- Email: [email protected]
Retrospective Multicenter Comparison of S.M.A.R.T. CONTROL and MISAGO Stents in Treatment of Femoropopliteal Lesions
CLINICAL STUDY
Retrospective Multicenter Comparison of S.M.A.R.T. CONTROL and MISAGO Stents in Treatment of Femoropopliteal Lesions Kenji Suzuki, MD, Mitsuyoshi Takahara, MD, Yoshiaki Shintani, MD, Akiko Tanaka, MD, Yoshimitsu Soga, MD, Terutoshi Yamaoka, MD, Atsushi Tosaka, MD, Shinya Sasaki, MD, Daizo Kawasaki, MD, Taketsugu Tsuchiya, MD, Amane Kozuki, MD, and Osamu Iida, MD
ABSTRACT Purpose: To compare primary patency between MISAGO (Terumo Corporation, Tokyo, Japan) and S.M.A.R.T. CONTROL (Cordis Corporation, Miami Lakes, Florida), second-generation and first-generation nitinol stents, in femoropopliteal lesions. Materials and Methods: This multicenter, retrospective study included 240 cases with MISAGO stent implantation and 1,265 cases with S.M.A.R.T. stent implantation. The S.M.A.R.T. group had more Trans-Atlantic Inter-Society of Consensus (TASC) II class C/D lesions (53% vs 41%, P ¼ .001) and smaller reference vessel diameter (RVD) (5.3 mm ⫾ 0.9 vs 5.5 mm ⫾ 0.9, P o .001). Results: Kaplan-Meier estimates of 2-year primary patency after S.M.A.R.T. and MISAGO stent implantation were 67% and 55% (P ¼ .007). Interaction analysis revealed that TASC II classification and RVD had a significant influence on the association of MISAGO versus S.M.A.R.T. stents with the outcome. The study population was stratified according to TASC II classification and RVD, and MISAGO and S.M.A.R.T. stents were compared after propensity score matching. There was no significant difference in 2-year patency between the 2 stents in the subgroup with TASC II class A/B and RVD Z 5 mm (S.M.A.R.T. 82% ⫾ 4 vs MISAGO 74% ⫾ 5, P ¼ .480). MISAGO stents had lower primary patency than S.M.A.R.T. stents in cases with TASC II class C/D or RVD o 5 mm (S.M.A.R.T. 62% ⫾ 6 vs MISAGO 25% ⫾ 6, P ¼ .015). Conclusions: S.M.A.R.T. and MISAGO stents had similar patency in simple lesions, but MISAGO stents had lower patency than S.M.A.R.T. stents in more complex lesions.
ABBREVIATIONS CI = confidence interval, TASC = Trans-Atlantic Inter-Society of Consensus, TLR = target lesion revascularization
Femoropopliteal disease is the most common cause of symptomatic peripheral artery disease (1). Endovascular
therapy for femoropopliteal lesions is unsatisfactory in terms of postoperative vascular patency (2,3). Generally,
From the Department of Cardiology (K.S.), Saiseikai Central Hospital, Kyoto Prefectual University of Medicine, 1-4-17, Mita, Minato, Tokyo 108-0073, Japan; Department of Metabolic Medicine (M.T.), Osaka University Hospital, Osaka University, Osaka, Japan; Department of Cardiology (Y.Sh.), Shin-Koga Hospital, Kyushu University, Fukuoka, Japan; Cardiovascular Center (A.Ta.), Sendai Kousei Hospital, National Defense Medical College, Miyagi, Japan; Department of Cardiology (Y.So.), Kokura Memorial Hospital, Kochi University, Fukuoka, Japan; Department of Vascular Surgery (T.Y.), Matsuyama Red Cross Hospital, Kyushu University, Ehime, Japan; Department of Cardiology (A.To.), Kawakita General Hospital, Yamagachi University, Tokyo, Japan; Department of Cardiology (S.S.), Saka General Hospital, Gunma University, Miyagi, Japan; Department of Cardiology (K.D.), Morinomiya Hospital, Hyogo College of Medicine, Osaka, Japan; Department of Cardiology (T.T.), Kanazawa Medical University Hospital, Kanazawa Medical University,
Ishikawa, Japan; Department of Cardiology (A.K.), Saiseikai Nakatsu Hospital, Kobe University, Osaka, Japan; and Cardiovascular Division (O.I.), Kansai Rosai Hospital, Hyogo College of Medicine, Hyogo, Japan. Received November 15, 2015; final revision received and accepted May 29, 2016. Address correspondence to K.S.; E-mail: [email protected] M.T. receives personal fees from Johnson & Johnson K.K. Medical Company (Tokyo, Japan). None of the other authors have identified a conflict of interest. & SIR, 2016 J Vasc Interv Radiol 2016; XX:]]]–]]] http://dx.doi.org/10.1016/j.jvir.2016.05.042
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MISAGO vs S.M.A.R.T. Stent in Femoropopliteal Lesions
nitinol stents yield better patency rates than either plain balloon angioplasty or provisional stent deployment (4–7). Restenosis has been reported to occur in 21%– 31% of femoropopliteal vessels treated with a bare metal stent 1 year after implantation (8). New designs of nitinol stents have been introduced with the aim of improving long-term outcome (9–12). The MISAGO system (Terumo Corporation, Tokyo, Japan) is composed of a peripheral, nitinol, self-expanding stent and a rapidexchange delivery catheter. This system has been demonstrated to offer good conformability and resistance to fracture (10,11). The S.M.A.R.T. CONTROL stent (Cordis Corporation, Miami Lakes, Florida) is designed to deliver a self-expanding stent to femoropopliteal and iliac lesions (12). Although various other modalities have been applied to improve vessel patency, including drug-coated balloons (13–15), drug-eluting stents (16), and covered stents (17,18), atherectomy devices (19) and nitinol stents are widely available for femoropopliteal lesions. Moreover, comparative data on their efficacy are still few. The purpose of this study was to perform a retrospective comparison of multicenter data on the use of S.M.A.R.T. and MISAGO stents in the treatment of femoropopliteal lesions.
