A novel quantitative method for evaluating diffuse in-stent narrowing at follow-up angiography

A new quantitative parameter, diffuse index (DI), was proposed to evaluate objectively whether in‐stent restenosis is diffuse or focal in nature. A total of 343 patients (346 lesions) with Wiktor‐GX, AVE MS‐II, or JOMED stents were evaluated at follow‐up angiography. According to the QCA‐CMS definition, lesion length is derived from the 100% reference diameter function (RDF). By moving the RDF downward, the lesion length, LL(x), at each percentage x of the RDF can be calculated. We have defined the DI by the ratio of this calculated length LL(x) and the total stent length, SL, in other words, DI = [LL(x)/SL]. The percentage plaque area (% PA) was calculated by dividing the plaque area by the sum of the plaque area and luminal area within the stent. An excellent correlation was found between the DI at 88% RDF and the % PA in all three stents (r > 0.88). The individual correlation curves were nearly identical, independent of the type of stent. Furthermore, based on the overall data, the combination of a DI > 0.8 and % PA > 30% correlated with a high incidence of subsequent major adverse cardiac events (13/25 = 52%). From these data, it can be concluded that the diffuse index is a new objective quantitative parameter to describe whether in‐stent restenosis is of focal or diffuse nature. Cathet Cardiovasc Intervent 2001;54:309–317. © 2001 Wiley‐Liss, Inc.