Analysis of neointimal coverage after silolimus-eluting stent implantation using optical coherence tomography.

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1 Analysis of neointimal coverage after silolimus-eluting stent implantation using optical coherence tomography. Division of Cardiology, Department of Internal Medicine, Fasculty of Medicine, Kinki University, Ohnohigashi Osakasayama Osaka, Japan Shinichiro Ikuta, Yoshitaka Iwanaga, Yoshihumi Nakauchi, Kenji Yamaji, Naoya Kobayashi, Hiroshi Yabushita, Takahiro Hayashi, Shunichi Miyazaki.

2 Background Drug Eluting Stent (DES) has been established to be effective in reducing restenosis after percutaneous coronary intervention (PCI). This benefit was due to its inhibitory effect on neointimal hyperplasia. However, this action of DES might induce a failure to complete neointimal coverage over the stent struts resulting in the crucial problem of the very late stent thrombosis.

3 Background (2) It is difficult to measure very thin neointimal thickness after stenting using intravascular ultrasound (IVUS), because its image resolution is approximately 100~200μm. On the other hand, optical coherence tomography (OCT) has potential advantage to evaluate neointimal thickness and the completeness of coverage because of the higher resolution (10μm) than IVUS.

4 Purpose Using OCT, we quantitatively measured the neointimal coverage at chronic stage after implantation of silolimuseluting stent (SES) and examined the difference of that after bare metal stent (BMS).

5 Patients Between April 2006 and February 2008, we enrolled 41 stents in 35 consecutive patients who underwent OCT examination with good quality of the image. SES; 33 stents in 28 patients BMS; 8 stents in 7 patients

6 Methods OCT imaging Pullback speed 1.0mm/s Measurement on the each slices The circumferential length of neointima was measured on the cross sectional plane in every 2mm from the distal edge of the stent. In the case of poor image, measurable cross sectional plane within 2 mm a point from the next image was substituted.

7 Representative case for the measurement of neointimal thickess. The vessel lumen boundary surface. Thickness of neointima The center of the stent strut

8 Classification of the neointimal coverage on the strut THK; The neointimal thickness is Thick (> 100μm). THN; The neointimal thickness is Thin( 10μm, 100μm) NON; Impossible to measure( <10μm) MAL; Strut not apposing the vessel wall (Malapposition) THK THN NON MAL

9 Example of OCT image of the SES THN; The neointima at the strut was 60μm. NON; The neointima at the strut was less than 10μm. MAL; Malapposition THK; The neointima at the strut was 200μm.

10 Representative case for measurement of the neointimal thickness on the struts of BMS All struts in the image were THK.

11 Expression of the percentage of the neointimal coverage. 1)The percentage of THK, THN, NON and MAL was calculated in each category divided by the whole number of struts and expressed as %THK, %THN, %NON and %MAL. 2)The percentage of NON was calculated in each stent and expressed as %NON/S.

12 Results: Patient characteristics SES BMS Number of patients 28 7 Number of stents 33 8 Male/Female 27/1 6/1 Age(years) 66.6 ± ± 6.4 Clinical diagnosis Stable AP, Silent ischemia 15 Unstable angina pectoris 2 (Hemodialysis patient ) 1 Acute myocardial infarction 5 Restenosis of BMS 5 Chronic total occlusion 5 Unstable angina pectoris 2 (Emergent procedure) (2) (7) Follow up period (days) ± ± 30.2

13 Comparison of the average neointimal thickness SES BMS Total stents 33 8 Measured slices Measured struts Average neointimal thickness (μm) 77.5 ± ±241.0

14 Comparison of the neointimal coverage %MAL 3.3% SES %THN 2.2% BMS %NON 19.3% %THK 25.2% %THN 52.3% %THK 97.8% Measured struts 3463 in SES. Measured struts 371 in BMS

15 Number of stents in which %NON/S was more than 5% SES N=33 %NON/S>5% N=26 < 5% N=5 0% N=2 BMS N=8 %NON/S=0% N=8

16 Number of stents including with MAL SES N=33 Malapposition(+) N=22 Malapposition(-) N=11 BMS N=8 Malapposition(-) N=8

17 The neointimal thickness on the struts of SES in the proximal, body and distal site. μm P<0.001 P<0.03 N=total 33 stents 3463 struts ± ± ±89.9 Proximal Body Mid Distal

18 The neointimal thickness on the struts of BMS in the proximal, body and distal site. μm 600 N=total 8 stents 371 struts ± ± ± Proximal Body Mid Distal

19 The malapposition struts of SES in the proximal, body and distal site. % P<0.001 P< % 3.4% 1.9% Proximal Body Mid Distal N=total 33 stents 3463 struts

20 Summary 1)The neointimal thickness of SES is thinner than that of BMS and 52% of all struts of SES were classified as THN. 2) Number of the stents in which neointima was judged as NON were 31/33 (93.9%) in SES. However no struts showed NON in BMS. 3)The neointimal thickness of SES were different depending on the distal, body and proximal site.

21 Conclusion The neointimal coverage of SES was insufficent in 22.6% (NON+MAL) of the struts and the thickness of neointima was different depending on the proximal or distal site of SES.