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Trial Registry, as recommended by the International Committee of Medical Journal Editors (no. UMIN000017658, REAL-SM registry: Retrospective multi-center comparison of S.M.A.R.T. and MISAGO stents in treatment of femoropopliteal lesions). Data from 10 cardiovascular centers on the use of MISAGO stents for femoropopliteal lesions between January 2013 and December 2013 were collected retrospectively. Among 277 patients who had the MISAGO stent deployed, 26 were excluded because of combined use with other stents, and 11 were excluded because of unavailable data. Consequently, 240 patients with MISAGO stent implantation were included in the analysis. Data on the S.M.A.R.T. stent were obtained from a retrospective analysis of a prospectively maintained multicenter database. Among 2,014 patients in whom a stent was successfully deployed for femoropopliteal lesions between January 2004 and December 2011, the S.M.A.R.T. stent was used in 1,495 patients. Among 1,495 patients in whom a S.M.A.R.T. stent was deployed, 230 were excluded because of unavailable data, leaving 1,265 patients to be included in the analysis. The baseline demographics are summarized in Table 1. All patients were required to attend the outpatient clinic of their hospital, and ankle-brachial index and duplex ultrasound were checked at 1, 3, 6, and 12 months and every 12 months thereafter for follow-up evaluation.
MATERIALS AND METHODS Study Design
Definitions
The study was approved by the ethics committee of each participating institution and registered with the University Hospital Medical Information Network-Clinical
Restenosis was defined as peak systolic velocity ratio 4 2.4 on duplex ultrasound, 4 50% stenosis on angiography or computed tomography, or a decrease
Table 1 . Baseline Characteristics of Overall Study Population
n Age, y Male sex Smoking Hypertension Dyslipidemia Diabetes mellitus
S.M.A.R.T.
MISAGO
1,265
240
P Value
73 ⫾ 9
72 ⫾ 9
.584
891 (70%) 800 (63%)
156 (65%) 151 (63%)
.108 .942
1,112 (88%)
194 (81%)
.005
910 (72%) 824 (65%)
187 (78%) 148 (62%)
.058 .304
Regular dialysis
301 (24%)
72 (30%)
.050
Chronic heart failure Critical limb ischemia
139 (11%) 402 (32%)
42 (18%) 83 (35%)
.007 .408
ABI before revascularization
0.60 ⫾ 0.22
0.60 ⫾ 0.21
.854
Aortoiliac lesion Poor below-the-knee runoff
225 (18%) 579 (46%)
44 (18%) 119 (50%)
.854 .290
TASC II class C/D
674 (53%)
99 (41%)
.001
Lesion length, cm Chronic total occlusion
14 ⫾ 9 699 (55%)
12 ⫾ 8 89 (37%)
o.001 o.001
Reference vessel diameter, mm
5.3 ⫾ 0.9
5.5 ⫾ 0.9
o.001
Note–Data are presented as mean ⫾ SD or number (%). Intergroup difference was tested by unpaired t-test for continuous variables and by Fisher exact test for dichotomous variables. ABI ¼ ankle-brachial index; TASC ¼ Trans-Atlantic Inter-Society of Consensus.
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of 0.2 in resting ankle-brachial index. The complete absence of a detectable signal was graded as complete occlusion. Radiographs were obtained for evaluation of stent fractures. Primary patency was defined as no restenosis or repeat revascularization in the treated vessel, and secondary patency was defined as reopening or redilation of a totally occluded or stenosed vessel by repeat revascularization. Calcification was assessed by fluoroscopic visualization of calcium deposits. A diagnosis of diabetes was based on the World Health Organization criteria (20). Hypertension was defined as systolic blood pressure Z 140 mm Hg or diastolic pressure Z 90 mm Hg. Dyslipidemia was defined as serum low-density lipoprotein cholesterol level Z 140 mg/dL, high-density lipoprotein cholesterol level r 40 mg/dL, or triglycerides Z 150 mg/dL. Poor cardiac function was defined as an ejection fraction of o 40%.
Statistical Analysis The data are presented as mean ⫾ SD for continuous variables and number (percentage) for discrete variables, if not otherwise described. A P value of o .05 was considered to be statistically significant. Primary patency, defined as freedom from restenosis after stent implantation, was determined by the Kaplan-Meier method, and intergroup differences were assessed by the log-rank test. The Cox proportional hazard regression model was used to investigate the association between the use of each type of stent and future risk of restenosis. The hazard ratio and 95% confidence interval (CI) were determined. Stratification analysis of the following background characteristics was also performed: sex, age, smoker, hypertension, dyslipidemia, diabetes mellitus, regular dialysis, chronic heart failure, critical limb ischemia, coexistence of aortoiliac lesion, poor runoff (defined as no or only 1 intact below-theknee vessel), Trans-Atlantic Inter-Society of Consensus (TASC) II classification, and reference vessel diameter. The P values for interactions between these variables and MISAGO versus S.M.A.R.T. stent implantation are also reported. Variables showing a significant interactive effect on restenosis with the use of each type of stent were used to stratify the study population to obtain a comparison of primary patency in each subgroup. To minimize intergroup differences in baseline characteristics, the comparison was performed after propensity score matching. The propensity score was obtained by using a logistic regression model in which confounders were included as explanatory variables. We selected the confounder variables that were expected to influence clinical decisions on stent selection and were available in our databases. The variables selected were sex, age, smoking, hypertension, dyslipidemia, diabetes mellitus, regular dialysis, chronic heart failure, critical limb ischemia, coexistence of an aortoiliac lesion, poor runoff, TASC II
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classification, reference vessel diameter, and stent diameter. We included all these variables in the matching, regardless of statistical significance of the association. One-to-one pair matching was performed using the nearest neighbor method without replacement. According to Austin’s recommendation (21), we matched to the logit of the propensity score ⫾ 0.2 SD. The development of the propensity score and the subsequent matching based on the score was performed separately in each subgroup. A paired analysis of intergroup differences was performed after matching. R version 3.1.0 (R Development Core Team, R Foundation for Statistical Computing, Vienna, Austria) was used for propensity score matching. All other analyses were performed with IBM SPSS Statistics for Windows version 22 (IBM Corporation, Armonk, New York).
