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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.
Foin, 2012
Connector design with current platforms