Читать книгу Interventional Cardiology - Группа авторов - Страница 240

The widespread application of a non‐occlusive technique using monorail OCT catheters, the high pullback speed allowed by newer generation FD‐OCT systems, the introduction of coregistration techniques and the availability of semi‐automatic measurements have made OCT a potential alternative for guidance of percutaneous coronary interventions (PCI), overcoming drawbacks of coronary angiography and avoiding the difficulties in interpretation and quantification of IVUS (Figure 9.4). However, it is very important to understand that OCT and IVUS are not interchangeable techniques; they have advantages, limitations, and differences in the way the procedure is guided via online measurements during the PCI procedure.

Figure 9.4 Optical coherence tomography in coronary interventions. (a) Strut malapposition. Malapposed struts can be seen between 12 and 6 o’clock. (b) Intracoronary thrombus formation during coronary intervention. (c) Edge dissection. (d) Tissue prolapse. (e) Neointimal coverage of stent struts in the follow‐up. (f) Intimal coverage of malapposed struts (arrow). (g) Neointimal hyperplasia. (h) In‐stent restenosis. (i) Bioabsorbable vascular scaffold (BVS). Note BVS struts are transparent to light. (j) BVS in the follow‐up.

Because of the sharp delineation of lumen contours, OCT easily provides automatic lumen measurements (Figure 9.5). Accurate measurement of the reference lumen dimensions allows for optimal stent diameter selection, while the precise identification of the longitudinal extent of the atherosclerotic plaque facilitates selection of the most appropriate stent length and landing zones. The visualization of stent expansion permits optimization with high pressure post‐dilatation, in the case of focal underexpansion readily demonstrated in the online lumen profile maps of modern OCT systems. In a recent study, which compared FD‐OCT, IVUS, and quantitative coronary angiography [51], the mean minimum lumen diameter measured by quantitive coronary angiography (QCA) was smaller than by OCT, which was smaller than that by IVUS, a result consistent with a previous report [52]. Using a phantom model, investigators showed that mean lumen area (MLA) according to FD‐OCT was equal to the actual lumen area of the phantom model while IVUS overestimated the lumen area and was less reproducible than FD‐OCT. In addition to cross‐sectional measurements, FD‐OCT also provides accurate longitudinal measurements [53]. The main difference with IVUS, however, is the inability of OCT to measure the media‐to‐media diameter in most cases, with the rare exception of some distal reference segments with very small plaque burden and vessel diameter.

Figure 9.5a Baseline angiogram of the the right coronary system shown on the left with a red arrow at the site of maximal stenosis in the mid‐RCA. The other two panels show the baseline OCT interface with the co‐registered angiogram in the upper left corner, OCT cross‐section upper right corner, and longitudinal profile and “L‐mode” at the lower portion of the image. Panel A highlights the measurements at the distal reference, with an EEL diameter of 3.23mm. Panel B demonstrates the measurements at the proximal reference with an EEL diameter of 3.65mm. These measurements are obtained manually. The distance between distal and proximal reference is automatically calculated and determines the stent length. In this example, the length is 18mm and circled in red. The minimum lumen area (MLA) is automatically localized and measured, and in this case is 1.13mm².

Figure 9.5b OCT following stent implantation with stent rendering on the longitudinal profile. The color‐coded apposition bar confirms complete stent apposition. Stent expansion is automatically detected and demonstrates 73% in the distal portion of the stent and 90% for the proximal portion of the stent. The minimum stent area (MSA) is automatically localized and measured.

Figure 9.5c Final angiogram of the RCA following PCI is shown in the left image. Following stent optimization, OCT demonstrates 100% expansion in the distal portion of the stent with 107% expansion in the proximal portion of the stent. The OCT cross‐section confirms no edge dissection.

Several registries have investigated the role of OCT guidance in PCI. After full lesion predilatation, OCT pullback imaging suggested proceeding directly with stenting in 48% while in 52% advised further treatment. Out of the 207 pullback imagings after stenting, 14% suggested new stent implantation because of dissection or residual edge stenosis and 31% suggested further optimization with high pressure or larger sized balloon. A multicenter trial compared the outcomes of an angiographic‐guided strategy with an OCT‐guided strategy in 670 patients [54]. OCT disclosed adverse features requiring further interventions in 35% of cases. OCT guidance was associated with a significantly lower risk of cardiac death or myocardial infarction at one year, even after adjustment for potential confounders.

A more recent trial by Burzotta et al. was aimed to compare OCT guidance and fractional flow reserve guidance in patients with angiographically intermediate coronary lesions in a single‐center, prospective, 1:1 randomized trial; a total of 350 patients were enrolled (176 randomized to FFR and 174 to OCT imaging). The primary endpoint of major adverse cardiac events or significant angina at 13 months occurred in 14.8% of patients in the FFR arm and in 8.0% in the OCT imaging arm (p= 0.048). As stated by the authors, OCT guidance was associated with lower occurrence of the composite of major adverse cardiac events or significant angina [55].

Traditional stent sizing with IVUS is based on measuring lumen, external elastic membrane (EEM) areas or a combination of the two. EEM‐based algorithms result in the selection of larger diameter balloons and stents. With OCT the EEM is more difficult to visualize if a large plaque area is present. Two randomized trials investigated OCT‐guided PCI versus IVUS‐guided PCI: ILUMIEN III examined 450 patients and showed that OCT‐guided PCI was non‐inferior to IVUS‐guided PCI. In this trial in 85% of cases the EEM‐area could be delineated in the distal reference leading to an aggressive strategy partially based on EEM‐area. In this trial OCT‐detected major stent edge dissections (dissection flap >60 degrees or >3 mm in length) were less common in the OCT‐guided arm versus the IVUS‐guided arm, and, when present, they were observed less frequently by IVUS than by OCT [59–67]. OCT guidance resulted in more frequent postdilatation, larger maximum balloon size, and higher balloon pressure than did angiography guidance alone. Intraprocedural MACEs were uncommon occurring similarly in the three groups, OCT, IVUS, and angiography alone. The Japanese OPINION trial included 829 patients and tested whether OCT‐guided PCI using a lumen‐based approach was non‐inferior to IVUS‐guided PCI with the primary endpoint of target vessel failure within 12 months, defined as a composite of cardiac death, target‐vessel related myocardial infarction and ischaemia‐driven target lesion revascularization). Primary endpoint did not differ, and also in‐stent minimum lumen diameter and binary restenosis, assessed with repeated angiography, were similar. A recent metanalysis by Buccheri et al. of 17 882 patients demonstrated an important MACE reduction and cardiovascular mortality using OCT‐ and/or IVUS‐guided versus angiography‐guided PCI alone [56, 57, 58]. The impact of OCT‐guided vs angiography‐guided PCI is being investigated with the same difference in endpoint selection by two larger OCT guided stenting protocols: ILUMIEN‐IV (NCT0350777) and OCTOBER trials (NCT03171311), both ongoing, see clinicaltrials.com.

IVUS post‐PCI MSA is the strongest predictor of both restenosis and thrombosis. OCT‐MSA was also found to be an independent predictor of device‐oriented clinical endpoints and target lesion revascularisation, with an MSA cutoff value of 5.0 mm² for DES and 5.6 mm² for bare metal stents. OCT MSA <5.0 mm² was found in about one‐third of patients in ILUMIEN III trial, confirming that a small stent area is common in clinical practice.