RESULTS In the S.M.A.R.T. group, the mean follow-up period was 647 days ⫾ 513 (1.8 y ⫾ 1.4), and restenosis was observed in 387 cases. In the MISAGO group, the mean follow-up period was 369 days ⫾ 291 (1.0 y ⫾ 0.8), and restenosis was observed in 69 cases. The 1-year and 2year follow-up rates were 81% (1,019 of 1,265) and 62% (782 of 1,265) in the S.M.A.R.T. group and 68% (162 of 240) and 35% (85 of 240) in the MISAGO group. In the S.M.A.R.T. group, 228 cases (18%) of the 1,019 noncensored cases had restenosis at 1 year, and 332 cases (26%) of the 782 noncensored cases had restenosis at 2 years. In the MISAGO group, 29 cases (36%) of the 162 noncensored cases had restenosis at 1 year, and 68 cases (80%) of the 85 noncensored cases had restenosis at 2 years. A crude analysis revealed a significant intergroup difference in primary patency (P ¼ .007) (Fig 1). The stratification analyses were then performed (Fig 2). TASC II class C/D and reference vessel diameter o 5 mm showed a significant interaction effect on the association of MISAGO stent versus S.M. A.R.T. stent with restenosis. This finding suggested that the MISAGO stent was inferior to the S.M.A.R.T. stent in terms of primary patency in patients with TASC II class C/D or reference vessel diameter o 5 mm but comparable in other patients. Therefore, the study population was stratified into 1 of the following 2 subgroups for further analysis: (a) patients with TASC II class C/D or reference vessel diameter of o 5 mm or (b) patients with TASC II class A/B or reference vessel diameter of Z 5 mm. After stratification, propensity score matching was performed in each subgroup. Matching yielded 129 pairs in the subgroup with TASC II class A/B or reference vessel diameter Z 5 mm and 109 pairs in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (Fig 3a, b). No significant intergroup difference was observed in baseline characteristics after matching in the
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Figure 1. Primary patency after S.M.A.R.T. and MISAGO stent implantation in the overall unmatched population.
Figure 2. Association of MISAGO versus S.M.A.R.T. stent implantation with restenosis risk. Data are unadjusted hazard ratios for restenosis and their 95% CIs, obtained from the Cox proportional hazard regression analysis. P values are for individual interaction effects of MISAGO versus S.M.A.R.T. stent implantation and background characteristics.
2 subgroups (Table 2). There was also no significant difference in lesion length in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm (7 cm ⫾ 3 in the S.M.A.R.T. group and 7 cm ⫾ 4 in the MISAGO group, P ¼ .731) or the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (18 cm ⫾ 6 in the S.M.A.R.T. group and 17 cm ⫾ 8 in the MISAGO group, P ¼ .895). The ratio of reference vessel diameter to stent diameter (vessel-to-stent diameter ratio) also showed no significant difference in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm (0.87 ⫾ 0.11 in the S.M.A.R.T. group and 0.88 ⫾ 0.12 in the MISAGO group, P ¼ .736) or the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (0.84 ⫾ 0.12 in the S.M.A.R.T. group and 0.82 ⫾ 0.14 in the MISAGO group, P ¼ .468). Subsequently, primary patency was investigated in the matched population in each subgroup. In the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm, the S.M.A.R.T. group had a mean follow-up of 709 days ⫾ 543, with restenosis observed in 26 cases, whereas the MISAGO group had a mean follow-up of 445 days ⫾ 343, with restenosis observed in 24 cases. In contrast, in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm, the S.M.A.R.T. group had a mean follow-up of 599 days ⫾ 467, with restenosis observed in 35 cases, whereas the MISAGO group had a mean follow-up of 280 days ⫾ 182, with restenosis observed in 45 cases. As shown in Figure 4a, no significant difference was observed between MISAGO and S.M.A.R.T. stent implantation in the subgroup with TASC II class A/B and reference vessel
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Figure 3. Distribution of propensity scores in matched and unmatched populations with MISAGO versus S.M.A.R.T. stent implantation. (a) Distribution of propensity scores in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm. (b) Distribution of propensity scores in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm. The distribution of the score across the matched MISAGO and S.M.A.R.T. groups was quite similar, indicating that clinical probability (or propensity) to select the MISAGO versus S.M.A.R.T. stent was well matched between the 2 groups.
Table 2 . Baseline Characteristics of Matched Study Population TASC II Class A/B and Reference
TASC II class C/D or Reference
Diameter Z 5 mm
Diameter o 5 mm
S.M.A.R.T. (n ¼ 129) MISAGO (n ¼ 129) P Value S.M.A.R.T. (n ¼ 109) MISAGO (n ¼ 109) P Value Age, y Male sex
72 ⫾ 9 92 (71%)
72 ⫾ 9 94 (73%)
.555 .897
74 ⫾ 10 66 (61%)
73 ⫾ 9 62 (57%)
.105 .694
Smoking
79 (61%)
82 (64%)
.798
66 (61%)
68 (62%)
.897
Hypertension Dyslipidemia
104 (81%) 97 (75%)
104 (81%) 97 (75%)
1.000 1.000
93 (85%) 87 (80%)
89 (82%) 88 (81%)
.584 1.000
Diabetes mellitus
79 (61%)
75 (58%)
.699
71 (65%)
72 (66%)
1.000
Regular dialysis Chronic heart failure
35 (27%) 16 (12%)
36 (28%) 17 (13%)
1.000 1.000
41 (38%) 28 (26%)
35 (32%) 22 (21%)
.480 .532
Critical limb ischemia
43 (33%)
43 (33%)
1.000
41 (38%)
39 (36%)
.883
Aortoiliac lesion Poor below-the-knee runoff
24 (19%) 56 (43%)
25 (19%) 56 (43%)
1.000 1.000
14 (13%) 57 (52%)
17 (16%) 61 (56%)
.664 .643
TASC II class C/D
0 (0%)
0 (0%)
—
95 (87%)
97 (89%)
.832
Reference diameter o 5 mm
0 (0%)
0 (0%)
—
27 (25%)
32 (29%)
.511
Note–Data are presented as mean ⫾ SD or number (%). Intergroup difference was tested by paired t-test for continuous variables and by McNemar test for dichotomous variables. TASC ¼ Trans-Atlantic Inter-Society of Consensus.
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Figure 4. Primary patency after S.M.A.R.T. and MISAGO stent implantation in the matched population. (a) Primary patency in cases with TASC II class A/B and reference vessel diameter Z 5 mm. (b) Primary patency in cases with TASC II class C/D or reference vessel diameter o 5 mm.
diameter Z 5 mm (P ¼ .480). In contrast, MISAGO stent implantation yielded a significantly lower rate of primary patency than S.M.A.R.T. stent implantation in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (P ¼ .015) (Fig 4b). Similarly, the MISAGO group had a significantly higher risk for target lesion revascularization (TLR) compared with the S.M. A.R.T. group in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (P ¼ .022) but not in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm (P ¼ .273) (Fig 5a, b).
Stent Fracture In the overall population before matching, 76 cases of stent fracture were observed in the S.M.A.R.T. group, accounting for 5% of patients with S.M.A.R.T. stents. No stent fractures were observed in the MISAGO group. In the S.M.A.R.T. group, stent fracture was significantly associated with restenosis and TLR; the hazard ratios were calculated to be 1.88 (95% CI, 1.36–2.60, P o .001) for restenosis and 1.92 (95% CI, 1.36–2.68, P o .001) for TLR, respectively.
