Intravascular Ultrasound Comparison of Small Coronary Lesions Between Novel Guidewire-Based Sirolimus-Eluting Stents and Conventional Sirolimus-Eluting Stents

Author(s): 

Teruyoshi Kume, MD, PhD1, Katsuhisa Waseda, MD, PhD1, Bon-Kwon Koo, MD, PhD1, Roberto Botelho, MD2, Stefan Verheye, MD, PhD3, Robert Whitbourn, MD4, Ian Meredith, MD, PhD5, Stephen Worthley, MD, PhD6, Koh Tian Hai, MD7, Paul G. Yock, MD1, Flavio Roberto Azevedo de Oliveira, MD, PhD8, Alexandre Abizaid, MD, PhD8, Peter J. Fitzgerald, MD, PhD1, Yasuhiro Honda, MD1

Abstract: Background. The Sparrow stent system (Biosensors International) consists of a self-expanding, ultra-thin nitinol stent mounted within a 0.014˝ guidewire designed for small or tortuous coronary lesions. We compared the intravascular ultrasound (IVUS) findings between the novel self-expanding sirolimus-eluting stent (Sparrow-SES) and a conventional balloon-expandable sirolimus-eluting stent (Cypher-SES) in patients with small coronary disease. Methods. We examined 14 lesions treated with the Sparrow-SES from CARE II, compared with 22 small vessel lesions treated with Cypher-SES. IVUS examination was performed post-procedure and 8 months later. Volumetric data were standardized by length as volume index (VI; mm3/mm). Results. While baseline stent VI trended smaller in Sparrow-SES, follow-up stent VI became similar between the 2 groups due to a significant increase of stent VI in self-expanding Sparrow-SES during the follow-up period. At 8 months, Sparrow-SES showed greater neointima than Cypher-SES (0.8 ± 0.6 mm3/mm vs 0.2 ± 0.2 mm3/mm; P<.001). However, the decrease in lumen VI was only 0.3 ± 0.7 mm3/mm in Sparrow-SES, as compared to 0.1 ± 0.3 mm3/mm in Cypher-SES (P=.259), since the late loss due to neointimal hyperplasia was partly counterbalanced by the chronic stent expansion in Sparrow-SES. Conclusion. While 8-month follow-up of Sparrow-SES revealed greater amounts of neointimal hyperplasia compared with conventional Cypher-SES, chronic stent expansion preserved the lumen by increasing stent volume. This novel, guidewire-based, self-expanding stent system designed to be delivered through complex anatomies may be useful to treat patients with small-caliber coronary lesions by offering sufficient lumen preservation at follow-up. 

J INVASIVE CARDIOL 2012;24(10):489-493

Key words: coronary, small-vessel disease, percutaneous coronary intervention, drug-eluting stent

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Percutaneous coronary intervention (PCI) targeting small coronary arteries comprises up to 35% of all catheter-based procedures in daily practice.1 In the bare-metal stent (BMS)era, smaller vessel diameter was a recognized determinant of restenosis after PCI.2,3 The drug-eluting stent (DES) has significantly reduced stent restenosis rates, yet PCI in small coronary arteries remains a challenging lesion subset in the DES era.4 In addition, failure to cross the tight lesion (with the undeployed stent) due to vessel tortuosity represents another challenge of PCI in the treatment of small coronary artery disease, having design implications for small-vessel stent delivery systems with drug elution and crossing profile.

Previously, a feasibility study of a guidewire-based, self-expanding stent delivery system, the Sparrow stent system (CardioMind; purchased by Biosensors International), was reported.5,6 These encouraging preliminary clinical results of the use of the Sparrow stent have led to the development of a drug-eluting version for this platform.7,8 Coupled with guidewire-based crossing profile and sirolimus, a well-established anti-proliferative drug,9 this DES iteration of the Sparrow stent may be more useful to treat small vessel coronary disease than conventional catheter based DES platforms. Thus, this study was performed as an initial investigation to compare the intravascular ultrasound (IVUS) findings between the novel Sparrow sirolimus-eluting stent (Sparrow-SES, Biosensors International) with those of conventional balloon-expandable sirolimus-eluting stents (Cypher-SES, Cordis) in patients with small vessel coronary artery disease. 

Methods

Patient selection. The study population for the analysis of the Sparrow-SES consisted of patients with IVUS analysis from the CARE II trial implanted with the Sparrow-SES. The CARE II trial was a 3 arm prospective, randomized, multicenter single-blind trial evaluating the safety and efficacy of the Sparrow-SES compared to the Sparrow bare-metal stent and a commercial bare-metal stent in the treatment of single de novo small native coronary artery lesions.7,8 Conventional balloon-expandable Cypher-SES data were derived from the SVELTE trial, a prospective, multicenter trial of Cypher-SES in the treatment of single de novo small coronary disease, and the ENDEAVOR III trial (Cypher-SES arm), a multicenter, single-blind, parallel, 2-arm, randomized control study comparing the efficacy of zotarolimus-eluting stents and Cypher-SES for the treatment of de novo coronary artery lesions.10,11 From these trials, patients who met the following criteria were enrolled into this IVUS analysis: (1) a single de novo >50% stenosis, in a native epicardial coronary vessel between 2.0 and 2.5 mm in diameter; and (2) availability of high-quality, serial (baseline and follow-up) IVUS images with volumetric analysis.

