1. Walter Desmet, MD PhD, Christophe Dubois, MD PhD
The Absorb Bioresorbable Vascular Scaffold in coronary bifurcations: an in-vivo multi-modality imaging study
Johan Bennett, MD, Maarten Vanhaverbeke, MD, Nina Vanden Driessche, Tom Adriaenssens, MD PhD, Peter Sinnaeve, MD PhD,
Walter Desmet, MD PhD, Christophe Dubois, MD PhD
Department of Cardiovascular Diseases, University Hospitals Leuven, Leuven, Belgium
Department of Cardiovascular Sciences, Catholic University Leuven, Leuven Belgium
Financial Disclosures; J Bennett; Fee/Honoraria/Speaker’s Bureau for St-Jude Medical, Medtronic ; T Adriaenssens; Fee/Honoraria/Speaker’s Bureau for St-Jude Medical; P Sinnaeve; Fee/Honoraria/Speaker’s Bureau for Abbott, Cordis; C Dubois Fee/Honoraria/Speaker’s Bureau for Medtronic, Boston Scientific and Edwards LifeSciences
Background
Bioresorbable scaffolds (BRS) represent a promising new technology that theoretically can eliminate the late and very late stent thrombosis observed after deployment of metal DESs because, at some point, the physical material that could potentially provide a nidus for a stent-related thrombotic event completely disappears. However, the Absorb BVS has yet to be evaluated in patients with planned treatment of true bifurcation lesions because, unlike a metal stent, this polymeric BVS can unravel when deployed beyond recommended diameter limits and there are concerns that the integrity of the scaffold may be compromised by common techniques required during 2 stent bifurcation techniques such as recrossing, proximal optimization and kissing balloon dilatations.
This in-vivo study sought to provide insights regarding the feasibility and safety of performing complex bifurcation techniques with the Absorb everolimus-eluting bioresorbable vascular scaffold (BVS, Abbott Vascular, Santa Clara, California).
Results (Table 1 + 2)
In all 20 procedures angiographic results were excellent with no evidence of dissection or SB compromise. Re-crossing through BVS struts with guidewires was always successful and subsequent crossing with balloons and a second BVS (only in TAP + culotte procedures) was smooth. Provisional stenting (n=5) optimally opened the SB ostium without deforming the MV BVS. On OCT there was no malapposition in the MV and micro-CT revealed good SB aperture and a single connector fracture was present in the MV in 1 of the 5 cases (fig 1). Modified T stenting (fig 3, SB stented first, n=5) and TAP stenting (fig 4, MV stented first, n=5) resulted in complete coverage of the SB ostium and carina. Both techniques resulted in minimal double-strut layers at the carina and at the proximal SB ostium on OCT with no significant malapposition. On Micro-CT, no strut fractures were present following modified T stenting (fig 5), whilst in 3 out of 5 TAP procedures single strut fractures were noted, these did not cause luminal compromise. Culotte stenting (n=5) resulted in complete coverage of the bifurcation with an extensive proximal segment of double-layered scaffold struts. In 3 of the 5 culotte procedures, OCT revealed significant malapposition at the level of the bifurcation (fig 2). On micro-CT there was distortion of MV and SB scaffolds at the level of the bifurcation with single strut fractures present in all 5 cases affecting the MV BVS. These fractures did not cause luminal compromise though did increase the aperture between subsequent hoops. .
Methods
The study protocol was evaluated and approved by the ethical board for animal research of the University of Leuven. The experiments were performed in an in-vivo rabbit non-diseased aorta-iliac bifurcation model. Under general anaethesia (Xylazine and Ketamine), 20 New Zealand adult white rabbits (weight kg) underwent bifurcation interventions of the aorta-iliac bifurcation. Arterial access was achieved by denuding the carotid artery and introducing a long 6Fr sheath to the distal descending aorta. Absorb Everolimus-eluting BVS version 1.1 (3.0x24 mm) were implanted in single or 2-stent strategies. Optical coherence tomography (OCT) pullbacks were recorded in vivo using the IlumienTM IVOCT system and DragonflyTM catheters or the Optis system with DragonFly Duo catheters (St Jude Medical, St Paul, MN, USA). All images were stored for off-line analysis.
Following the completion of the bifurcation procedure and OCT examinations, the animal was sacrificed and the aorta-iliac bifurcation was dissected out and stored in 4% formol. Thereafter, micro-computed tomography (micro-CT) was performed using the SkyScan 1076 in-vivo micro-CT ( SkyScan/Bruker-microCT, Kontich, Belgium). The following bifurcation techniques were investigated: provisional stenting with final mini-kiss balloon post-dilatation (FKBD, n=5), modified T stenting with mini-FKBD (n=5), Culotte with mini-FKBD (n=5) and T-and Protrusion with mini-FKBD (n=5). Proximal Optimisation Technique (POT) was always performed using 3.5 mm NC balloons to 16 atm.
Figure 3
Figure 4
OCT images after Modified-T (fig 3) and TAP (fig 4) procedures
 Table 1: Procedure end OCT analysis
PROVISIONAL
(n=5)
MOD T
TAP
CULOTTE
Procedure succes
100%
Device succes
OCT assessment
Scaffold CSA (mm2)
Prox MV
10.1 ± 0.6
10.7 ± 2.0
10.9 ± 1.2
11.2 ± 0.2
Ostial distal MV
7.9 ± 1.0
8.1 ± 1.0
7.5 ± 0.5
8.4 ± 0.8
Ostial SB
8.3 ± 2.3
7.9 ± 0.4
8.2 ± 1.0
7.4 ± 3.1
Scaffold mean CSD (mm)
3.6 ± 0.1
3.7 ± 0.4
3.7 ± 0.2
3.8 ± 0.0
3.2 ± 0.1
3.2 ± 0.2
3.1 ± 0.1
3.3 ± 0.2
3.3 ± 0.5
Complete coverage bifurcation -
4/5
5/5
Malappostion
1/5
0/5
Distal MV SB
Bifurcation
MV scaffold
3/5
SB scaffold
Both
- Visible strut fracture
 Table 2:
Micro-CT analysis
PROVISIONAL
(n=5)
MOD T
TAP
CULOTTE
1. Proximal MV scaffold
- Strut fracture/elongation
0/5
2. Distal MV scaffold
3. SB scaffold
n/a
4. Bifurcation (POC) zone
- Multiple strut fractures
- Single strut fracture
1/5
3/5
5/5
MV scaffold
2/5
4/5
- Hoop -
- Connector
SB scaffold
- Luminal compromise
 1/5
Figure 5: 3D micro-CT reconstruction of Modified-T procedure
Conclusion
In this non-diseased in-vivo aorto-iliac bifurcation model, it was feasible to perform complex bifurcation stenting using Absorb BVS with excellent angiographic results. Provisional stenting of the main vessel with additional TAP stenting whenever needed seems a reasonable standard approach for most bifurcation lesions. Whenever a 2-stent technique is planned from the outset, modified T-stenting was the most promising with no evidence of significant malapposition or scaffold disruption on OCT and micro-CT, respectively. Finally, culotte stenting frequently caused significant malapposition, scaffold distortion and single strut fractures, the clinical impact of which is unknown.  
Figure 1
Figure 2
OCT images after provisional (fig 1) and Culotte (fig 2) procedures