DISCUSSION In this retrospective multicenter study, 2-year patency was investigated in 2 types of nitinol stents. The results
revealed that the S.M.A.R.T. stent provided superior primary patency. Moreover, our stratification analysis showed that a TASC II class C/D lesion or reference vessel diameter of o 5 mm was more strongly associated with risk of stenosis with the MISAGO stent than with the S.M.A.R.T. stent. Numerous novel modalities have been used to treat femoropopliteal lesions. Studies on the use of drugcoated balloons in femoropopliteal interventions have shown that the rate of 6-month TLR were 4%–7% (13,15) in various subsets of femoropopliteal lesions. Covered stents (17) have also been used in cases of long diffuse femoropopliteal lesions, and a 1-year patency indicated 78.1%. A 1-year primary patency of 78% was demonstrated with use of atherectomy devices to treat infrainguinal lesions of up to 20 cm in length (18). Vessel recoil, dissection, and suboptimal results often occur in balloon angioplasty, and they are related to poor outcome (4). Graft thrombosis is another problem encountered with the use of covered stents (17). For these reasons, nitinol stents still play an important role in femoropopliteal interventions. Although the primary patency of nitinol stents showed no advantage over angioplasty in the treatment of short femoropopliteal lesions (22), their efficacy has been apparent in long lesions. The ABSOLUTE and RESILIENT trials repor-
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Figure 5. Freedom from TLR after S.M.A.R.T. and MISAGO stent implantation in the matched population. (a) Rate of freedom from TLR in cases with TASC II class A/B and reference vessel diameter Z 5 mm. (b) Rate of freedom from TLR in cases with TASC II class C/D or reference vessel diameter o 5 mm.
ted that nitinol stents yield superior patency to balloon angioplasty (4,5). Mean lesion length in the present study, which included severe diffuse lesions, was 15 cm. The MISAGO stent demonstrated good conformability and excellent resistance to stent fracture; thus, a special feature of the MISAGO stent is flexibility. Although a relatively high rate of stent fracture was reported with the S.M.A.R.T. stent (23), it does offer stronger radial force (24). In the present study, a primary patency of 86% at 1 year and 75% at 2 years was observed with the MISAGO stent in the TASC A/B and reference vessel diameter Z 5 mm subgroup. This result was consistent with results of the MISAGO 2 study (11). Taken together, it is suggested that the MISAGO stent offers relatively good patency in simple lesions. In the same way, the present results for the S.M.A.R.T. stent in the TASC A/B and reference vessel diameter Z 5 mm subgroup were similar to the results of the STROLL study (12). In simple lesions, 2-year primary patency showed no difference between the 2 types of stent. However, the present results differed between each type of stent in the TASC II class C/D or reference vessel diameter o 5 mm subgroup in that primary patency with the MISAGO was lower than that with the S.M.A.R.T. stent. These data suggest that the maintenance of vessel patency requires stronger radial force in diffuse, long
lesions. In general, femoropopliteal stents are exposed to bending, compression, and twisting secondary to repetitive flexion of the joint. More flexible stents were introduced because stent fracture was associated with poor patency (23). However, although flexibility is important, radial force may be even more important. It was reported that the minimal stent area was related to less primary patency (25). Subintimal angioplasty was performed in many femoropopliteal cases. Stent underexpansion was often observed in subintimal angioplasty. A flexible stent such as the MISAGO may need to perform at high pressure after dilation. Woven nitinol stents were shown to exhibit greater radial force and produce favorable results in popliteal lesions (26). Taken together, these results suggest that both strong radial force and high resistance to stent fracture are necessary requirements in femoropopliteal stents. This study had several limitations, which may have skewed the clinical outcomes. First, although a propensity matched analysis was performed, this was a retrospective and nonrandomized study with a large sample size. Second, the observation period in the MISAGO group was shorter than the observation period in the S. M.A.R.T. group because the MISAGO stent was clinically approved later than the S.M.A.R.T. stent. Third, the sample size was too small to investigate the cutoff point of reference vessel diameter in more detail. Fourth,
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the data on stent fracture were obtained only at the final follow-up evaluation. Fifth, this study had no data about overlap after balloon dilation or stent placement. Lastly, the observation period was longer for the S.M.A.R.T. group than for the MISAGO group, and the apparently high stent fracture rate in the S.M.A.R.T. group might be due to this longer observation duration. Therefore, the study was inconclusive regarding interstent comparison of stent fracture rates. In conclusion, the S.M.A.R.T. stent showed superior efficacy to the MISAGO stent in terms of 2-year patency. The difference between the 2 types of stent was more obvious in cases with TASC II class C/D or a reference vessel diameter o 5 mm.
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12. Gray WA, Feiring A, Cioppi M, et al. STROLL Study Investigators. S.M.A.R.T. self-expanding nitinol stent for the treatment of atherosclerotic lesions in the superficial femoral artery (STROLL): 1-year outcomes. J Vasc Interv Radiol 2015; 26:21–28. 13. Tepe G, Zeller T, Albrecht T, et al. Local delivery of paclitaxel to inhibit restenosis during angioplasty of the leg. N Engl J Med 2008; 358: 689–699. 14. Werk M, Langner S, Reinkensmeier B, et al. Inhibition of restenosis in femoropopliteal arteries: paclitaxel-coated versus uncoated balloon: femoral paclitaxel randomized pilot trial. Circulation 2008; 118: 1358–1365. 15. Stabile E, Virga V, Salemme L, et al. Drug-eluting balloon for treatment of superficial femoral artery in-stent restenosis. J Am Coll Cardiol 2012; 60:1739–1742. 16. Dake MD, Ansel GM, Jaff MR, et al. Sustained safety and effectiveness of paclitaxel-eluting stents for femoropopliteal lesions: 2-year follow-up from the Zilver PTX randomized and single-arm clinical studies. J Am Coll Cardiol 2013; 61:2417–2427. 17. Lammer J, Zeller T, Hausegger KA, et al. Heparin-bonded covered stents versus bare-metal stents for complex femoropopliteal artery lesions: the randomized VIASTAR trial (Viabahn Endoprosthesis With PROPATEN Bioactive Surface [VIA] Versus Bare Nitinol Stent in the Treatment of Long Lesions in Superficial Femoral Artery Occlusive Disease). J Am Coll Cardiol 2013; 62:1320–1327. 18. Saxon RR, Chervu A, Jones PA, et al. Heparin-bonded, expanded polytetrafluoroethylene-lined stent graft in the treatment of femoropopliteal artery disease: 1-year results of the VIPER (Viabahn Endoprosthesis with Heparin Bioactive Surface in the Treatment of Superficial Femoral Artery Obstructive Disease) trial. J Vasc Interv Radiol 2013; 24: 165–173. 