Extent and distribution of in-stent intimal hyperplasia and edge effect in a non-radiation stent population

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Abstract

Intimal hyperplasia within the body of the stent is the primary mechanism for in-stent restenosis; however, stent edge restenosis has been described after brachytherapy. Our current understanding about the magnitude of in vivo intimal hyperplasia and edge restenosis is limited to data obtained primarily from select, symptomatic patients requiring repeat angiography. The purpose of this study was to determine the extent and distribution of intimal hyperplasia both within the stent and along the stent edge in relatively nonselect, asymptomatic patients scheduled for 6-month intravascular ultrasound (IVUS) as part of a multicenter trial: Heparin Infusion Prior to Stenting. Planar IVUS measurements 1 mm apart were obtained throughout the stent and over a length of 10 mm proximal and distal to the stent at index and follow-up. Of the 179 patients enrolled, 140 returned for repeat angiography and IVUS at 6.4 ± 1.9 months and had IVUS images adequate for analysis. Patients had 1.2 ± 0.6 Palmaz-Schatz stents per vessel. There was a wide individual variation of intimal hyperplasia distribution within the stent and no mean predilection for any location. At 6 months, intimal hyperplasia occupied 29.3 ± 16.2% of the stent volume on average. Lumen loss within 2 mm of the stent edge was due primarily to intimal proliferation. Beyond 2 mm, negative remodeling contributed more to lumen loss. Gender, age, vessel location, index plaque burden, hypercholesterolemia, diabetes, and tobacco did not predict luminal narrowing at the stent edges, but diabetes, unstable angina at presentation, and lesion length were predictive of in-stent intimal hyperplasia. In a non-radiation stent population, 29% of the stent volume is filled with intimal hyperplasia at 6 months. Lumen loss at the stent edge is due primarily to intimal proliferation.

Section snippets

Study design and patient population

The HIPS trial was a randomized, prospective, multicenter study comparing the safety and efficacy of locally delivered versus intraluminal heparin in patients who underwent IVUS-guided Palmaz-Schatz stenting.6 In all, 179 patients were randomized at 11 centers in North America and Europe; each patient had 1 focal, de novo stenosis in a native coronary artery. The protocol was designed to reflect the current practice of stent implantation in stable patients. Therefore, patients were typical of

Results

Subjects returned for 6-month angiography and IVUS as per protocol rather than based on clinical presentation. At the time of follow-up IVUS, 90% had only class I or class II angina and 95% had negative stress tests. There was no difference in any IVUS parameter between the 2 forms of heparin delivery: local versus systemic heparin.6

Discussion

In this group of asymptomatic or minimally symptomatic nonradiation patients, IH volume 6 months after stenting of focal, de novo coronary lesions ranged from none to 123 mm3, corresponding to 0% to 86% of the stent volume. The mean IH volume was 29% of the stent volume, but there was a very high variability in volume and distribution. In addition, the neointima appeared to extend 2 mm beyond the stent causing edge lumen loss.

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This study was supported by a grant from LocalMed, Inc., Palo Alto, California. Manuscript received and accepted February 19, 2001.

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