Comparison of Vessel Response following Sirolimus-Eluting Stent Implantation as Assessed by Serial 3-D Intravascular Ultrasound

Materials and Methods

Our IVUS database was queried to identify patients who met the following criteria: (1) successful treatment with SES; (2) complete serial (post-PCI and 6- to 8-month follow up) IVUS studies; and (3) high-quality automated pullback IVUS images within stented segments and up to 5 mm at adjacent segments outside each stent edge. A total of 94 patients met the enrollment criteria. Patients were divided into two groups according to treatment vessel: LAD (n = 41) and non-LAD (LCX n = 32; RCA n = 21). The institutional review board approved the protocol, and written informed consent was obtained from each patient.
IVUS analysis. All IVUS studies were performed according to the standard procedure at post-PCI and 6- to 8-month follow up using a commercially available IVUS system (30 MHz or 40 MHz IVUS catheter, Boston Scientific Corp., Natick, Massachusetts). Volumetric analysis was performed using a PC-based software (Echoplaque™, Indec Systems, Inc., Mountain View, California) as previously described.⁶ Volume index was calculated as vessel volume divided by the length. Cross-sectional narrowing (CSN) was defined as neointimal area divided by stent area (%).
Statistical analysis. Statistical analysis was performed using Statview 5.0 (SAS Institute, Cary, North Carolina). Categorical variables are presented as numbers (percentages) and compared using the Chi-square test. Continuous variables are presented as mean ± standard deviation (SD). Continuous variables between post-PCI and follow up are compared using the Student’s paired t-test; otherwise, the unpaired t-test was used. A value of p <0.05 was considered statistically significant.

Results

Baseline characteristics and IVUS measurements within the stented segment at post-PCI were not significantly different between the LAD and non-LAD lesions (Table 1). At follow up, maximum CSN was significantly greater in the non-LAD lesions (Table 2). With respect to reference segments, post-PCI IVUS measurements were not significantly different between the LAD and non-LAD lesions, however, follow-up LVI at the proximal reference was significantly smaller in the non-LAD lesions. In the non-LAD lesions, VVI and LVI at the proximal reference showed significant changes between post-PCI and follow up (Table 3). Delta LVI (follow-up LVI minus post-PCI LVI) was significantly greater in the non-LAD lesions (Figure 1). At the distal reference segment, there was no significant difference between the LAD and non-LAD lesions.

Discussion

This detailed IVUS analysis showed a greater luminal loss in the non-LAD lesions in the in-stent segment and proximal reference segment following SES implantation as compared with the LAD lesions. CSN was significantly greater in the non-LAD lesions, showing a greater amount of neointimal hyperplasia. Larger luminal loss in the proximal reference segment in the non-LAD group was primarily due to negative remodeling.
Classically, LAD lesions have been associated with higher rates of restenosis and subsequent adverse coronary events with balloon angioplasty and first-generation intracoronary stents.^1–3 With the use of current bare-metal stents and debulking devices, these differences became less distinct, and there was even a trend toward better outcomes in LAD lesions.⁷ The recent advent of drug-eluting stents (DES) considerably reduced restenosis, decreasing subsequent adverse clinical events. Of particular interest, a recent study has shown non-LAD lesions as one of the predictors of in-stent restenosis following SES implantation,⁴ and another study suggests a trend toward a lower rate of target lesion revascularizations in LAD lesions.⁵ The clinical results of SES are concordant with the present IVUS study showing less luminal loss in LAD lesions.
Stent implantation causes conformational changes in vessel geometry,⁸ and implantation of rigid stents within the coronary arteries may result in flexion or hinge points at the ends of stents.⁹ These points have been associated with increased rates of restenosis in bare-metal stents.¹⁰ The determinants of neointimal hyperplasia with DES have not been clearly established. However, local mechanical conditions including step-up, step-down,¹¹ and shear stress¹² are thought to contribute to neointimal hyperplasia. Different vessel behavior between LAD and non-LAD lesions possibly results from the different local conditions between these vessels.
Current SES utilize a rigid bare-metal platform, which is potentially vulnerable to mechanical distortion over time. Stent fractures, presumably a result of chronic mechanical damage, are typically seen in the right coronary artery, possibly resulting from larger stress by cardiac cycles within long stents.¹³ Mechanical and pharmacological properties of DES may have specific requirements for different vessel locations. Understanding vessel behavior following stent implantation may help in the development of future DES tailored for particular vessel morphology, location, and curvature.

Study limitations. There are several limitations in this study. First, this study is based on a relatively limited sample size with serial IVUS studies, raising the possibility of selection bias. Second, there are several inherent limitations in three-dimensional analysis techniques, including the effects of motion artifact and distortion due to curvature of the vessels.¹⁴ Third, this analysis included only SES, hence these results may not be applicable to other DES.

Conclusions

This detailed IVUS analysis suggests that there are minimal differences in vessel responses following SES implantation. These findings may have potential implication for mechanical and pharmacokinetic properties of next-generation DES technology.

References

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