19. McKinsey JF, Zeller T, Rocha-Singh KJ, et al. DEFINITIVE LE Investigators. Lower extremity revascularization using directional atherectomy: 12-month prospective results of the DEFINITIVE LE study. JACC Cardiovasc Interv 2014; 7:923–933. 20. World Health Organization. Definition and diagnosis of diabetes mellitus and intermediate hyperglycemia. Report of a WHO/IDF consultation. 2006. Available at: http://www.idf.org/webdata/docs/WHO_IDF_defini tion_diagnosis_of_diabetes.pdf. Accessed August 11 2016. 21. Austin PC. Optimal caliper widths for propensity-score matching when estimating differences in means and differences in proportions in observational studies. Pharm Stat 2011; 10:150–161. 22. Krankenberg H, Schluter M, Steinkamp HJ, et al. Nitinol stent implantation versus percutaneous transluminal angioplasty in superficial femoral artery lesions up to 10 cm in length: the Femoral Artery Stenting Trial (FAST). Circulation 2007; 116:285–292. 23. Scheinert D, Scheinert S, Sax J, et al. Prevalence and clinical impact of stent fractures after femoropopliteal stenting. J Am Coll Cardiol 2005; 45: 312–315. 24. Isayama H, Nakai Y, Toyokawa Y, et al. Measurement of radial and axial forces of biliary self-expandable metallic stents. Gastrointest Endosc 2009; 70:37–44. 25. Iida O, Takahara M, Soga Y, et al. 1-year results of the ZEPHYR Registry (Zilver PTX for the Femoral Artery and Proximal Popliteal Artery): predictors of restenosis. JACC Cardiovasc Interv 2015; 8:1105–1112. 26. Scheinert D, Werner M, Scheinert S, et al. Treatment of complex atherosclerotic popliteal artery disease with a new self-expanding interwoven nitinol stent 12-month results of the Leipzig SUPERA Popliteal Artery Stent Registry. J Am Coll Cardiol Interv 2013; 6:65–71.
Retrospective Multicenter Comparison of S.M.A.R.T. CONTROL and MISAGO Stents in Treatment of Femoropopliteal Lesions Kenji Suzuki, MD, Mitsuyoshi Takahara, MD, Yoshiaki Shintani, MD, Akiko Tanaka, MD, Yoshimitsu Soga, MD, Terutoshi Yamaoka, MD, Atsushi Tosaka, MD, Shinya Sasaki, MD, Daizo Kawasaki, MD, Taketsugu Tsuchiya, MD, Amane Kozuki, MD, and Osamu Iida, MD
ABSTRACT Purpose: To compare primary patency between MISAGO (Terumo Corporation, Tokyo, Japan) and S.M.A.R.T. CONTROL (Cordis Corporation, Miami Lakes, Florida), second-generation and first-generation nitinol stents, in femoropopliteal lesions. Materials and Methods: This multicenter, retrospective study included 240 cases with MISAGO stent implantation and 1,265 cases with S.M.A.R.T. stent implantation. The S.M.A.R.T. group had more Trans-Atlantic Inter-Society of Consensus (TASC) II class C/D lesions (53% vs 41%, P ¼ .001) and smaller reference vessel diameter (RVD) (5.3 mm ⫾ 0.9 vs 5.5 mm ⫾ 0.9, P o .001). Results: Kaplan-Meier estimates of 2-year primary patency after S.M.A.R.T. and MISAGO stent implantation were 67% and 55% (P ¼ .007). Interaction analysis revealed that TASC II classification and RVD had a significant influence on the association of MISAGO versus S.M.A.R.T. stents with the outcome. The study population was stratified according to TASC II classification and RVD, and MISAGO and S.M.A.R.T. stents were compared after propensity score matching. There was no significant difference in 2-year patency between the 2 stents in the subgroup with TASC II class A/B and RVD Z 5 mm (S.M.A.R.T. 82% ⫾ 4 vs MISAGO 74% ⫾ 5, P ¼ .480). MISAGO stents had lower primary patency than S.M.A.R.T. stents in cases with TASC II class C/D or RVD o 5 mm (S.M.A.R.T. 62% ⫾ 6 vs MISAGO 25% ⫾ 6, P ¼ .015). Conclusions: S.M.A.R.T. and MISAGO stents had similar patency in simple lesions, but MISAGO stents had lower patency than S.M.A.R.T. stents in more complex lesions.
ABBREVIATIONS CI = confidence interval, TASC = Trans-Atlantic Inter-Society of Consensus, TLR = target lesion revascularization
Femoropopliteal disease is the most common cause of symptomatic peripheral artery disease (1). Endovascular
therapy for femoropopliteal lesions is unsatisfactory in terms of postoperative vascular patency (2,3). Generally,
From the Department of Cardiology (K.S.), Saiseikai Central Hospital, Kyoto Prefectual University of Medicine, 1-4-17, Mita, Minato, Tokyo 108-0073, Japan; Department of Metabolic Medicine (M.T.), Osaka University Hospital, Osaka University, Osaka, Japan; Department of Cardiology (Y.Sh.), Shin-Koga Hospital, Kyushu University, Fukuoka, Japan; Cardiovascular Center (A.Ta.), Sendai Kousei Hospital, National Defense Medical College, Miyagi, Japan; Department of Cardiology (Y.So.), Kokura Memorial Hospital, Kochi University, Fukuoka, Japan; Department of Vascular Surgery (T.Y.), Matsuyama Red Cross Hospital, Kyushu University, Ehime, Japan; Department of Cardiology (A.To.), Kawakita General Hospital, Yamagachi University, Tokyo, Japan; Department of Cardiology (S.S.), Saka General Hospital, Gunma University, Miyagi, Japan; Department of Cardiology (K.D.), Morinomiya Hospital, Hyogo College of Medicine, Osaka, Japan; Department of Cardiology (T.T.), Kanazawa Medical University Hospital, Kanazawa Medical University,
Ishikawa, Japan; Department of Cardiology (A.K.), Saiseikai Nakatsu Hospital, Kobe University, Osaka, Japan; and Cardiovascular Division (O.I.), Kansai Rosai Hospital, Hyogo College of Medicine, Hyogo, Japan. Received November 15, 2015; final revision received and accepted May 29, 2016. Address correspondence to K.S.; E-mail: [email protected] M.T. receives personal fees from Johnson & Johnson K.K. Medical Company (Tokyo, Japan). None of the other authors have identified a conflict of interest. & SIR, 2016 J Vasc Interv Radiol 2016; XX:]]]–]]] http://dx.doi.org/10.1016/j.jvir.2016.05.042
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nitinol stents yield better patency rates than either plain balloon angioplasty or provisional stent deployment (4–7). Restenosis has been reported to occur in 21%– 31% of femoropopliteal vessels treated with a bare metal stent 1 year after implantation (8). New designs of nitinol stents have been introduced with the aim of improving long-term outcome (9–12). The MISAGO system (Terumo Corporation, Tokyo, Japan) is composed of a peripheral, nitinol, self-expanding stent and a rapidexchange delivery catheter. This system has been demonstrated to offer good conformability and resistance to fracture (10,11). The S.M.A.R.T. CONTROL stent (Cordis Corporation, Miami Lakes, Florida) is designed to deliver a self-expanding stent to femoropopliteal and iliac lesions (12). Although various other modalities have been applied to improve vessel patency, including drug-coated balloons (13–15), drug-eluting stents (16), and covered stents (17,18), atherectomy devices (19) and nitinol stents are widely available for femoropopliteal lesions. Moreover, comparative data on their efficacy are still few. The purpose of this study was to perform a retrospective comparison of multicenter data on the use of S.M.A.R.T. and MISAGO stents in the treatment of femoropopliteal lesions.
