OCT is a brand-new intravascular imaging method that uses light and produces high-resolution cross-sectional pictures of coronary artery architecture. Similar to intravascular ultrasonography (IVUS), OCT image capture makes use of near-infrared light rather than ultrasound. OCT's use of light results in about a 10-fold increase in resolution over IVUS (10–15 vs. 100–150 m), enhancing its capacity to describe plaque, image artery wall anatomy, and aid in both short- and long-term follow-up of coronary procedures.
Recent developments in OCT technology have made it possible to get images more quickly, eliminating the requirement for proximal balloon occlusion and making the procedure simpler and safer. Many people think OCT will take the place of IVUS as the industry standard for intravascular imaging because of how simple it is to acquire. However, because of its shallower depth of penetration (1.5 mm as opposed to 5) and inability to image ostial disease, OCT continues to be inferior to IVUS in assessing plaque burden and vascular remodeling (eg, unable to clear blood in the ostium). This article focuses on the various applications of OCT and discusses its benefits and drawbacks in comparison to IVUS.
The intravascular imaging techniques optical coherence tomography (OCT) and intravascular ultrasonography (IVUS) are frequently employed in the cardiac catheterization lab. A variety of clinical evidence supports the effectiveness of these modalities for enhancing the immediate and long-term clinical impact following percutaneous coronary intervention (PCI). For improved lesion preparation, ideal stent sizing, identifying post-PCI problems, and determining the cause of stent failure, intravascular imaging offers unique information. The main characteristics of these imaging modalities used during PCI are compared and contrasted in this review.
Clinical results are considerably enhanced by intravascular imaging guidance during the percutaneous coronary intervention (PCI). The two intravascular imaging technologies that are commercially accessible that are used to direct choices and enhance PCIs are intravascular ultrasound (IVUS) and optical coherence tomography (OCT). By providing adequate information to clinicians regarding true vessel size, landing zones to guide stent length selection, plaque morphology to guide debulking strategies, and PCI complications (edge dissection, stent malapposition), as well as stent failure mechanisms (stent thrombosis/under expansion/fracture, neointimal hyperplasia, no atherosclerosis), intravascular imaging guidance improve outcomes. In this review, the usefulness of IVUS and OCT in modern PCI is compared and contrasted, along with the suitable circumstances in which to apply these opposing imaging modalities.
OCT uses infrared light, whereas IVUS uses ultrasound. OCT provides ten times more resolution than IVUS, although it still necessitates blood clearance, usually with contrast but also with dextran as a contrast-sparing agent. Compared to IVUS, OCT has a lower penetration (1-2 mm) (5–6 mm). The presence of a red thrombus degrades the OCT image quality. The short wavelength of red blood cells causes "structural noise," which distorts the image. Compared to IVUS, OCT pictures ar Contrarily, IVUS offers view of all three artery layers, and its depth of penetration allows one to evaluate vascular remodeling, which in turn more effectively directs ideal vessel sizing and facilitates the implantation of larger-sized stents. Compared to IVUS, OCT has a lower depth but a higher resolution. With high definition-IVUS, the resolution has increased and genuine vessel size can now be better evaluated than with OCT for the best stent choice more repeatable due to their higher resolution.
Coronary calcification is only detected by angiography in as little as 40% of cases, but when it is, the calcific burden is higher. IVUS has a sensitivity of almost 90% and a specificity range of 97-100% when compared to anatomical pathology for detecting plaque calcification. Given that calcium reflects ultrasonic waves, OCT enables a more accurate visualization and image penetration in calcific coronary disease than IVUS. As a result, OCT provides more precise information about calcium depth and regionality. In the absence of proper plaque modification prior to stenting, PCI in patients with significant calcific coronary disease is difficult and hinders stent expansion. A calcification arc of >180° and depth >0.5 mm thick are predictive of worse outcomes as a result of stent under-expansion and this finding on intravascular imaging should prompt the operator to consider adjunctive plaque modification strategies (like cutting/scoring balloons and/or rotational atherectomy).
OCT-guided rotational atherectomy and IVUS-guided rotational atherectomy were contrasted in a 247-patient Japanese study. The results showed that the OCT-guided rotational atherectomy group employed a final burr size that was considerably bigger (1.75 vs. 1.50 mm, P=0.001) and a higher percentage of stent expansion (83% vs. 72%, P=0.0004) than the IVUS-guided cohort. Target lesion revascularization (TLR) rates, however, were comparable in the 2 cohorts. To achieve proper stent expansion in calcified coronary lesions, atherectomy (laser/cutting or scoring balloon/rotational/orbital atherectomy) is an essential component of intravascular imaging.
On the basis of OCT, circumferential calcific illness or the presence of calcific arcs >270° arc can be efficiently treated using coronary intravascular lithotripsy balloons. OCT, IVUS, and quantitative coronary angiography are being compared in a three-arm experiment (NCT03574636) for moderate-severely calcified lesions during PCI. In-stent late lumen loss is the trial's main goal (difference between the minimal lumen diameter immediately post PCI and the minimal lumen diameter by angiography review at 13 months’ post PCI).
Prior to stent placement, it has been shown that intravascular imaging utilizing OCT or IVUS can predict slow flow or no-reflow phenomena and the ensuing peri-procedural myocardial infarction. The attenuated plaque suggestive of a large necrotic core on IVUS, acute plaque rupture, or thin fibrous cap atheroma was the plaque features predictive of these unfavorable outcomes. It was found that the capacity to forecast the no-reflow phenomena was connected with an attenuated plaque on IVUS that had a longitudinal length of more than 5 mm. Echo signal attenuated plaque was independently linked with the no-reflow phenomenon with an odds ratio of 5.59 (95% CI: 2.64-11.85) in an investigation of 336 people with acute coronary syndromes (ACS). In an effort to reduce no-reflow and periprocedural myocardial infarction, further measures like intracoronary enalaprilat or a distal filter protection device could be taken if these higher-risk traits are discovered on intravascular pre-PCI imaging.
The first significant trial to offer standards for bare-metal stent optimization was the Multicenter Ultrasound Stenting in Coronaries Study (MUSIC). This included a minimum stent area (MSA) 80% of the average reference lumen area or 90% of the smaller reference lumen, or an MSA >9 mm2 with a minimum MSA of 90% of the average reference lumen area or 100% of the smaller reference lumen. At six months, the incidence of TLR was lower when these conditions were met. The distal vessel segment's external elastic membrane (EEM) diameter, less than 0.5 mm, is used to determine the appropriate stent size in the drug-eluting stent era. The proximal reference vessel diameter is occasionally used as the reference balloon size to post-dilate the stent. The Multicenter Coronary Ultrasound Stenting According to the AVIO trial, the ideal MSA should be based on an IVUS-guided balloon area at nominal pressure.
Poor outcomes, including stent failure, are independently predicted by a reduced post-PCI MSA (or stent under-expansion) (thrombosis and restenosis). The ideal MSA cutoff on IVUS for the majority of drug-eluting stents lies between 5.3 and 5.7 mm2 in the non-left main segments. Similar to this, the MSA threshold value of 5.0 mm2 for drug-eluting stents was an independent predictor of significant adverse cardiac events and TLR based on a large OCT registry of 786 patients. Another examination of 832 patients showed that significant adverse cardiac events were independently linked with MSA values of 4.5 mm2 on OCT.
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