. inner MLD achieved after overexpansion and 2x final post-dilatation of each workhorse design

Minimal stent LD excluding struts Limited to 6.0 mm SC balloon at 14 ATM

Balloon Max. size

We welcome your questions

Thank you !

Acknowledgements:

E. Alegria, S. Sen, R. Petraco, S. Nijjer, C. Di Mario, D.P. Francis, J.E. Davies.

nicolas.foin@gmail.com

Foin, 2012

Connector design with current platforms