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Trial Registry, as recommended by the International Committee of Medical Journal Editors (no. UMIN000017658, REAL-SM registry: Retrospective multi-center comparison of S.M.A.R.T. and MISAGO stents in treatment of femoropopliteal lesions). Data from 10 cardiovascular centers on the use of MISAGO stents for femoropopliteal lesions between January 2013 and December 2013 were collected retrospectively. Among 277 patients who had the MISAGO stent deployed, 26 were excluded because of combined use with other stents, and 11 were excluded because of unavailable data. Consequently, 240 patients with MISAGO stent implantation were included in the analysis. Data on the S.M.A.R.T. stent were obtained from a retrospective analysis of a prospectively maintained multicenter database. Among 2,014 patients in whom a stent was successfully deployed for femoropopliteal lesions between January 2004 and December 2011, the S.M.A.R.T. stent was used in 1,495 patients. Among 1,495 patients in whom a S.M.A.R.T. stent was deployed, 230 were excluded because of unavailable data, leaving 1,265 patients to be included in the analysis. The baseline demographics are summarized in Table 1. All patients were required to attend the outpatient clinic of their hospital, and ankle-brachial index and duplex ultrasound were checked at 1, 3, 6, and 12 months and every 12 months thereafter for follow-up evaluation.
MATERIALS AND METHODS Study Design
Definitions
The study was approved by the ethics committee of each participating institution and registered with the University Hospital Medical Information Network-Clinical
Restenosis was defined as peak systolic velocity ratio 4 2.4 on duplex ultrasound, 4 50% stenosis on angiography or computed tomography, or a decrease
Table 1 . Baseline Characteristics of Overall Study Population
n Age, y Male sex Smoking Hypertension Dyslipidemia Diabetes mellitus
S.M.A.R.T.
MISAGO
1,265
240
P Value
73 ⫾ 9
72 ⫾ 9
.584
891 (70%) 800 (63%)
156 (65%) 151 (63%)
.108 .942
1,112 (88%)
194 (81%)
.005
910 (72%) 824 (65%)
187 (78%) 148 (62%)
.058 .304
Regular dialysis
301 (24%)
72 (30%)
.050
Chronic heart failure Critical limb ischemia
139 (11%) 402 (32%)
42 (18%) 83 (35%)
.007 .408
ABI before revascularization
0.60 ⫾ 0.22
0.60 ⫾ 0.21
.854
Aortoiliac lesion Poor below-the-knee runoff
225 (18%) 579 (46%)
44 (18%) 119 (50%)
.854 .290
TASC II class C/D
674 (53%)
99 (41%)
.001
Lesion length, cm Chronic total occlusion
14 ⫾ 9 699 (55%)
12 ⫾ 8 89 (37%)
o.001 o.001
Reference vessel diameter, mm
5.3 ⫾ 0.9
5.5 ⫾ 0.9
o.001
Note–Data are presented as mean ⫾ SD or number (%). Intergroup difference was tested by unpaired t-test for continuous variables and by Fisher exact test for dichotomous variables. ABI ¼ ankle-brachial index; TASC ¼ Trans-Atlantic Inter-Society of Consensus.
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of 0.2 in resting ankle-brachial index. The complete absence of a detectable signal was graded as complete occlusion. Radiographs were obtained for evaluation of stent fractures. Primary patency was defined as no restenosis or repeat revascularization in the treated vessel, and secondary patency was defined as reopening or redilation of a totally occluded or stenosed vessel by repeat revascularization. Calcification was assessed by fluoroscopic visualization of calcium deposits. A diagnosis of diabetes was based on the World Health Organization criteria (20). Hypertension was defined as systolic blood pressure Z 140 mm Hg or diastolic pressure Z 90 mm Hg. Dyslipidemia was defined as serum low-density lipoprotein cholesterol level Z 140 mg/dL, high-density lipoprotein cholesterol level r 40 mg/dL, or triglycerides Z 150 mg/dL. Poor cardiac function was defined as an ejection fraction of o 40%.
Statistical Analysis The data are presented as mean ⫾ SD for continuous variables and number (percentage) for discrete variables, if not otherwise described. A P value of o .05 was considered to be statistically significant. Primary patency, defined as freedom from restenosis after stent implantation, was determined by the Kaplan-Meier method, and intergroup differences were assessed by the log-rank test. The Cox proportional hazard regression model was used to investigate the association between the use of each type of stent and future risk of restenosis. The hazard ratio and 95% confidence interval (CI) were determined. Stratification analysis of the following background characteristics was also performed: sex, age, smoker, hypertension, dyslipidemia, diabetes mellitus, regular dialysis, chronic heart failure, critical limb ischemia, coexistence of aortoiliac lesion, poor runoff (defined as no or only 1 intact below-theknee vessel), Trans-Atlantic Inter-Society of Consensus (TASC) II classification, and reference vessel diameter. The P values for interactions between these variables and MISAGO versus S.M.A.R.T. stent implantation are also reported. Variables showing a significant interactive effect on restenosis with the use of each type of stent were used to stratify the study population to obtain a comparison of primary patency in each subgroup. To minimize intergroup differences in baseline characteristics, the comparison was performed after propensity score matching. The propensity score was obtained by using a logistic regression model in which confounders were included as explanatory variables. We selected the confounder variables that were expected to influence clinical decisions on stent selection and were available in our databases. The variables selected were sex, age, smoking, hypertension, dyslipidemia, diabetes mellitus, regular dialysis, chronic heart failure, critical limb ischemia, coexistence of an aortoiliac lesion, poor runoff, TASC II
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classification, reference vessel diameter, and stent diameter. We included all these variables in the matching, regardless of statistical significance of the association. One-to-one pair matching was performed using the nearest neighbor method without replacement. According to Austin’s recommendation (21), we matched to the logit of the propensity score ⫾ 0.2 SD. The development of the propensity score and the subsequent matching based on the score was performed separately in each subgroup. A paired analysis of intergroup differences was performed after matching. R version 3.1.0 (R Development Core Team, R Foundation for Statistical Computing, Vienna, Austria) was used for propensity score matching. All other analyses were performed with IBM SPSS Statistics for Windows version 22 (IBM Corporation, Armonk, New York).
