For decades, percutaneous coronary intervention (PCI) has largely been guided solely by angiography, despite its well-documented limitations.1 Angiography offers a two-dimensional view of a three-dimensional structure and does very little to delineate the composition of the coronary artery. Additionally, angiography poorly quantitates the severity and location of calcium, does not provide information about plaque morphology, nor does it provide highly accurate and reproducible lumen sizing. For PCI, the operator is limited by angiography in identifying stent malapposition or under-expansion, edge dissections, or plaque protrusion. In short, we have not been seeing the full story. By providing the highest resolution (10-20 μm) images, optical coherence tomography (OCT) now promises to change the nature of how patients are treated.
A New Approach to PCI
OCT is an intracoronary imaging platform that uses light-based technology to help measure coronary arteries from inside the vessel with high precision, allowing for assessment of the degree and characteristics of coronary artery disease. With automated, highly accurate measurements, the technology can guide stent selection, placement, and deployment.
OCT can be used prior to stent implantation in order to accurately measure dimensions and select a stent that best fits the vessel. OCT also helps ensure that the stent is fully expanded and flush against a vessel wall, factors that are critical in reducing stent failure.2 Additionally, OCT is an invaluable tool to assess previously deployed stents in follow-up angiography.
With angiography alone, the operator is left with more subjective assessments of the coronary artery. Visualizing the vessel in 3D with the highest resolution images can quantify lesion severity more accurately, and provides for optimal assessment of lesion morphology in “hazy” angiography situations.
Intracoronary calcium is the Achilles’ heel of successful PCI, making stent delivery difficult, leading to suboptimal stent expansion, and increasing procedural time and complications. Angiography severely underestimates the severity of intracoronary calcium. Therefore, the reliance on angiography alone to guide PCI in severely calcified vessels is associated with poor outcomes.3 OCT is an ideal modality to quantitate the angle and thickness of severe calcium, thus crucial in assessing the need for atherectomy-assisted PCI.
OCT imaging continues to provide crucial details that alter PCI management. In ILUMIEN I4, pre-PCI OCT altered PCI strategy in over half of the cases. Equally, post-PCI OCT has a significant impact on management, predominantly identifying stent under-expansion, malapposition, plaque protrusion, and edge dissections. OCT resulted in larger balloon size, more frequent post-dilatation, larger maximum balloon size and higher balloon pressure than did angiography guidance alone. In CLI-OPCI5, an OCT-guided PCI strategy was associated with improved clinical outcomes specifically with reduction in cardiac death or MI. Future randomized trials will focus on answering the question of whether OCT-guided PCI is superior to angiography alone.
Last year, Abbott began a large-scale randomized trial to evaluate the superiority of OCT versus angiography in patients with complex or high-risk coronary artery disease who receive a stent. The trial, called ILUMIEN IV, is a prospective, single-blind, multi-center randomized study that will evaluate OCT-guided versus angiography-guided coronary stent procedures in complex and high-risk patients and involves almost 4,000 patients at 125 centers in North America, Europe and Asia. Previous ILUMIEN trials have shown that stent procedures using this imaging technology resulted in superior stent expansion and greater procedural success.2
Identifying and Addressing Challenges With New Technology
OCT technology requires the use of a contrast flush to displace blood and provide a clear path for the detection of the light beams. In order to reduce the risk of contrast-induced nephropathy in patients with renal disease, limiting the amount of contrast exposure is crucial. Although OCT cases have demonstrated slightly higher contrast loads, its use has not been associated with acute kidney injury.6 Pre-procedure hydration, limiting nephrotoxic medications, selecting low-osmolar contrast agents, and working closely with nephrologists are key strategies to help reduce renal injury. Additional techniques to reduce contrast load, such as bi-plane angiography, limiting angiograms to OCT runs, and staging elective PCIs, are recommended. Given OCT imaging’s potential for improving PCI outcomes and the techniques for lowering the risks to patients, renal disease should rarely limit the use of OCT imaging.
Another challenge to OCT technology is its limited use in aorto-ostial segments as well as in large diameter vessels. The inability to adequately displace blood given the aortic pressure limits OCT use in this setting. Additionally, the limited far-field range of OCT minimizes its utility in interrogating large vessels, aneurysmal arteries, or vein grafts. These scenarios clearly demonstrate the need for proceduralists to understand OCT and IVUS are not mutually exclusive but rather complementary technologies. OCT is not designed to displace IVUS, particularly in the cases where OCT is limited. Physicians and their staff should be competent and comfortable using both modalities.
While special training in the use of OCT is not mandatory, it is recommended, and national courses are available for interventionalists to observe procedures and practice using the technology. The use of OCT is dramatically increasing to the point that the imaging technology has been part of the Interventional Cardiology Board Exam for several years. The use of OCT is common in Europe and Japan; Dutch, German and Italian registries have also produced robust data and research supporting its use and broad applications over the last decade.
The Bottom Line: A Positive Impact on Patients
How will the adoption of OCT impact the success of a cath lab? With OCT comes innovative and potentially life-saving technology that helps optimize procedural decision making, with the ultimate goal being better patient outcomes.
Disclosure: Dr. Reyes reports he is a consultant to Abbott Vascular.
Dr. Manuel M. Reyes can be contacted at 6400 Fannin Street, Suite 3000, Houston, TX 77030.
- Ali ZA, Maehara A, Genereux P, et al. Optical coherence tomography compared with intravascular ultrasound and with angiography to guide coronary stent implantation (ILUMIEN III: OPTIMIZE PCI): a randomized controlled trial. Lancet. 2016 November; (388) 2618.
- Ali ZA, Maehara A, Généreux P, et al; ILUMIEN III: OPTIMIZE PCI Investigators. Optical coherence tomography compared with intravascular ultrasound and with angiography to guide coronary stent implantation (ILUMIEN III: OPTIMIZE PCI): a randomised controlled trial. Lancet. 2016 Nov 26; 388(10060): 2618-2628. doi: 10.1016/S0140-6736(16)31922-5.
- Mehanna E, Abbott JD, Bezerra HG, et al. Optimizing percutaneous coronary intervention in calcified lesions: Insights from optical coherence tomography of atherectomy. Circulation: Cardiovascular Interventions. May 2018; (11) 1.
- Wijns W, Shite J, Jones MR, et al. Optical coherence tomography imaging during percutaneous coronary intervention impacts physician decision-making: ILUMIEN I study. European Heart Journal. 2015 December; (36) 3354.
- Prati F, Di Vito L, Biondi-Zoccai G, et al. Angiography alone versus angiography plus optical coherence tomography to guide decision-making during percutaneous coronary intervention: the Centro per la Lotta contro l’Infarto-Optimisation of Percutaneous Coronary Intervention (CLI-OPCI) study. EuroIntervention. 2012; 8: 823-829. doi: 10.4244/EIJV8I7A125.
- Meneveau N, Souteyrand G, Motreff P, et al. Optical coherence tomography to optimize results of percutaneous coronary intervention in patients with non-ST-elevation acute coronary syndrome: results of the multicenter, randomized DOCTORS study (Does Optical Coherence Tomography Optimize Results of Stenting). Circulation. 2016 Sep 27; 134(13): 906-917. doi: 10.1161/CIRCULATIONAHA.116.024393.