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The mechanism behind coronary stent thrombosis may vary depending on the stent type and whether it occurs early or later on, images from optical coherence tomography (OCT) suggested.

Overall, stent underexpansion (stent expansion index <0.8) was observed in in the PRESTIGE registry, Robert Byrne, MB BCh, PhD, of Germany's Deutsches Herzzentrum München, and colleagues reported in Circulation.

In patients presenting with very late stent thrombosis, uncovered stent struts were especially common in drug-eluting stents, while neoatherosclerosis was especially common in bare metal stents.

In the acute period within 24 hours of implantation and subacute period from 24 hours to 30 days, stent thrombosis was nearly always associated with uncovered or thrombus-covered struts in at least one frame (predicted average probability 99.3% and 96.6%, respectively).

During the late and very late periods (31 days to 1 year and beyond 1 year post-stenting, respectively), uncovered or thrombus-covered struts were less likely to be seen with stent thrombosis (34.3% and 9.6%).

Malapposed struts were less common in the setting of stent thrombosis. OCT images showed these in 21.8%, 8.5%, 6.7%, and 2.0% of patients over the acute, subacute, late, and very late periods.

The dominant common OCT findings with stent thrombosis were:

• In the acute period, uncovered struts (66.7%)
• In the subacute period, uncovered struts (61.7%) and underexpansion (25.5%)
• In late cases, uncovered struts (33.3%) and severe restenosis (19.1%)
• For very late stent thrombosis, neoatherosclerosis (31.3%) and uncovered struts (20.2%)

"When categorizing patients according to timing of stent thrombosis, some clear messages emerge. In patients presenting with acute/subacute stent thrombosis, uncovered and malapposed stent struts along with underexpansion of the stented coronary segment were identified as key morphological features of stent thrombosis by OCT," Byrne's group concluded.

"While it is not unexpected that uncovered stent struts were frequently observed early after stent implantation, this emphasizes the inherent thrombogenicity of stents in this phase, when neointimal healing and re-endothelialization are incomplete. Similarly, although the relevance of stent malapposition in isolation is somewhat unclear, the finding of high rates of malapposition in our report is in line with other reports."

"In patients presenting with late/very late stent thrombosis, a more heterogeneous profile was observed, with uncovered/malapposed stent struts, underexpansion and severe restenosis predominant features within the first year and in-stent neoatherosclerosis beyond 1-year."

How operators can prevent neoatherosclerosis is an important unmet need for future clinical investigation, the investigators said.

The prospective, multicenter PRESTIGE registry had 675 patients enrolled from European centers. In the end, the 231 consecutive patients who got OCT imaging were included in Byrne's analysis (6.1% had poor imaging that precluded further analysis). Stent thrombosis was mostly reported during the late or very late periods (71.4% of cases).

Half of patients received new-generation drug-eluting stents; fewer got bare metal stents (33.0%), and first-generation drug-eluting stents (13.9%).

Among the study's limitations were the lack of a control group without stent thrombosis and the possibility that mechanisms other than those detectable by OCT predominate.

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