Long-Term Imaging Study Evaluates Vascular Healing in First-Gen DES

PARIS, France—While long-term neointimal thickness and volume are low and similar between paclitaxel- (PES) and sirolimus-eluting stents (SES), the persistence of uncovered struts and differences in protruding/malapposed struts indicate that incomplete vascular healing clusters in a few, select lesions, according to 5-year imaging data released May 19 at EuroPCR 2011.

For the SIRTAX LATE study, researchers led by Stephan Windecker, MD, of Bern University Hospital (Bern, Switzerland), used optical coherence tomography (OCT) to assess markers of arterial healing 5 years after SES (n = 41 patients / 41 lesions) and PES (n = 47 patients / 47 lesions) implantation. The investigators undertook the research as a complement to the autopsy studies that identified uncovered stent struts and strut malapposition as risk factors for stent thrombosis in first-generation DES.

With a reference vessel diameter of 2.89 ± 0.50 mm for SES and an almost identical 2.89 ± 0.44 mm for PES, angiographic results showed similar in-stent measurements for minimum lumen diameter (MLD), percent diameter stenosis, and late loss (table 1).

Table 1. Five-Year Angiographic Results

On OCT analysis, neointimal thickness was an identical 0.11 mm in both groups, while neointimal area was also low and equivalent (0.97 mm² with SES and 1.03 mm² with PES; P = 0.46).

Uncovered struts were infrequent, with 1.0% of 6,380 SES struts and 1.5% of 6,782 PES struts remaining uncovered. The rate of lesions with more than 5% uncovered struts was also similar at 10.7% with SES and 7.2% with PES (P = 0.60).

The overall rate of stent strut malapposition at 5 years was also low in the SES (1.2%) and PES (0.7%) groups (P = 0.23). But patients receiving SES had significantly more lesions with greater than 5% malapposed struts than those receiving PES (24.0% vs. 5.7%; P = 0.03). The same was true for lesions with greater than 5% stent strut protrusion (3.7% with SES vs. 0.3% with PES; P = 0.07), though the difference did not reach statistical significance. In addition, outward bulges in the arterial wall, or saccular evaginations, per 100 frames were likewise higher with SES (17.0 vs. 7.0; P = 0.003).

The researchers also took cross sections every 1 mm across the entire stent length to construct geographical maps for each group. These maps showed a clustering of uncovered and malapposed struts in only a handful of lesions.

Dr. Windecker concluded that while neointimal thickness and volume are low and of similar magnitude for SES and PES at 5 years, long-term follow-up shows a higher rate of malapposed and protruding struts with SES compared with PES, while strut coverage is similar between the 2 DES.

In addition, “the persistence of uncovered struts, and the difference in protruding/malapposed struts and saccular evaginations suggest that vascular healing remains incomplete 5 years after implantation of early-generation DES,” he said. “Lesion-level analysis and geographical maps nicely demonstrate clustering of uncovered, malapposed or protruding struts in only a few lesions, whereas most lesions show nearly complete healing.”

Best of the Best?

In response to a question from panelist Mitchell W. Krucoff, MD, of the Duke Clinical Research Institute (Durham, NC), Dr. Windecker noted that clinically, the patients did well out to 5 years, with no adverse events.

This prompted Dr. Krucoff to comment that “I almost feel like this is the reverse of talking to Renu Virmani, who sees only the worst of the worst. Are these the best of the best? Are these the patients who 5 years out, all those who have already had stent thrombosis or repeat revascularization are eliminated and this is as good as it gets?”

“I think the observations of the autopsy studies were instrumental in our understanding of adverse events, but we were frightened about the extent and frequency of these observations, and therefore this investigation is complementary in the sense that it looks at event-free patients at long-term follow-up,” Dr. Windecker responded, noting that the study’s primary contribution is that “in the vast majority, there is good information in terms of strut coverage and overall vessel healing, and negative appearances, the meaning of which we do not completely understand, are limited to a few lesions.”

Therefore, it is very important that OCT studies should analyze not just struts but also individual lesions, he advised.

Study Details

Baseline characteristics were similar for the PES and SES groups, with about one-third of patients presenting with STEMI and an overall LVEF of 58%. In terms of lesion characteristics, patients received an average of 1.16 stents per study lesion, with a stent length per patient of about 19 mm.

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