RESULTS In the S.M.A.R.T. group, the mean follow-up period was 647 days ⫾ 513 (1.8 y ⫾ 1.4), and restenosis was observed in 387 cases. In the MISAGO group, the mean follow-up period was 369 days ⫾ 291 (1.0 y ⫾ 0.8), and restenosis was observed in 69 cases. The 1-year and 2year follow-up rates were 81% (1,019 of 1,265) and 62% (782 of 1,265) in the S.M.A.R.T. group and 68% (162 of 240) and 35% (85 of 240) in the MISAGO group. In the S.M.A.R.T. group, 228 cases (18%) of the 1,019 noncensored cases had restenosis at 1 year, and 332 cases (26%) of the 782 noncensored cases had restenosis at 2 years. In the MISAGO group, 29 cases (36%) of the 162 noncensored cases had restenosis at 1 year, and 68 cases (80%) of the 85 noncensored cases had restenosis at 2 years. A crude analysis revealed a significant intergroup difference in primary patency (P ¼ .007) (Fig 1). The stratification analyses were then performed (Fig 2). TASC II class C/D and reference vessel diameter o 5 mm showed a significant interaction effect on the association of MISAGO stent versus S.M. A.R.T. stent with restenosis. This finding suggested that the MISAGO stent was inferior to the S.M.A.R.T. stent in terms of primary patency in patients with TASC II class C/D or reference vessel diameter o 5 mm but comparable in other patients. Therefore, the study population was stratified into 1 of the following 2 subgroups for further analysis: (a) patients with TASC II class C/D or reference vessel diameter of o 5 mm or (b) patients with TASC II class A/B or reference vessel diameter of Z 5 mm. After stratification, propensity score matching was performed in each subgroup. Matching yielded 129 pairs in the subgroup with TASC II class A/B or reference vessel diameter Z 5 mm and 109 pairs in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (Fig 3a, b). No significant intergroup difference was observed in baseline characteristics after matching in the
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Figure 1. Primary patency after S.M.A.R.T. and MISAGO stent implantation in the overall unmatched population.
Figure 2. Association of MISAGO versus S.M.A.R.T. stent implantation with restenosis risk. Data are unadjusted hazard ratios for restenosis and their 95% CIs, obtained from the Cox proportional hazard regression analysis. P values are for individual interaction effects of MISAGO versus S.M.A.R.T. stent implantation and background characteristics.
2 subgroups (Table 2). There was also no significant difference in lesion length in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm (7 cm ⫾ 3 in the S.M.A.R.T. group and 7 cm ⫾ 4 in the MISAGO group, P ¼ .731) or the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (18 cm ⫾ 6 in the S.M.A.R.T. group and 17 cm ⫾ 8 in the MISAGO group, P ¼ .895). The ratio of reference vessel diameter to stent diameter (vessel-to-stent diameter ratio) also showed no significant difference in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm (0.87 ⫾ 0.11 in the S.M.A.R.T. group and 0.88 ⫾ 0.12 in the MISAGO group, P ¼ .736) or the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (0.84 ⫾ 0.12 in the S.M.A.R.T. group and 0.82 ⫾ 0.14 in the MISAGO group, P ¼ .468). Subsequently, primary patency was investigated in the matched population in each subgroup. In the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm, the S.M.A.R.T. group had a mean follow-up of 709 days ⫾ 543, with restenosis observed in 26 cases, whereas the MISAGO group had a mean follow-up of 445 days ⫾ 343, with restenosis observed in 24 cases. In contrast, in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm, the S.M.A.R.T. group had a mean follow-up of 599 days ⫾ 467, with restenosis observed in 35 cases, whereas the MISAGO group had a mean follow-up of 280 days ⫾ 182, with restenosis observed in 45 cases. As shown in Figure 4a, no significant difference was observed between MISAGO and S.M.A.R.T. stent implantation in the subgroup with TASC II class A/B and reference vessel
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Figure 3. Distribution of propensity scores in matched and unmatched populations with MISAGO versus S.M.A.R.T. stent implantation. (a) Distribution of propensity scores in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm. (b) Distribution of propensity scores in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm. The distribution of the score across the matched MISAGO and S.M.A.R.T. groups was quite similar, indicating that clinical probability (or propensity) to select the MISAGO versus S.M.A.R.T. stent was well matched between the 2 groups.
Table 2 . Baseline Characteristics of Matched Study Population TASC II Class A/B and Reference
TASC II class C/D or Reference
Diameter Z 5 mm
Diameter o 5 mm
S.M.A.R.T. (n ¼ 129) MISAGO (n ¼ 129) P Value S.M.A.R.T. (n ¼ 109) MISAGO (n ¼ 109) P Value Age, y Male sex
72 ⫾ 9 92 (71%)
72 ⫾ 9 94 (73%)
.555 .897
74 ⫾ 10 66 (61%)
73 ⫾ 9 62 (57%)
.105 .694
Smoking
79 (61%)
82 (64%)
.798
66 (61%)
68 (62%)
.897
Hypertension Dyslipidemia
104 (81%) 97 (75%)
104 (81%) 97 (75%)
1.000 1.000
93 (85%) 87 (80%)
89 (82%) 88 (81%)
.584 1.000
Diabetes mellitus
79 (61%)
75 (58%)
.699
71 (65%)
72 (66%)
1.000
Regular dialysis Chronic heart failure
35 (27%) 16 (12%)
36 (28%) 17 (13%)
1.000 1.000
41 (38%) 28 (26%)
35 (32%) 22 (21%)
.480 .532
Critical limb ischemia
43 (33%)
43 (33%)
1.000
41 (38%)
39 (36%)
.883
Aortoiliac lesion Poor below-the-knee runoff
24 (19%) 56 (43%)
25 (19%) 56 (43%)
1.000 1.000
14 (13%) 57 (52%)
17 (16%) 61 (56%)
.664 .643
TASC II class C/D
0 (0%)
0 (0%)
—
95 (87%)
97 (89%)
.832
Reference diameter o 5 mm
0 (0%)
0 (0%)
—
27 (25%)
32 (29%)
.511
Note–Data are presented as mean ⫾ SD or number (%). Intergroup difference was tested by paired t-test for continuous variables and by McNemar test for dichotomous variables. TASC ¼ Trans-Atlantic Inter-Society of Consensus.
