Background--Matrix metalloproteinase-9 could exhibit an important role in the destabilization of atherosclerotic carotid plaques. We hypothesized that in patients with carotid stenosis, elevated levels of plasma matrix metalloproteinase-9 are associated with ipsilateral stroke or cardiovascular death.

Methods and Results--We followed up 207 patients with 50% carotid stenosis initially for a mean of 4.4 years, during which time 53 patients developed ipsilateral stroke or died of cardiovascular causes. The cumulative incidence of ipsilateral stroke or cardiovascular death was higher in those with matrix metalloproteinase-9 above versus below the median of 41.9 ng/mL (log-rank P=0.002). Matrix metalloproteinase-9 above versus below the median had a hazard ratio for ipsilateral stroke or cardiovascular death of 1.9 (95% confidence interval [CI], 1.1 to 3.5); during extended follow-up, this remained significant until 10 years. The absolute risk of ipsilateral stroke or cardiovascular death at 4.4 years was 34% and 17% in those with matrix metalloproteinase-9 above and below the median, respectively. Elevated matrix metalloproteinase-9 and an echolucent plaque on B-mode ultrasound versus a low matrix metalloproteinase-9 and an echorich plaque had a hazard ratio for ipsilateral stroke or cardiovascular death of 4.4 (95% CI, 1.8 to 11.1) and for ipsilateral stroke of 3.3 (95% CI, 1.1 to 9.7).

Conclusions--Elevated levels of matrix metalloproteinase-9 in patients with 50% carotid stenosis were associated with a 2-fold risk of ipsilateral stroke or cardiovascular death. Combining elevated matrix metalloproteinase-9 and plaque echolucency was associated with a 4-fold risk for ipsilateral stroke or cardiovascular death and a 3-fold risk for ipsilateral stroke.