Optical Coherence Tomography-Guided Percutaneous Coronary Interventions

Optical coherence tomography (OCT) has emerged as a technological breakthrough in the field of intracoronary imaging by providing high-resolution in vivo images with near histological detail. Coronary OCT consists of a fiberoptic wire that emits light in the near infrared spectrum (1,250–1,350 nm), records reflected light signals while rotating and being simultaneously pulled back along the long axis of a coronary vessel.¹ Though the application of OCT during percutaneous coronary interventions (PCI) seems logical and promising, its widespread adoption will only be possible after a thorough evaluation of its capabilities and limitations in comparison to the more traditional intravascular ultrasound (IVUS) imaging. In this issue of the journal, Kawamori et al provide an interesting and informative insight into comparative advantages of OCT and IVUS guided PCI.² Prior to diving into the details of each of these techniques with respect to their ability to detect vessel size, stent expansion, dissection, plaque prolapse and intracoronary thrombus, it is important to highlight that the OCT system used for this study was ‘time-domain’ OCT or TD-OCT with a mechanically-scanned reference arm. Moreover, TD-OCT requires the inflation of a proximally placed balloon that may limit its ability to image unprotected left main coronary artery, ostial and proximal lesions and heavily calcified or diffusely diseased coronary segments.3 The newer generation of intravascular OCT uses a fixed mirror with variable light frequency and is termed frequency or Fourier-domain OCT (FD-OCT). This allows faster imaging by simultaneous detection of all echo time delays and without the need for proximal balloon inflation. A blood-free imaging environment is created by the combination of fast pullback speed and high-rate (4 cc/sec) saline infusion.³ It is customary to find a FD-OCT system at most U.S. sites. Though, longer light wavelengths can provide greater tissue penetration, current intravascular OCT use of 1,300 nm light source provides 1–3 mm tissue penetration compared to 4–8 mm IVUS penetration, with the exception of calcified lesions. Axial resolution of OCT is 12–18 µm, compared to 150–200 µm for IVUS and lateral resolution of OCT is 20–90 µm and that of IVUS is 150–300 µm.⁴ The investigators provide key pre-PCI and post-PCI quantitative and qualitative assessment of the coronary vessels undergoing a coronary stent implant. An important observation made by the investigating team includes the detection of significantly smaller lumen parameters distal to a ≥ 75% stenosed coronary lesion while near identical pre-lesion vessel dimensions obtained by TD-OCT and IVUS. This observation may have great relevance during OCT-guided stent size selection. The authors also offer potential explanations for this observation associated to a distal low flow state secondary to the proximal balloon inflation required for TD-OCT intravascular imaging. It is intuitive that FD-OCT will be devoid of this important limitation. The claim by the investigators that intravascular OCT provides more detailed information of the presence of tissue prolapse, thrombus formation and edge dissection than IVUS during PCI is supported by prior observations.⁵ However, the pathway to the use of this information for guiding treatment strategies is not addressed in this manuscript. Given the scope of this report, additional studies to record clinical utility of these findings are needed. Detection of a significantly greater number of stent malappositions, edge dissections and thombus overlays certainly drive home the point that less sensitive, low-resolution IVUS imaging has the potential to underestimate mechanical problems following a coronary stent implant which may have important clinical implications. However, this needs to be tested in large-scale clinical outcome trials. Other investigators, who have made similar comparative evaluations of intravascular OCT and IVUS imaging techniques have reported no correlation between the significantly greater number of stent malappositions, edge dissections or thrombus to early or late clinical events.⁶ The authors provide a well-balanced comparison of the two contemporary in vivo coronary imaging techniques used during PCI and acknowledge important limitations of their study. They however provide no assessment of the ability of intravascular OCT- and IVUS-derived characterization of the vessel wall, plaque characteristics and intermediate coronary lesion assessment, which are common indications for the use of intracoronary imaging modalities. The issue of imaging artifacts also remains unaddressed. These factors have an important role in comparative assessment of intravascular OCT and IVUS during PCI.⁷ We believe that this report is a valuable addition to the growing evidence on intravascular OCT and will be well received by the interventional community.

References

1. Bezerra HG, Costa MA, Guagliumi G, et al. Intracoronary optical coherence tomography: A comprehensive review. JACC Cardiovasc Interv 2009;2:1035–1046. 2. Kawamori H, Shite J, Shinke T, Otake H. The ability of optical coherence tomography to monitor percutaneous coronary intervention: Detailed comparison with intravascular ultrasound. J Invasive Cardiol 2010;22:541–545. 3. Chinn SR, Swanson EA, Fujimoto JG. Optical coherence tomography using a frequency-tunable optical source. Opt Lett 1997;22:340–342. 4. Liu B, Brezinski ME. Theoretical and practical considerations on detection performance of time domain, Fourier domain, and swept source optical coherence tomography. J Biomed Opt 2007;12:044007. 5. Gonzalo N, Barlis P, Serruys PW, et al. Incomplete stent apposition and delayed tissue coverage are more frequent in drug-eluting stents implanted during primary percutaneous coronary intervention for ST-segment elevation myocardial infarction than in drug-eluting stents implanted for stable/unstable angina: Insights from optical coherence tomography. JACC Cardiovasc Interv 2009;2:445–452. 6. Gonzalo N, Serruys PW, Okamura T, et al. Optical coherence tomography assessment of the acute effects of stent implantation on the vessel wall: A systematic quantitative approach. Heart 2009;95:1913–1919. 7. Di Mario C, Barlis P. Optical coherence tomography: A new tool to detect tissue coverage in drug-eluting stents. JACC Cardiovasc Interv 2008;1:174–175.

———————————————————— From the University of Texas Southwestern Medical Center, Dallas, Texas and VA North Texas Health Care System, Dallas, Texas. Disclosures: Dr. Banerjee reports receiving speaker honoraria from St. Jude Medical, Medtronic, Gilead and Johnson & Johnson; research support from Boston Scientific and The Medicines Company. Dr Iqbal reports no conflicts of interest, Dr. Brilakis reports speaker honoraria from St. Jude Medical; consulting fees from Medicure; research support from Abbott Vascular; and salary from Medtronic (spouse). Address for correspondence: Subhash Banerjee, MD, 4500 S Lancaster Road (111a), Dallas, TX 75216. E-mail: subhash.banerjee@utsouthwestern.edu