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Figure 4. Primary patency after S.M.A.R.T. and MISAGO stent implantation in the matched population. (a) Primary patency in cases with TASC II class A/B and reference vessel diameter Z 5 mm. (b) Primary patency in cases with TASC II class C/D or reference vessel diameter o 5 mm.
diameter Z 5 mm (P ¼ .480). In contrast, MISAGO stent implantation yielded a significantly lower rate of primary patency than S.M.A.R.T. stent implantation in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (P ¼ .015) (Fig 4b). Similarly, the MISAGO group had a significantly higher risk for target lesion revascularization (TLR) compared with the S.M. A.R.T. group in the subgroup with TASC II class C/D or reference vessel diameter o 5 mm (P ¼ .022) but not in the subgroup with TASC II class A/B and reference vessel diameter Z 5 mm (P ¼ .273) (Fig 5a, b).
Stent Fracture In the overall population before matching, 76 cases of stent fracture were observed in the S.M.A.R.T. group, accounting for 5% of patients with S.M.A.R.T. stents. No stent fractures were observed in the MISAGO group. In the S.M.A.R.T. group, stent fracture was significantly associated with restenosis and TLR; the hazard ratios were calculated to be 1.88 (95% CI, 1.36–2.60, P o .001) for restenosis and 1.92 (95% CI, 1.36–2.68, P o .001) for TLR, respectively.
DISCUSSION In this retrospective multicenter study, 2-year patency was investigated in 2 types of nitinol stents. The results
revealed that the S.M.A.R.T. stent provided superior primary patency. Moreover, our stratification analysis showed that a TASC II class C/D lesion or reference vessel diameter of o 5 mm was more strongly associated with risk of stenosis with the MISAGO stent than with the S.M.A.R.T. stent. Numerous novel modalities have been used to treat femoropopliteal lesions. Studies on the use of drugcoated balloons in femoropopliteal interventions have shown that the rate of 6-month TLR were 4%–7% (13,15) in various subsets of femoropopliteal lesions. Covered stents (17) have also been used in cases of long diffuse femoropopliteal lesions, and a 1-year patency indicated 78.1%. A 1-year primary patency of 78% was demonstrated with use of atherectomy devices to treat infrainguinal lesions of up to 20 cm in length (18). Vessel recoil, dissection, and suboptimal results often occur in balloon angioplasty, and they are related to poor outcome (4). Graft thrombosis is another problem encountered with the use of covered stents (17). For these reasons, nitinol stents still play an important role in femoropopliteal interventions. Although the primary patency of nitinol stents showed no advantage over angioplasty in the treatment of short femoropopliteal lesions (22), their efficacy has been apparent in long lesions. The ABSOLUTE and RESILIENT trials repor-
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Figure 5. Freedom from TLR after S.M.A.R.T. and MISAGO stent implantation in the matched population. (a) Rate of freedom from TLR in cases with TASC II class A/B and reference vessel diameter Z 5 mm. (b) Rate of freedom from TLR in cases with TASC II class C/D or reference vessel diameter o 5 mm.
ted that nitinol stents yield superior patency to balloon angioplasty (4,5). Mean lesion length in the present study, which included severe diffuse lesions, was 15 cm. The MISAGO stent demonstrated good conformability and excellent resistance to stent fracture; thus, a special feature of the MISAGO stent is flexibility. Although a relatively high rate of stent fracture was reported with the S.M.A.R.T. stent (23), it does offer stronger radial force (24). In the present study, a primary patency of 86% at 1 year and 75% at 2 years was observed with the MISAGO stent in the TASC A/B and reference vessel diameter Z 5 mm subgroup. This result was consistent with results of the MISAGO 2 study (11). Taken together, it is suggested that the MISAGO stent offers relatively good patency in simple lesions. In the same way, the present results for the S.M.A.R.T. stent in the TASC A/B and reference vessel diameter Z 5 mm subgroup were similar to the results of the STROLL study (12). In simple lesions, 2-year primary patency showed no difference between the 2 types of stent. However, the present results differed between each type of stent in the TASC II class C/D or reference vessel diameter o 5 mm subgroup in that primary patency with the MISAGO was lower than that with the S.M.A.R.T. stent. These data suggest that the maintenance of vessel patency requires stronger radial force in diffuse, long
lesions. In general, femoropopliteal stents are exposed to bending, compression, and twisting secondary to repetitive flexion of the joint. More flexible stents were introduced because stent fracture was associated with poor patency (23). However, although flexibility is important, radial force may be even more important. It was reported that the minimal stent area was related to less primary patency (25). Subintimal angioplasty was performed in many femoropopliteal cases. Stent underexpansion was often observed in subintimal angioplasty. A flexible stent such as the MISAGO may need to perform at high pressure after dilation. Woven nitinol stents were shown to exhibit greater radial force and produce favorable results in popliteal lesions (26). Taken together, these results suggest that both strong radial force and high resistance to stent fracture are necessary requirements in femoropopliteal stents. This study had several limitations, which may have skewed the clinical outcomes. First, although a propensity matched analysis was performed, this was a retrospective and nonrandomized study with a large sample size. Second, the observation period in the MISAGO group was shorter than the observation period in the S. M.A.R.T. group because the MISAGO stent was clinically approved later than the S.M.A.R.T. stent. Third, the sample size was too small to investigate the cutoff point of reference vessel diameter in more detail. Fourth,
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MISAGO vs S.M.A.R.T. Stent in Femoropopliteal Lesions
the data on stent fracture were obtained only at the final follow-up evaluation. Fifth, this study had no data about overlap after balloon dilation or stent placement. Lastly, the observation period was longer for the S.M.A.R.T. group than for the MISAGO group, and the apparently high stent fracture rate in the S.M.A.R.T. group might be due to this longer observation duration. Therefore, the study was inconclusive regarding interstent comparison of stent fracture rates. In conclusion, the S.M.A.R.T. stent showed superior efficacy to the MISAGO stent in terms of 2-year patency. The difference between the 2 types of stent was more obvious in cases with TASC II class C/D or a reference vessel diameter o 5 mm.
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