Device description. The Sparrow-SES delivery system is comprised of the self-expanding nitinol stent, which is loaded into a 0.014˝″guidewire platform. This self-expanding stent was able to be delivered to the target lesion after balloon angioplasty and released from the wire under the guidance of two radiopaque markers at both edges of the stent by electrolysis. In the CARE II trial, the stent deployment was followed by mandated postdilation per protocol to ensure optimal stent expansion and complete stent apposition to the vessel wall. A detailed description of the stent deployment procedure was provided in a previous case report.5 This stent employs a closed-cell design with metal-to-artery ratio of 8%-12% and incorporates sirolimus in a biodegradable PLA/PGLA block copolymer matrix. Comparisons of the Sparrow-SES and Cypher-SES device characteristics are shown in Table 1 and representative IVUS images of both stent are shown in Figure 1.

IVUS analysis. IVUS examination was performed at post-procedure and 8 months later. The IVUS procedure was performed in a standard fashion using automated motorized pullback (0.5 mm/s) with commercially available imaging systems (40 MHz IVUS catheter, Boston Scientific Corporation, or 20 MHz IVUS catheter, Volcano Corporation). IVUS analysis was performed at an independent core laboratory by clinicians blinded to the treatment arm. Volumetric measurements were performed using a PC based software (echoPlaque; Indec Systems Inc) as previously described.12,13 Peristent plaque volume was calculated as vessel minus stent volume. Neointimal volume was calculated as stent minus lumen volume, and neointimal obstruction (%) was defined as neointimal volume divided by stent volume. Each volume was divided by the measurement of stent length to adjust for different stent lengths (volume index: VI, mm3/mm). Cross-sectional narrowing (%) was defined as neointima area divided by stent area.

Tissue prolapse, stent edge dissection, and incomplete stent apposition (ISA) were assessed by qualitative IVUS analysis. ISA was defined as 1 or more struts clearly separated from the vessel wall with evidence of blood speckles behind the strut. ISA was classified as ‘persistent,’ ‘resolved,’ or ‘late-acquired’ as previously described.13,14 All images were reviewed by two independent observers and adjudication of opinion was based on the consensus of these observers.

Statistical analysis. Statistical analysis was performed with SPSS version 18.0 for Windows (SPSS Inc). Categorical variables were presented as counts and percentages, and compared with the Fisher exact test or the chi-square test. Continuous variables were presented as mean value ± standard deviation (SD) after testing the normality of the data with the Kolmogorov-Smirnov test or Saphiro-Wilks test. For continuous variables, Student’s t-test was used to differentiate between two sets of data (paired and unpaired according to the compared data). A P-value of <.05 indicated statistical significance.

Results

Serial IVUS images were analyzed in 14 small coronary lesions treated with the Sparrow-SES and 22 with the Cypher-SES. There were no significant differences in baseline demographic, clinical, and procedural characteristics between the Sparrow-SES and Cypher-SES (Table 2), and thus, no propensity score matching was performed. While baseline stent VI trended smaller in the Sparrow-SES, follow-up stent VI became similar between the 2 groups due to a significant increase in stent VI of the self-expanding Sparrow-SES during the follow-up period (Table 3). Individual changes of stent VI are shown in Figure 2 with change in the Sparrow-SES significantly greater than in the Cypher-SES (14.6% vs 1.8%). At 8-month follow-up, the Sparrow-SES showed greater neointima VI and percent neointimal obstruction than those of the Cypher-SES group (Table 3). However, the decrease in lumen VI was only 0.3 ± 0.7 mm3/mm in the Sparrow-SES group, as compared to 0.1 ± 0.3 mm3/mm in the Cypher-SES (P=.259), since the late loss due to neointimal hyperplasia was partly counterbalanced by the chronic stent expansion in the Sparrow-SES (Figure 3). Table 4 presents the quantitative IVUS results for the reference segments, showing that vessel, plaque, and lumen VI did not change significantly in either group. Regarding the results of qualitative analyses, no significant differences between the Sparrow-SES and Cypher-SES in either tissue prolapse or stent edge dissection were observed (Table 5). However, there was a trend toward more ISA at baseline in the Sparrow-SES than in the Cypher-SES (8 cases in the Sparrow-SES, 5 cases in the Cypher-SES; P=.073). Resolved ISA was observed in 7 of 8 cases (87.5%) in the Sparrow-SES group and 2 of 5 cases (40.0%) in the Cypher-SES group.


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